Molecular findings in patients for whole exome sequencing and mitochondrial genome assessment.

OBJECTIVE: Whole exome sequencing (WES) is becoming more widely used as a diagnostic tool in the field of medicine. In this article, we reported the diagnostic yield of WES and mitochondrial genome assessment in 2226 consecutive cases in a single clinical laboratory. MATERIALS AND METHODS: We retrospectively analyzed consecutive WES reports from 2226 patients with various genetic disorders. WES-process was focused exclusively on the probands and aimed at a higher diagnostic capacity. We determined the diagnostic rate of WES overall and by phenotypic category, mode of inheritance, mitochondrial genome variant, and copy number variants (CNVs). RESULTS: Among the 2226 patients who had diagnostic WES proband-only, the overall diagnostic yield of WES was 34.59% (770/2226). The highest diagnostic yield was observed in autosomal dominant disorders, at 45.58% (351/770), followed by autosomal recessive at 31.95%(246/770), X-linked disorder at 9.61%(74/770), and mitochondrial diseases at a notably lower 0.65%(5/770). The 12.21% (94/770) diagnoses were based on a total of 94 copy number variants reported from WES data. CNVs in children accounted for 67.02% of the total CNVs. While majority of the molecular diagnoses were related to nuclear genes, the inclusion of mitochondrial genome sequencing in the WES test contributed to five diagnoses. all mitochondrial diseases were identified in adults. CONCLUSIONS: The proband-only WES provided a definitive molecular diagnosis for 34.59% of a large cohort of patients while analysis of WES simultaneously analyzed the SNVs, exons, mitochondrial genome, and CNVs, thereby improving the diagnostic yield significantly compared to the single-detection WES method; and facilitating the identification of novel candidate genes.

Prenatal exome sequencing for morphologically normal fetus: Should we be doing it?

OBJECTIVE: We aimed to investigate the yield of prenatal exome sequencing (pES) in morphologically normal fetuses. METHOD: This retrospective study analyzed 254 families with morphologically normal fetuses who underwent prenatal trio exome sequencing based on parental request between September 2020 and October 2023. RESULTS: Overall, abnormal findings were detected in 8 families (3.1%, 8/254) by pES. Among these, 6 families (2.3%, 6/254) were found to have fetuses affected with monogenic disorders (2 autosomal recessive conditions and 4 autosomal dominant conditions), while 2 families (0.8%, 2/254) were incidentally found to be couples at risk of having a future pregnancy with a recessive condition. Among the six fetuses detected with monogenic disorders, two fetuses carried a de novo variant in OPA1 and NF1, which are known to cause Optic atrophy 1 and Neurofibromatosis, respectively. One fetus was detected with a maternally inherited variant in PKD2 related to polycystic kidney disease 2 (not known to the mother until then). One fetus was detected with a maternally inherited variant in SDHB associated with Pheochromocytoma. Two fetuses carried compound heterozygous variants in NAGLU and GJB2 associated with Mucopolysaccharidosis type IIIB and Deafness, respectively. In the 2 families where parents were found to be carriers but the fetuses were unaffected, heterozygous variants in the GJB2 and SERPINB7 genes were detected in the parents, respectively, which are associated with deafness and palmoplantar keratoderma. CONCLUSION: Our research indicated that pES can provide significant critical information for families with morphologically normal fetuses. Prenatal screening with exome sequencing requires careful management and detailed pre-test and post-test genetic counseling.

Genetic analysis of 37 cases with primary periodic paralysis in Chinese patients.

BACKGROUND: Primary periodic paralysis (PPP) is an inherited disorders of ion channel dysfunction characterized by recurrent episodes of flaccid muscle weakness, which can classified as hypokalemic (HypoPP), normokalemic (NormoPP), or hyperkalemic (HyperPP) according to the potassium level during the paralytic attacks. However, PPP is charactered by remarkable clinical and genetic heterogeneity, and the diagnosis of suspected patients is based on the characteristic clinical presentation then confirmed by genetic testing. At present, there are only limited cohort studies on PPP in the Chinese population. RESULTS: We included 37 patients with a clinical diagnosis of PPP. Eleven (29.7%) patients were tested using a specific gene panel and 26 (70.3%) by the whole-exome sequencing (WES). Twenty-two cases had a genetic variant identified, representing a diagnostic rate of 59.5% (22/37). All the identified mutations were either in the SCN4A or the CACNA1S gene. The overall detection rate was comparable between the panel (54.5%: 6/11) and WES (61.5%: 16/26). The remaining patients unresolved through panel sequencing were further analyzed by WES, without the detection of any mutation. The novel atypical splicing variant c.2020-5G > A affects the normal splicing of the SCN4A mRNA, which was confirmed by minigene splicing assay. Among 21 patients with HypoPP, 15 patients were classified as HypoPP-2 with SCN4A variants, and 6 HypoPP-1 patients had CACNA1S variants. CONCLUSIONS: Our results suggest that SCN4A alleles are the main cause in our cohort, with the remainder caused by CACNA1S alleles, which are the predominant cause in Europe and the United States. Additionally, this study identified 3 novel SCN4A and 2 novel CACNA1S variants, broadening the mutation spectrum of genes associated with PPP.

[Genetic analysis of a case with Al Kaissi syndrome and a literature review].

OBJECTIVE: To explore the genetic etiology of a child with delayed growth and development and carry out a literature review. METHODS: A child suspected for Al Kaissi syndrome at the First Affiliated Hospital of Zhengzhou University on March 6, 2021 was selected as the study subject. Following extraction of genomic DNA, the child was subjected to copy number variation sequencing (CNV-seq) and whole exome sequencing (WES), and candidate variants were verified by PCR-agarose gel electrophoresis and quantitative real-time PCR (qPCR). Prenatal diagnosis was conducted on chorionic villi sample upon subsequent pregnancy. RESULTS: The child, a 6-year-and-4-month-old boy, has dysmorphic features including low-set protruding ears and triangular face, delayed language and intellectual development, and ventricular septal defect. CNV-seq result has found no obvious abnormality, whilst WES revealed homozygous deletion of exons 1 and 2 of the CDK10 gene, which was confirmed by PCR-agarose gel electrophoresis and qPCR. Both of his parents were heterozygous carriers. Prenatal diagnosis using chorionic villi samples suggested that the fetus also carried the heterozygous deletion. CONCLUSION: The clinical features of Al Kaissi syndrome in this child can probably be attributed to the homozygous deletion of exons 1 and 2 of the CDK10 gene.

The uncertainty of copy number variants: pregnancy decisions and clinical follow-up.

BACKGROUND: Next-generation sequencing for copy number variants is often used as a follow-up investigation of unusual fetal ultrasound results and is capable of detecting copy number variations with a resolution of ∼0.1 Mb. In a prenatal setting, observation and subsequent management of pregnancies with a fetal variant of uncertain significance remains problematic for counseling. OBJECTIVE: This study aimed to follow the decision-making processes in pregnancies with a fetal variant of uncertain significance and prospectively assess copy number variation interpretations and implications under the newer 2020 American College of Medical Genetics and Genomics guidelines. STUDY DESIGN: In a single prenatal unit, prospective chromosome testing using copy number variation sequencing for 8030 fetuses with unexpected noninvasive findings identified 139 pregnancies with a copy number variation classified as a variant of uncertain significance according to the 2015 American College of Medical Genetics and Genomics guidelines current at the time. Parent-of-origin testing was subsequently performed to determine if the copy number variation was inherited or de novo. All couples were offered specialized genetic counseling to assist in pregnancy management decisions. For the continued pregnancies that reached term, newborns were clinically assessed for evidence of any disease at 0 to 10 months and/or at 2 to 4 years of age. RESULTS: Of the 139 variants of uncertain significance found, most (78%) were inherited with no evidence of disease in the carrier parent. On the basis of primary ultrasound findings combined with results from noninvasive prenatal screening tests, most inherited variant of uncertain significance pregnancies were continued, whereas most pregnancies involving de novo variants of uncertain significance were terminated. From clinical follow-up of the 113 live births, only 5 showed any evidence of a phenotype that was not apparently related to the original variant of uncertain significance. Prospective reanalysis of the 139 variants of uncertain significance using recent 2020 American College of Medical Genetics and Genomics guidelines changed the status of 24 variants of uncertain significance, with 15 reclassified as benign and 9 as pathogenic. However, the 5 children born with an inherited variant of uncertain significance reclassified as pathogenic showed no evidence of a disease phenotype on clinical follow-up. CONCLUSION: The severity of fetal ultrasound findings combined with results from parent-of-origin testing were the key drivers in pregnancy management decisions for patients. According to birth outcomes from continued pregnancies, most variants of uncertain significance proved to be apparently benign in nature and potentially of low risk of adverse disease outcome. There was a discordance rate of 17% for variant of uncertain significance scoring between the 2015 and 2020 American College of Medical Genetics and Genomics guidelines for defining a variant of uncertain significance, suggesting that difficulties remain for predicting true pathogenicity. Nonetheless, with increasing knowledge of population copy number variation polymorphisms, and a more complete assessment for alternative genetic causes, patients having prenatal assessments should feel less anxious when a fetal variant of uncertain significance is identified.

Estimate of genetic variants using CNV-Seq for fetuses with oligohydramnios or polyhydramnios.

BACKGROUND: Oligohydramnios or polyhydramnios, is associated with chromosomal aberrations, particularly aneuploidy. However, its correlation with copy number variation (CNV) remains unclear. METHODS: We retrospectively analyzed 428 cases with an abnormal level of amniotic fluid, comprising of 139 cases of single ultrasound findings (SU group) and 289 cases of multiple ultrasound findings (MU group), by CNV sequencing (CNV-Seq) and followed their pregnancy outcomes. RESULTS: The overall detection rate of clinically significant findings was 8%, with 5% in the SU group and 11% in MU group. Besides, 18 microdeletion/microduplication syndromes were detected, with the highest rate of renal cysts and diabetes syndrome (22%, 4/18). Also, the rate of termination of pregnancy in MU group was much higher than that in the SU group (29% vs. 10%, ***p < 0.001), and in the MU-oligohydramnios subgroup, it was the highest (34%), regardless of cases with chromosomal anomaly and lost to follow-up. CONCLUSION: Our results showed that the abnormal level of amniotic fluid, especially combined with other ultrasound abnormalities, is closely related to chromosomal abnormalities and genetic CNVs. CNV-Seq may be useful in investigating pregnancies with an abnormal amniotic fluid level.

[Prenatal diagnosis of partial deletion of NRXN1 gene with combined CNV-seq and qPCR assays].

OBJECTIVE: To summarize the genetic diagnosis, low-depth copy number variation sequencing (CNV-seq) and prenatal finding in 7 fetuses with 2p16.3 deletions only involving the NRXN1 gene. METHODS: The 7 fetuses have all been found to have loss of heterozygosity at 2p16.3 by CNV-seq, which were verified by quantitative real-time PCR (qPCR). Specific regions of NRXN1 gene deletions were identified, and the CNVs were verified in their parents. Outcome of the pregnancies were followed up. RESULTS: Among 16 502 prenatal samples, 7 fetuses were found to harbor a 120 kb ~ 900 kb microdeletion in the 2p16.3 region, which yielded a prevalence of 0.424‰. The deleted region mainly involved 50 200 000-51 880 000 positions of chromosome 2 and involved only the NRXN1 gene. All of the 7 fetal CNVs were confirmed by qPCR, including 2 cases with heterozygous deletion of exons 1 to 6, 1 with heterozygous deletion of exons 1 to 19, 1 with heterozygous deletion of exons 19 to 22, and 3 with heterozygous deletion of introns 6 to 7 of the NRXN1 gene. Verification in the parents had found that one deletion was inherited from the father, 1 was from the mother, 2 cases were de novo in origin, whilst the remaining 3 had refused parental verification. After genetic counseling, one couple had elected induced abortion, 1 case has not been born yet, whilst the other 5 cases were born healthy. Follow up had identified no mental abnormalities among the children. CONCLUSION: Seven fetuses with heterozygous 2p16.3 deletions only involving the NRXN1 gene were detected by CNV-seq. The specific deletion of the NRXN1 gene was verified by qPCR. Prenatal genetic counseling and fertility guidance has been provided to the particular family by combining the results of CNV testing, pedigree analysis and pregnancy outcome.

A dPCR-NIPT assay for detections of trisomies 21, 18 and 13 in a single-tube reaction-could it replace serum biochemical tests as a primary maternal plasma screening tool?

BACKGROUND: The next generation sequencing (NGS) based non-invasive prenatal test (NIPT) has outplayed the traditional serum biochemical tests (SBT) in screen of fetal aneuploidies with a high sensitivity and specificity. However, it has not been widely used as a primary screen tool due to its high cost and the cheaper SBT is still the choice for primary screen even with well-known shortages in sensitivity and specificity. Here, we report a multiplex droplet digital PCR NIPT (dPCR-NIPT) assay that can detect trisomies 21, 18 and 13 (T21, T18 and T13) in a single tube reaction with a better sensitivity and specificity than the SBT and a much cheaper price than the NGS-NIPT. METHODS: In this study, the dPCR-NIPT assay's non-clinical characteristics were evaluated to verify the cell free fetal DNA (cffDNA) fraction enrichment efficiencies, the target cell free DNA (cfDNA) concentration enrichment, the analytical sensitivity, and the sample quality control on the minimum concentration of cfDNA required for the assay. We validated the clinical performance for this assay by blindly testing 283 clinical maternal plasma samples, including 36 trisomic positive samples, from high risk pregnancies to access its sensitivity and specificity. The cost effectiveness of using the dPCR-NIPT assay as the primary screen tool was also analyzed and compared to that of the existing contingent strategy (CS) using the SBT as the primary screen tool and the strategy of NGS-NIPT as the first-tier screen tool in a simulating situation. RESULTS: For the non-clinical characteristics, the sample processing reagents could enrich the cffDNA fraction by around 2 folds, and the analytical sensitivity showed that the assay was able to detect trisomies at a cffDNA fraction as low as 5% and the extracted cfDNA concentration as low as 0.2 ng/µL. By testing the 283 clinical samples, the dPCR-NIPT assay demonstrated a detection sensitivity of 100% and a specificity of 95.12%. Compared to the existing CS and the NGS-NIPT as the first-tier screen strategy, dPCR-NIPT assay used as a primary screen tool followed by the NGS-NIPT rescreen is the most economical approach to screen pregnant women for fetal aneuploidies without sacrificing the positive detection rate. CONCLUSION: This is the first report on a dPCR-NIPT assay, consisting of all the necessary reagents from sample processing to multiplex dPCR amplification, can detect T21, T18 and T13 in a single tube reaction. The study results reveal that this assay has a sensitivity and specificity superior to the SBT and a cost much lower than the NGS-NIPT. Thus, from both the test performance and the economic benefit points of views, using the dPCR-NIPT assay to replace the SBT as a primary screen tool followed by the NGS-NIPT rescreen would be a better approach than the existing CS for detection of fetal aneuploidies in maternal plasma.

The Genetic Causes of Nonsyndromic Congenital Retinal Detachment: A Genetic and Phenotypic Study of Pakistani Families.

Purpose: To evaluate consanguineous pedigrees from Pakistan with a clinical diagnosis of nonsyndromic congenital retinal nonattachment (NCRNA) and identify genes responsible for the disease as currently only one NCRNA gene is known (atonal basic helix-loop-helix transcription factor 7: ATOH7). Methods: We implemented a three-step genotyping platform: single nucleotide polymorphism genotyping to identify loss of heterozygosity regions in patients, Retinal Information Network panel screening for mutations in currently known retinal genes. Negative patients were then subjected to whole exome sequencing. Results: We evaluated 21 consanguineous NCRNA pedigrees and identified the causal mutations in known retinal genes in 13 out of our 21 families. We found mutations in ATOH7 in three families. Surprisingly, we then found mutations in familial exudative vitreoretinopathy (FEVR) genes; low-density lipoprotein receptor-related protein 5 mutations (six families), tetraspanin 12 mutations (two families), and NDP mutations (two families). Thus, 62% of the patients were successfully genotyped in our study with seven novel and six previously reported mutations in known retinal genes. Conclusions: Although the clinical diagnosis of all children was NCRNA with severe congenital fibrotic retinal detachments, the molecular diagnosis determined that the disease process was in fact a very severe form of FEVR in 10 families. Because severe congenital retinal detachment has not been previously associated with all the FEVR genes, we have thus expanded the phenotypic spectrum of FEVR, a highly variable retinal detachment phenotype that has clinical overlap with NCRNA. We identified seven novel mutations. We also established for the first time genetic overlap between the Iranian and Pakistani populations. We identified eight NCRNA families that do not harbor mutations in any known retinal genes, suggesting novel causal genes in these families.

Mutations in the unfolded protein response regulator ATF6 cause the cone dysfunction disorder achromatopsia.

Achromatopsia (ACHM) is an autosomal recessive disorder characterized by color blindness, photophobia, nystagmus and severely reduced visual acuity. Using homozygosity mapping and whole-exome and candidate gene sequencing, we identified ten families carrying six homozygous and two compound-heterozygous mutations in the ATF6 gene (encoding activating transcription factor 6A), a key regulator of the unfolded protein response (UPR) and cellular endoplasmic reticulum (ER) homeostasis. Patients had evidence of foveal hypoplasia and disruption of the cone photoreceptor layer. The ACHM-associated ATF6 mutations attenuate ATF6 transcriptional activity in response to ER stress. Atf6(-/-) mice have normal retinal morphology and function at a young age but develop rod and cone dysfunction with increasing age. This new ACHM-related gene suggests a crucial and unexpected role for ATF6A in human foveal development and cone function and adds to the list of genes that, despite ubiquitous expression, when mutated can result in an isolated retinal photoreceptor phenotype.

Novel insights into the molecular pathogenesis of CYP4V2-associated Bietti's retinal dystrophy.

Bietti's crystalline dystrophy (BCD) is a rare, autosomal recessive retinal degenerative disease associated with mutations in CYP4V2. In this study, we describe the genetic and clinical findings in 19 unrelated BCD patients recruited from five international retinal dystrophy clinics. Patients underwent ophthalmic examinations and were screened for CYP4V2 mutations by Sanger sequencing and quantitative polymerase chain reaction (qPCR) copy number variation screening. Eight CYP4V2 mutations were found in 10/19 patients, including three patients in whom only monoallelic mutations were detected. Four novel mutations were identified: c.604G>A; p.(Glu202Lys), c.242C>G; p.(Thr81Arg), c.604+4A>G; p.(?), and c.1249dup; p.(Thr417Asnfs*2). In addition, we identified a heterozygous paternally inherited genomic deletion of at least 3.8 Mb, encompassing the complete CYP4V2 gene and several other genes, which is novel. Clinically, patients demonstrated phenotypic variability, predominantly showing choroidal sclerosis, attenuated vessels, and crystalline deposits of varying degrees of severity. To our knowledge, our study reports the first heterozygous CYP4V2 deletion and hence a novel mutational mechanism underlying BCD. Our results emphasize the importance of copy number screening in BCD. Finally, the identification of CYP4V2-negative patients with indistinguishable phenotypes from CYP4V2-positive patients might suggest the presence of mutations outside the coding regions of CYP4V2, or locus heterogeneity, which is unreported so far.

Choroideremia Is a Systemic Disease With Lymphocyte Crystals and Plasma Lipid and RBC Membrane Abnormalities.

PURPOSE: Photoreceptor neuronal degenerations are common, incurable causes of human blindness affecting 1 in 2000 patients worldwide. Only half of all patients are associated with known mutations in over 250 disease genes, prompting our research program to identify the remaining new genes. Most retinal degenerations are restricted to the retina, but photoreceptor degenerations can also be found in a wide variety of systemic diseases. We identified an X-linked family from Sri Lanka with a severe choroidal degeneration and postulated a new disease entity. Because of phenotypic overlaps with Bietti's crystalline dystrophy, which was recently found to have systemic features, we hypothesized that a systemic disease may be present in this new disease as well. METHODS: For phenotyping, we performed detailed eye exams with in vivo retinal imaging by optical coherence tomography. For genotyping, we performed whole exome sequencing, followed by Sanger sequencing confirmations and cosegregation. Systemic investigations included electron microscopy studies of peripheral blood cells in patients and in normal controls and detailed fatty acid profiles (both plasma and red blood cell [RBC] membranes). Fatty acid levels were compared to normal controls, and only values two standard deviations above or below normal controls were further evaluated. RESULTS: The family segregated a REP1 mutation, suggesting choroideremia (CHM). We then found crystals in peripheral blood lymphocytes and discovered significant plasma fatty acid abnormalities and RBC membrane abnormalities (i.e., elevated plasmalogens). To replicate our discoveries, we expanded the cohort to nine CHM patients, genotyped them for REP1 mutations, and found the same abnormalities (crystals and fatty acid abnormalities) in all patients. CONCLUSIONS: Previously, CHM was thought to be restricted to the retina. We show, to our knowledge for the first time, that CHM is a systemic condition with prominent crystals in lymphocytes and significant fatty acid abnormalities.

Genotype and Phenotype Studies in Autosomal Dominant Retinitis Pigmentosa (adRP) of the French Canadian Founder Population.

PURPOSE: The French Canadian population of Quebec is a unique, well-known founder population with religious, linguistic, and geographic isolation. The genetics of retinitis pigmentosa (RP) in Quebec is not well studied thus far. The purpose of our study was to establish the genetic architecture of autosomal dominant RP (adRP) and to characterize the phenotypes associated with new adRP mutations in Quebec. METHODS: Sanger sequencing of the commonly mutated currently known adRP genes was performed in a clinically well-characterized cohort of 60 adRP French Canadian families. Phenotypes were analyzed by projected visual acuity (best corrected), Goldmann visual fields, optical coherence tomography (OCT), fundus autofluorescence (FAF), and ERG. The potential effect of the novel mutations was assessed using in silico bioinformatic tools. The pathogenicity of all variants was then confirmed by segregation analysis within the families, when available. RESULTS: We identified the causal mutation/gene in 24 of our adRP families, as 24 (40%) of 60 patients had adRP mutations in six known adRP genes. Eleven (46%) of these mutations were in RHO, four mutations (17%) were found in SNRNP200, three mutations (12.5%) in PRPH2/RDS, three mutations (12.5%) in TOPORS, two mutations (8%) in PRPF31, and one mutation (4%) in IMPDH1. Four mutations were novel. We identified new mutations in RHO (p.S270I), PRPF31 (p.R288W), IMPDH1 (p.Q318H), and TOPORS (p.H889R); the rest were previously reported. We present the genotype-phenotype characteristics of the four novel missense mutations. CONCLUSIONS: This is the first large screening of adRP genes in the founder population of Quebec. Our prevalence of known adRP genes is 40% in the French Canadian population, which is lower than in other adRP populations around the world, illustrating the uniqueness of the French Canadian population. Our findings are crucial in expanding the current understanding of the genotypic-phenotypic spectrum of RP and documenting the genetic architecture of our founder population.

Comprehensive analysis of patients with Stargardt macular dystrophy reveals new genotype-phenotype correlations and unexpected diagnostic revisions.

PURPOSE: Stargardt macular dystrophy (STGD) results in early central vision loss. We sought to explain the genetic cause of STGD in a cohort of 88 patients from three different cultural backgrounds. METHODS: Next-generation sequencing using a novel capture panel was used to search for disease-causing mutations. Patients with undetermined causes were clinically reexamined and tested for copy-number variations as well as intronic mutations. RESULTS: We determined the cause of disease in 67% of our patients. Our analysis identified 35 novel ABCA4 alleles. Eleven patients had mutations in genes not previously reported to cause STGD. Finally, 45% of our patients with unsolved causes had single deleterious mutations in ABCA4, a recessive disease gene. No likely pathogenic copy-number variations were identified. CONCLUSION: This study expands our knowledge of STGD by identifying dozens of novel alleles that cause the disease. The frequency of single mutations in ABCA4 among STGD patients is higher than that among controls, indicating that these mutations contribute to disease. Disease in 11 patients was explained by mutations outside ABCA4, underlining the need to genotype all retinal disease genes to maximize genetic diagnostic rates. Few ABCA4 mutations were observed in our French Canadian patients. This population may contain an unidentified founder mutation. Our results indicate that copy-number variations are unlikely to be a major cause of STGD.

A Review of Secondary Photoreceptor Degenerations in Systemic Disease.

Photoreceptor neuronal degenerations are common and incurable causes of human blindness with one in 2000 affected. Approximately, half of all patients are associated with known mutations in more than 200 disease genes. Most retinal degenerations are restricted to the retina (primary retinal degeneration) but photoreceptor degeneration can also be found in a wide variety of systemic and syndromic diseases. These are called secondary retinal degenerations. We review several well-known systemic diseases with retinal degenerations (RD). We discuss RD with hearing loss, RD with brain disease, and RD with musculoskeletal disease. We then postulate which retinal degenerations may also have previously undetected systemic features. Emerging new and exciting evidence is showing that ubiquitously expressed genes associated with multitissue syndromic disorders may also harbor mutations that cause isolated primary retinal degeneration. Examples are RPGR, CEP290, CLN3, MFSD5, and HK1 mutations that cause a wide variety of primary retinal degenerations with intact systems.

A dominant mutation in hexokinase 1 (HK1) causes retinitis pigmentosa.

PURPOSE: To identify the cause of retinitis pigmentosa (RP) in UTAD003, a large, six-generation Louisiana family with autosomal dominant retinitis pigmentosa (adRP). METHODS: A series of strategies, including candidate gene screening, linkage exclusion, genome-wide linkage mapping, and whole-exome next-generation sequencing, was used to identify a mutation in a novel disease gene on chromosome 10q22.1. Probands from an additional 404 retinal degeneration families were subsequently screened for mutations in this gene. RESULTS: Exome sequencing in UTAD003 led to identification of a single, novel coding variant (c.2539G>A, p.Glu847Lys) in hexokinase 1 (HK1) present in all affected individuals and absent from normal controls. One affected family member carries two copies of the mutation and has an unusually severe form of disease, consistent with homozygosity for this mutation. Screening of additional adRP probands identified four other families (American, Canadian, and Sicilian) with the same mutation and a similar range of phenotypes. The families share a rare 450-kilobase haplotype containing the mutation, suggesting a founder mutation among otherwise unrelated families. CONCLUSIONS: We identified an HK1 mutation in five adRP families. Hexokinase 1 catalyzes phosphorylation of glucose to glucose-6-phosphate. HK1 is expressed in retina, with two abundant isoforms expressed at similar levels. The Glu847Lys mutation is located at a highly conserved position in the protein, outside the catalytic domains. We hypothesize that the effect of this mutation is limited to the retina, as no systemic abnormalities in glycolysis were detected. Prevalence of the HK1 mutation in our cohort of RP families is 1%.

Next generation sequencing-based molecular diagnosis of retinitis pigmentosa: identification of a novel genotype-phenotype correlation and clinical refinements.

Retinitis pigmentosa (RP) is a devastating form of retinal degeneration, with significant social and professional consequences. Molecular genetic information is invaluable for an accurate clinical diagnosis of RP due to its high genetic and clinical heterogeneity. Using a gene capture panel that covers 163 of the currently known retinal disease genes, including 48 RP genes, we performed a comprehensive molecular screening in a collection of 123 RP unsettled probands from a wide variety of ethnic backgrounds, including 113 unrelated simplex and 10 autosomal recessive RP (arRP) cases. As a result, 61 mutations were identified in 45 probands, including 38 novel pathogenic alleles. Interestingly, we observed that phenotype and genotype were not in full agreement in 21 probands. Among them, eight probands were clinically reassessed, resulting in refinement of clinical diagnoses for six of these patients. Finally, recessive mutations in CLN3 were identified in five retinal degeneration patients, including four RP probands and one cone-rod dystrophy patient, suggesting that CLN3 is a novel non-syndromic retinal disease gene. Collectively, our results underscore that, due to the high molecular and clinical heterogeneity of RP, comprehensive screening of all retinal disease genes is effective in identifying novel pathogenic mutations and provides an opportunity to discover new genotype-phenotype correlations. Information gained from this genetic screening will directly aid in patient diagnosis, prognosis, and treatment, as well as allowing appropriate family planning and counseling.

Screening of a large cohort of leber congenital amaurosis and retinitis pigmentosa patients identifies novel LCA5 mutations and new genotype-phenotype correlations.

This study was undertaken to investigate the prevalence of sequence variants in LCA5 in patients with Leber congenital amaurosis (LCA), early-onset retinal dystrophy (EORD), and autosomal recessive retinitis pigmentosa (arRP); to delineate the ocular phenotypes; and to provide an overview of all published LCA5 variants in an online database. Patients underwent standard ophthalmic evaluations after providing informed consent. In selected patients, optical coherence tomography (OCT) and fundus autofluorescence imaging were possible. DNA samples from 797 unrelated patients with LCA and 211 with the various types of retinitis pigmentosa (RP) were screened by Sanger sequence analysis of all LCA5 exons and intron/exon junctions. Some LCA patients were prescreened by APEX technology or selected based on homozygosity mapping. In silico analyses were performed to assess the pathogenicity of the variants. Segregation analysis was performed where possible. Published and novel LCA5 variants were collected, amended for their correct nomenclature, and listed in a Leiden Open Variation Database (LOVD). Sequence analysis identified 18 new probands with 19 different LCA5 variants. Seventeen of the 19 LCA5 variants were novel. Except for two missense variants and one splice site variant, all variants were protein-truncating mutations. Most patients expressed a severe phenotype, typical of LCA. However, some LCA subjects had better vision and intact inner segment/outer segment (IS/OS) junctions on OCT imaging. In two families with LCA5 variants, the phenotype was more compatible with EORD with affected individuals displaying preserved islands of retinal pigment epithelium. One of the families with a milder phenotype harbored a homozygous splice site mutation; a second family was found to have a combination of a stop mutation and a missense mutation. This is the largest LCA5 study to date. We sequenced 1,008 patients (797 with LCA, 211 with arRP) and identified 18 probands with LCA5 mutations. Mutations in LCA5 are a rare cause of childhood retinal dystrophy accounting for ∼2% of disease in this cohort, and the majority of LCA5 mutations are likely null. The LCA5 protein truncating mutations are predominantly associated with LCA. However, in two families with the milder EORD, the LCA5 gene analysis revealed a homozygous splice site mutation in one and a stop mutation in combination with a missense mutation in a second family, suggesting that this milder phenotype is due to residual function of lebercilin and expanding the currently known phenotypic spectrum to include the milder early onset RP. Some patients have remaining foveal cone structures (intact IS/OS junctions on OCT imaging) and remaining visual acuities, which may bode well for upcoming treatment trials.

Comprehensive molecular diagnosis of 179 Leber congenital amaurosis and juvenile retinitis pigmentosa patients by targeted next generation sequencing.

BACKGROUND: Leber congenital amaurosis (LCA) and juvenile retinitis pigmentosa (RP) are inherited retinal diseases that cause early onset severe visual impairment. An accurate molecular diagnosis can refine the clinical diagnosis and allow gene specific treatments. METHODS: We developed a capture panel that enriches the exonic DNA of 163 known retinal disease genes. Using this panel, we performed targeted next generation sequencing (NGS) for a large cohort of 179 unrelated and prescreened patients with the clinical diagnosis of LCA or juvenile RP. Systematic NGS data analysis, Sanger sequencing validation, and segregation analysis were utilised to identify the pathogenic mutations. Patients were revisited to examine the potential phenotypic ambiguity at the time of initial diagnosis. RESULTS: Pathogenic mutations for 72 patients (40%) were identified, including 45 novel mutations. Of these 72 patients, 58 carried mutations in known LCA or juvenile RP genes and exhibited corresponding phenotypes, while 14 carried mutations in retinal disease genes that were not consistent with their initial clinical diagnosis. We revisited patients in the latter case and found that homozygous mutations in PRPH2 can cause LCA/juvenile RP. Guided by the molecular diagnosis, we reclassified the clinical diagnosis in two patients. CONCLUSIONS: We have identified a novel gene and a large number of novel mutations that are associated with LCA/juvenile RP. Our results highlight the importance of molecular diagnosis as an integral part of clinical diagnosis.

Next-generation sequencing-based molecular diagnosis of a Chinese patient cohort with autosomal recessive retinitis pigmentosa.

PURPOSE: Retinitis pigmentosa (RP) is a highly heterogeneous genetic disease; therefore, an accurate molecular diagnosis is essential for appropriate disease treatment and family planning. The prevalence of RP in China had been reported at 1 in 3800, resulting in an estimated total of 340,000 Chinese RP patients. However, genetic studies of Chinese RP patients have been very limited. To date, no comprehensive molecular diagnosis has been done for Chinese RP patients. With the emergence of next-generation sequencing (NGS), comprehensive molecular diagnosis of RP is now within reach. The purpose of this study was to perform the first NGS-based comprehensive molecular diagnosis for Chinese RP patients. METHODS: Thirty-one well-characterized autosomal recessive RP (arRP) families were recruited. For each family, the DNA sample from one affected member was sequenced using our custom capture panel, which includes 163 retinal disease genes. Variants were called, filtered, and annotated by our in-house automatic pipeline. RESULTS: Twelve arRP families were successfully molecular diagnosed, achieving a diagnostic rate of approximately 40%. Interestingly, approximately 63% of the pathogenic mutations we identified are novel, which is higher than that observed in a similar study on European descent (45%). Moreover, the clinical diagnoses of two families were refined based on the pathogenic mutations identified in the patients. CONCLUSIONS: We conclude that comprehensive molecular diagnosis can be vital for an accurate clinical diagnosis of RP. Applying this tool on patients from different ethnic groups is essential for enhancing our knowledge of the global spectrum of RP disease-causing mutations.