Confirmation and pathogenicity of small copy number variations incidentally detected via a targeted next-generation sequencing-based PGT-A platform.

OBJECTIVE: To evaluate the technical accuracy, inheritance, and pathogenicity of small copy number variants (CNVs) detected by a targeted next-generation sequencing (NGS)-based PGT-A platform. DESIGN: Retrospective observational study performed between 2020-2022. SUBJECTS: 12,157 patients who underwent clinical PGT-A performed by targeted NGS for whole chromosome and large segmental aneuploidies. EXPOSURE: An incidental finding was reported when a CNV gain/loss of at least three consecutive amplicons appeared in at least two embryos from the same IVF cycle. MAIN OUTCOME MEASURES: The primary outcome measures were the specificity, incidence, inheritance, and pathogenicity of small CNVs detected by the PGT-A platform. Accuracy of the PGT-A platform CNV calls was assessed via concordance with the CNV calls (size and genomic location) on chromosomal microarray of the gamete provider(s). Parental origin of the CNV and pathogenicity classifications were also reported. RESULTS: In 75 of 12,157 unique PGT-A patients (0.62%;95%CI:0.5-0.8%), an incidental finding that met reporting criteria was identified. Chromosomal microarray follow-up was requested for all cases and results were received for one or both members of 65 reproductive couples. In all cases, one of the gamete providers was confirmed to have the CNV identified in the embryos (100.0%: N=65/65 95%CI:94.5-100). The identified CNV was of maternal origin in 34 cases (52.3%) and of paternal origin in 31 cases (47.7%). A significant correlation was identified between PGT-A-predicted CNV sizes and chromosomal microarray detected sizes (r=0.81) and genomic coordinates on parental DNA. Twenty-six (40%) of the CNVs were classified as benign/likely benign, 30 (46.2%) as a variant of uncertain significance (VUS), and 9 (13.8%) as pathogenic/likely pathogenic. CONCLUSION: Certain PGT-A platforms may enable the detection of inherited, small CNVs with extremely high specificity without prior knowledge of parental status. The majority of CNVs in this data set were confirmed to be benign/likely benign or a VUS; however, pathogenic/likely pathogenic CNVs associated with a broad range of phenotypic features may also be detected, although a reliable negative predictive value for small CNVs with current PGT-A technologies is unknown due to the many technical challenges.

Limits imposed by the experimental design of a large prospective non-inferiority study on PGT-A invalidate many of the conclusions.

The New England Journal of Medicine recently published a large study addressing the efficacy of preimplantation genetic testing for aneuploidy (PGT-A). The 14-centre randomized control non-inferiority trial used cumulative live birth rate (CLBR) as a clinical endpoint to examine the value of PGT-A and concluded that conventional IVF was not inferior to IVF with PGT-A. Unfortunately, the experimental design was highly flawed; and in fact, the data generated in the study do not support the major conclusions presented in the publication. The embryos in each patient's three-embryo pool, which were available for transfer, were selected solely by morphology. The investigators then randomized patients to either the PGT-A group or the control group. It is important to note that PGT-A screening in the study group was done only after the embryos were selected. PGT-A was not really used in a meaningful way, which would have been for the PGT-A results to help in selecting which embryos would be in the three-embryo group. Thus, the outcomes were wholly determined prior to the study intervention. The ultimate delivery rate for each group of three embryos was determined when they were selected by morphology. The randomization, which occurred after embryo selection, would assure equal distribution of those cohorts destined to deliver and those destined to fail to the two study groups, the PGT-A and control groups. Thus, there was no potential for PGT-A to enhance selection and thus no possible way to improve the cumulative outcomes. Since there was no possible way for the control group to be inferior, the experimental design precluded any chance of evaluating the primary endpoint of the study. The primary question of the study was never evaluated. Another serious flaw was that the study was initiated prior to knowing how to interpret the data provided in the PGT-A analytical result. Specifically, the design excluded mosaic embryos from transfer despite the literature demonstrating the significant reproductive potential for these embryos. When accounting for the lost deliveries induced by this non-evidence-based decision, the expected delivery rates in the two groups become virtually identical. That is an important issue because the data from the study actually demonstrate the safety of PGT-A without diminution in outcomes from the impact of trophectoderm biopsy or the discarding of competent embryos which had wrongfully been considered aneuploid. A final serious flaw in the experimental design and interpretation of the data surrounding the issue of the miscarriage rate. The investigators noted that the miscarriage rate was lower in the PGT-A group but stated that its impact was insufficient to alter the CLBR. Of course, by design, the CLBRs were limited to being equivalent. There was no potential for enhanced outcomes in the PGT-A group and thus no possibility that the lower risk of miscarriage in the PGT-A group would raise the CLBR. The benefit of a lower miscarriage rate is real and significant. Its relevance should not be diminished based on the lack of a change in the CLBR since that was never possible in this study. The investigators of the study concluded that the CLBR with conventional ART is equivalent to that with PGT-A, but a simple review of the experiment reassigns their genuine findings to those of a safety study. Significantly, the data in the study demonstrate that the intervention of PGT-A is safe. This study neither supports nor refutes the efficacy of clinical PGT-A.

On the reproductive capabilities of aneuploid human preimplantation embryos.

In IVF cycles, the application of aneuploidy testing at the blastocyst stage is quickly growing, and the latest reports estimate almost half of cycles in the US undergo preimplantation genetic testing for aneuploidies (PGT-A). Following PGT-A cycles, understanding the predictive value of an aneuploidy result is paramount for making informed decisions about the embryo's fate and utilization. Compelling evidence from non-selection trials strongly supports that embryos diagnosed with a uniform whole-chromosome aneuploidy very rarely result in the live birth of a healthy baby, while their transfer exposes women to significant risks of miscarriage and chromosomally abnormal pregnancy. On the other hand, embryos displaying low range mosaicism for whole chromosomes have shown reproductive capabilities somewhat equivalent to uniformly euploid embryos, and they have comparable clinical outcomes and gestational risks. Therefore, given their clearly distinct biological origin and clinical consequences, careful differentiation between uniform and mosaic aneuploidy is critical in both the clinical setting when counseling individuals and in the research setting when presenting aneuploidy studies in human embryology. Here, we focus on the evidence gathered so far on PGT-A diagnostic predictive values and reproductive outcomes observed across the broad spectrum of whole-chromosome aneuploidies detected at the blastocyst stage to obtain evidence-based conclusions on the clinical management of aneuploid embryos in the quickly growing PGT-A clinical setting.

The concordance rates of an initial trophectoderm biopsy with the rest of the embryo using PGTseq, a targeted next-generation sequencing platform for preimplantation genetic testing-aneuploidy.

OBJECTIVE: To determine how often the results of a single trophectoderm (TE) biopsy tested by PGTseq, a targeted next-generation sequencing preimplantation genetic testing for aneuploidy technology, reflect the biology of the rest of the embryo. DESIGN: Blinded prospective cohort study. SETTING: University-affiliated private practice. PATIENT(S): A total of 300 blastocysts were donated; 113 of these embryos were euploid; 163 embryos possessed at least one whole chromosome aneuploidy; and 24 embryos were negative for whole chromosome aneuploidy but possessed at least one secondary finding on initial TE biopsy. INTERVENTION(S): All blastocysts underwent rebiopsy and preimplantation genetic testing for aneuploidy on the PGTseq platform. MAIN OUTCOME MEASURE(S): Partial concordance rate per embryo, total concordance rate per embryo, and total concordance rate per chromosomal event. RESULT(S): An initial TE biopsy result of euploidy or whole chromosome aneuploidy was reconfirmed in >99% of rebiopsied samples, affirming that meiotic errors are manifested in almost the entire embryo. In contrast, results of whole chromosome or segmental mosaicism were confirmed in 15%-18% of subsequent rebiopsies, suggesting that mitotic events are only sporadically seen throughout the embryo. Segmental aneuploidy was confirmed in 56.6% of rebiopsied samples, identifying a mixed meiotic and mitotic etiology for such abnormalities. CONCLUSION(S): A euploid or aneuploid result on the PGTseq platform is highly concordant with the rest of the embryo's ploidy status. The rarer confirmation of whole chromosome mosaic and segmental mosaic results suggest that these mosaics are suitable for embryo transfer. Segmental aneuploidy, with higher concordance rates throughout the embryo, may represent a different biologic etiology compared to mosaic embryos.

Noninvasive preimplantation genetic testing for aneuploidy exhibits high rates of deoxyribonucleic acid amplification failure and poor correlation with results obtained using trophectoderm biopsy.

OBJECTIVE: To validate a commercially available noninvasive preimplantation genetic testing for aneuploidy (niPGT-A) assay by investigating the following: prevalence of deoxyribonucleic acid (DNA) amplification failure with niPGT-A; factors affecting amplification failure with niPGT-A; and frequency of discordant results between niPGT-A and traditional preimplantation genetic testing for aneuploidy. DESIGN: Prospective cohort study SETTING: Academic-affiliated private practice PATIENT(S): One hundred sixty-six blastocysts and their surrounding culture media from couples undergoing in vitro fertilization between July 2019 and May 2020 were analyzed. INTERVENTION(S): Blastocyst-stage spent culture media samples underwent niPGT-A using a commercially available kit that used whole-genome amplification with a modified multiple annealing and looping-based amplification cycle protocol followed by next-generation sequencing. Preimplantation genetic testing for aneuploidy of trophectoderm (TE) biopsies was performed using targeted next-generation sequencing. MAIN OUTCOME MEASURE(S): The primary outcome was failure to achieve an interpretable result with niPGT-A. Factors affecting DNA amplification were also assessed. Discrepancies between niPGT-A and TE biopsy results were analyzed, and clinical outcomes were evaluated. RESULT(S): Deoxyribonucleic acid amplification failures with niPGT-A were observed in 37.3% (62/166) of the samples. With TE biopsy, no embryos exhibited DNA amplification failure. Embryos with a shorter duration of exposure to the culture media and no evidence of whole-chromosome aneuploidy on the TE biopsy displayed high rates of DNA amplification failure with niPGT-A. Of 104 embryos with both niPGT-A and TE biopsy results available, whole-chromosome discordance was noted in 42 cases (40.4%). Three embryos classified as aneuploid based on the niPGT-A result progressed to successful delivery. CONCLUSION(S): The rates of DNA amplification failure were high among the niPGT-A samples, virtually precluding the clinical applicability of niPGT-A in its current form.

A multicenter, prospective, blinded, nonselection study evaluating the predictive value of an aneuploid diagnosis using a targeted next-generation sequencing-based preimplantation genetic testing for aneuploidy assay and impact of biopsy.

OBJECTIVE: To determine the predictive value of an aneuploid diagnosis with a targeted next-generation sequencing-based preimplantation genetic testing for aneuploidy (PGT-A) assay in prognosticating the failure of a successful delivery. DESIGN: Prospective, blinded, multicenter, nonselection study. All usable blastocysts were biopsied, and the single best morphologic blastocyst was transferred before genetic analysis. Preimplantation genetic testing for aneuploidy was performed after clinical outcome was determined. Clinical outcomes were compared to PGT-A results to calculate the predictive value of a PGT-A aneuploid diagnosis. SETTING: Fertility centers. PATIENT(S): Couples undergoing their first in vitro fertilization cycle without recurrent pregnancy loss, antral follicle count < 8, or body mass index ≥ 35 kg/m2. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): The primary outcome was the ability of the analytical result of aneuploid to predict failure to deliver (clinical result). A secondary outcome was the impact of the trophectoderm biopsy on sustained implantation. RESULT(S): Four hundred two patients underwent 484 single, frozen, blastocyst transfers. The PGT-A aneuploid diagnosis clinical error rate was 0%. There was no difference in sustained implantation between the study group and an age-matched control group, where biopsy was not performed (47.9% vs. 45.8). CONCLUSION(S): The PGT-A assay evaluated was highly prognostic of failure to deliver when an aneuploid result was obtained. Additionally, the trophectoderm biopsy had no detectable adverse impact on sustained implantation. CLINICAL TRIAL REGISTRATION NUMBERS: NCT02032264 and NCT03604107.

Key metrics and processes for validating embryo diagnostics.

Embryo diagnostics are somewhat controversial in clinical assisted reproduction technology (ART) practice and remain an active area of investigation. Application of embryo diagnostics holds great potential to raise the standard of clinical care by eliminating futile transfers, allowing highly effective single-embryo transfer, and reducing the probability of clinical loss and ongoing abnormal gestations. These advantages are accompanied by risks, principally the chance that a reproductively competent embryo will be mislabeled and discarded. This would lower the ultimate probability that one or more of the embryos might implant and lead to delivery of a healthy infant. Rigorous validation should be required for embryo diagnostics. Metrics for validation can be divided into three simple areas: analytical validation, determination of clinical predictive values for normal and abnormal test results, and a randomized clinical trial to demonstrate that the selection advantage gained through the diagnostic improves clinical outcomes.

Biallelic variants in AGTPBP1, involved in tubulin deglutamylation, are associated with cerebellar degeneration and motor neuropathy.

The ATP/GTP-Binding Protein 1 (AGTPBP1) gene (OMIM *606830) catalyzes deglutamylation of polyglutamylated proteins, and its deficiency manifests by cerebellar ataxia and peripheral neuropathy in mice and lower motor neuron-like disease in sheep. In the mutant mice, cerebellar atrophy due to Purkinje cell degeneration is observed, likely due to increased tubulin polyglutamylation in affected brain areas. We report two unrelated individuals who presented with early onset cerebellar atrophy, developmental arrest with progressive muscle weakness, and feeding and respiratory difficulties, accompanied by severe motor neuronopathy. Whole exome sequencing followed by segregation analysis in the families and cDNA studies revealed deleterious biallelic variants in the AGTPBP1 gene. We conclude that complete loss-of-function of AGTPBP1 in humans, just like in mice and sheep, is associated with cerebellar and motor neuron disease, reminiscent of Pontocerebellar Hypoplasia Type 1 (PCH1).

Molecular Testing for Preimplantation Genetic Diagnosis of Single Gene Disorders.

Preimplantation genetic testing has evolved tremendously from the early days of FISH detection for a select few chromosome aneuploidies to now combining the detection of all whole chromosome imbalances in conjunction with single gene disorder testing for inherited diseases. As universal carrier screening and exome or genome studies become more commonplace, more and more families are becoming interested in reducing the risk of having a child with a severe disease using preimplantation genetic testing. We describe here the use of quantitative PCR (qPCR) for the custom construction of single gene disorder testing plans for families, the validation of the probes designed, and the protocol for diagnosing an embryo biopsy. qPCR has been shown to have the lowest risk of failed amplification and allele dropout and thus the lowest risk of a misdiagnosis, while also currently providing the fastest protocol to allow for rapid turnaround of results.

USMG5 Ashkenazi Jewish founder mutation impairs mitochondrial complex V dimerization and ATP synthesis.

Leigh syndrome is a frequent, heterogeneous pediatric presentation of mitochondrial oxidative phosphorylation (OXPHOS) disease, manifesting with psychomotor retardation and necrotizing lesions in brain deep gray matter. OXPHOS occurs at the inner mitochondrial membrane through the integrated activity of five protein complexes, of which complex V (CV) functions in a dimeric form to directly generate adenosine triphosphate (ATP). Mutations in several different structural CV subunits cause Leigh syndrome; however, dimerization defects have not been associated with human disease. We report four Leigh syndrome subjects from three unrelated Ashkenazi Jewish families harboring a homozygous splice-site mutation (c.87 + 1G>C) in a novel CV subunit disease gene, USMG5. The Ashkenazi population allele frequency is 0.57%. This mutation produces two USMG5 transcripts, wild-type and lacking exon 3. Fibroblasts from two Leigh syndrome probands had reduced wild-type USMG5 mRNA expression and undetectable protein. The mutation did not alter monomeric CV expression, but reduced both CV dimer expression and ATP synthesis rate. Rescue with wild-type USMG5 cDNA in proband fibroblasts restored USMG5 protein, increased CV dimerization and enhanced ATP production rate. These data demonstrate that a recurrent USMG5 splice-site founder mutation in the Ashkenazi Jewish population causes autosomal recessive Leigh syndrome by reduction of CV dimerization and ATP synthesis.

A homozygous deleterious CDK10 mutation in a patient with agenesis of corpus callosum, retinopathy, and deafness.

The primary cilium is a key organelle in numerous physiological and developmental processes. Genetic defects in the formation of this non-motile structure, in its maintenance and function, underlie a wide array of ciliopathies in human, including craniofacial, brain and heart malformations, and retinal and hearing defects. We used exome sequencing to study the molecular basis of disease in an 11-year-old female patient who suffered from growth retardation, global developmental delay with absent speech acquisition, agenesis of corpus callosum and paucity of white matter, sensorineural deafness, retinitis pigmentosa, vertebral anomalies, patent ductus arteriosus, and facial dysmorphism reminiscent of STAR syndrome, a suspected ciliopathy. A homozygous variant, c.870_871del, was identified in the CDK10 gene, predicted to cause a frameshift, p.Trp291Alafs*18, in the cyclin-dependent kinase 10 protein. CDK10 mRNAs were detected in patient cells and do not seem to undergo non-sense mediated decay. CDK10 is the binding partner of Cyclin M (CycM) and CDK10/CycM protein kinase regulates ciliogenesis and primary cilium elongation. Notably, CycM gene is mutated in patients with STAR syndrome. Following incubation, the patient cells appeared less elongated and more densely populated than the control cells suggesting that the CDK10 mutation affects the cytoskeleton. Upon starvation and staining with acetylated-tubulin, γ-tubulin, and Arl13b, the patient cells exhibited fewer and shorter cilia than control cells. These findings underscore the importance of CDK10 for the regulation of ciliogenesis. CDK10 defect is likely associated with a new form of ciliopathy phenotype; additional patients may further validate this association.

Mutations in TMEM260 Cause a Pediatric Neurodevelopmental, Cardiac, and Renal Syndrome.

Despite the accelerated discovery of genes associated with syndromic traits, the majority of families affected by such conditions remain undiagnosed. Here, we employed whole-exome sequencing in two unrelated consanguineous kindreds with central nervous system (CNS), cardiac, renal, and digit abnormalities. We identified homozygous truncating mutations in TMEM260, a locus predicted to encode numerous splice isoforms. Systematic expression analyses across tissues and developmental stages validated two such isoforms, which differ in the utilization of an internal exon. The mutations in both families map uniquely to the long isoform, raising the possibility of an isoform-specific disorder. Consistent with this notion, RT-PCR of lymphocyte cell lines from one of the kindreds showed reduced levels of only the long isoform, which could be ameliorated by emetine, suggesting that the mutation induces nonsense-mediated decay. Subsequent in vivo testing supported this hypothesis. First, either transient suppression or CRISPR/Cas9 genome editing of zebrafish tmem260 recapitulated key neurological phenotypes. Second, co-injection of morphants with the long human TMEM260 mRNA rescued CNS pathology, whereas the short isoform was significantly less efficient. Finally, immunocytochemical and biochemical studies showed preferential enrichment of the long TMEM260 isoform to the plasma membrane. Together, our data suggest that there is overall reduced, but not ablated, functionality of TMEM260 and that attenuation of the membrane-associated functions of this protein is a principal driver of pathology. These observations contribute to an appreciation of the roles of splice isoforms in genetic disorders and suggest that dissection of the functions of these transcripts will most likely inform pathomechanism.

Identification of a novel pathogenic OTOF variant causative of nonsyndromic hearing loss with high frequency in the Ashkenazi Jewish population.

Mutations in the OTOF gene have previously been shown to cause nonsyndromic prelingual deafness (DFNB9, OMIM 601071) as well as auditory neuropathy/dys-synchrony. In this study, the OTOF NM_194248.2 c.5332G>T, p.Val1778Phe variant was identified in a large Ashkenazi Jewish family as the causative variant in four siblings with hearing loss. Our analysis reveals a carrier frequency of the OTOF c.5332G>T, p.Val1778Phe variant of 1.27% in the Ashkenazi Jewish population, suggesting that this variant may be a significant contributor to nonsyndromic sensorineural hearing loss and should be considered for inclusion in targeted hearing loss panels for this population. Of note, the degree of hearing loss associated with this phenotype ranged from mild to moderately severe, with two of the four siblings not known to have hearing loss until they were genotyped and underwent pure tone audiometry and auditory brainstem response testing. The phenotypic variability along with the auditory neuropathy/dys-synchrony, which allows for the production of otoacoustic emissions, supports that nonsyndromic hearing loss caused by OTOF mutations may be much more common in the Ashkenazi Jewish population than currently appreciated due to a lack of diagnosis.

A mutation in the THG1L gene in a family with cerebellar ataxia and developmental delay.

Autosomal-recessive cerebellar atrophy is usually associated with inactivating mutations and early-onset presentation. The underlying molecular diagnosis suggests the involvement of neuronal survival pathways, but many mechanisms are still lacking and most patients elude genetic diagnosis. Using whole exome sequencing, we identified homozygous p.Val55Ala in the THG1L (tRNA-histidine guanylyltransferase 1 like) gene in three siblings who presented with cerebellar signs, developmental delay, dysarthria, and pyramidal signs and had cerebellar atrophy on brain MRI. THG1L protein was previously reported to participate in mitochondrial fusion via its interaction with MFN2. Abnormal mitochondrial fragmentation, including mitochondria accumulation around the nuclei and confinement of the mitochondrial network to the nuclear vicinity, was observed when patient fibroblasts were cultured in galactose containing medium. Culturing cells in galactose containing media promotes cellular respiration by oxidative phosphorylation and the action of the electron transport chain thus stimulating mitochondrial activity. The growth defect of the yeast thg1Δ strain was rescued by the expression of either yeast Thg1 or human THG1L; however, clear growth defect was observed following the expression of the human p.Val55Ala THG1L or the corresponding yeast mutant. A defect in the protein tRNAHis guanylyltransferase activity was excluded by the normal in vitro G-1 addition to either yeast tRNAHis or human mitochondrial tRNAHis in the presence of the THG1L mutation. We propose that homozygosity for the p.Val55Ala mutation in THG1L is the cause of the abnormal mitochondrial network in the patient fibroblasts, likely by interfering with THG1L activity towards MFN2. This may result in lack of mitochondria in the cerebellar Purkinje dendrites, with degeneration of Purkinje cell bodies and apoptosis of granule cells, as reported for MFN2 deficient mice.

SNP array-based analyses of unbalanced embryos as a reference to distinguish between balanced translocation carrier and normal blastocysts.

PURPOSE: The purpose of the study is to validate a method that provides the opportunity to distinguish a balanced translocation carrier embryo from a truly normal embryo in parallel with comprehensive chromosome screening (CCS). METHODS: A series of translocation carrier couples that underwent IVF with single nucleotide polymorphism (SNP) array-based CCS on 148 embryos were included. Predictions of balanced or normal status of each embryo were made based upon embryonic SNP genotypes. In one case, microdeletion status was used to designate whether embryos were balanced or normal. In 10 additional cases, conventional karyotyping was performed on newborns in order to establish the true genetic status (balanced or normal) of the original transferred embryo. Finally, implantation potential of balanced or normal embryos was compared. RESULTS: Phasing SNPs using unbalanced embryos allowed accurate prediction of whether transferred embryos were balanced translocation carriers or truly normal in all cases completed to date (100 % concordance with conventional karyotyping of newborns). No difference in implantation potential of balanced or normal embryos was observed. CONCLUSIONS: This study demonstrates the validity of a CCS method capable of distinguishing normal from balanced translocation carrier embryos. The only prerequisite is the availability of parental DNA and an unbalanced IVF embryo, making the method applicable to the majority of carrier couples. In addition, the SNP array platform allows simultaneous CCS for aneuploidy with the same platform and from the same biopsy. Future work will involve prospective predictions to select normal embryos with subsequent karyotyping of the resulting newborns.

Deficiency of HTRA2/Omi is associated with infantile neurodegeneration and 3-methylglutaconic aciduria.

BACKGROUND: Cell survival critically depends on the integrity of mitochondria, which play a pivotal role during apoptosis. Extensive mitochondrial damage promotes release of pro-apoptotic factors from the intermembrane space of mitochondria. Released mitochondrial proteins include Smac/DIABLO and HTRA2/Omi, which inhibit the cytosolic E3 ubiquitin ligase XIAP and other inhibitors of apoptosis proteins. AIMS: Here we investigated the cause of extreme hypertonia at birth, alternating with hypotonia, with the subsequent appearance of extrapyramidal symptoms, lack of psychomotor development, microcephaly, intractable seizures and early death in four patients from two unrelated families. The patients showed lactic acidemia, 3-methylglutaconic aciduria, intermittent neutropenia, evolving brain atrophy and disturbed cristae structure in muscle mitochondria. METHODS AND RESULTS: Using whole-exome sequencing, we identified missplicing mutation and a 5 bp deletion in HTRA2, encoding HTRA2/Omi. This protein was completely absent from the patients' fibroblasts, whose growth was impaired and which were hypersensitive to apoptosis. Expression of HtrA2/Omi or of the proteolytically inactive HTRA2/Omi protein restored the cells' apoptotic resistance. However, cell growth was only restored by the proteolytically active protein. CONCLUSIONS: This is the first report of recessive deleterious mutations in HTRA2 in human. The clinical phenotype, the increased apoptotic susceptibility and the impaired cell growth recapitulate those observed in the Htra2 knockout mice and in mutant mice with proteolytically inactive HTRA2/Omi. Together, they underscore the importance of both chaperone and proteolytic activities of HTRA2/Omi for balanced apoptosis sensitivity and for brain development. Absence of HTRA2/Omi is associated with severe neurodegenerative disorder of infancy, abnormal mitochondria, 3-methylglutaconic aciduria and increased sensitivity to apoptosis.

Deficiency of the alkaline ceramidase ACER3 manifests in early childhood by progressive leukodystrophy.

BACKGROUND/AIMS: Leukodystrophies due to abnormal production of myelin cause extensive morbidity in early life; their genetic background is still largely unknown. We aimed at reaching a molecular diagnosis in Ashkenazi-Jewish patients who suffered from developmental regression at 6-13 months, leukodystrophy and peripheral neuropathy. METHODS: Exome analysis, determination of alkaline ceramidase activity catalysing the conversion of C18:1-ceramide to sphingosine and D-ribo-C12-N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl) (NBD)-phytoceramide to NBD-C12-fatty acid using liquid chromatography-tandem mass spectrometry (LC-MS/MS) and thin layer chromatography, respectively, and sphingolipid analysis in patients' blood by LC-MS/MS. RESULTS: The patients were homozygous for p.E33G in the ACER3, which encodes a C18:1-alkaline ceramidase and C20:1-alkaline ceramidase. The mutation abolished ACER3 catalytic activity in the patients' cells and failed to restore alkaline ceramidase activity in yeast mutant strain. The levels of ACER3 substrates, C18:1-ceramides and dihydroceramides and C20:1-ceramides and dihydroceramides and other long-chain ceramides and dihydroceramides were markedly increased in the patients' plasma, along with that of complex sphingolipids, including monohexosylceramides and lactosylceramides. CONCLUSIONS: Homozygosity for the p.E33G mutation in the ACER3 gene results in inactivation of ACER3, leading to the accumulation of various sphingolipids in blood and probably in brain, likely accounting for this new form of childhood leukodystrophy.

Development and validation of concurrent preimplantation genetic diagnosis for single gene disorders and comprehensive chromosomal aneuploidy screening without whole genome amplification.

OBJECTIVE: To develop a novel and robust protocol for multifactorial preimplantation genetic testing of trophectoderm biopsies using quantitative polymerase chain reaction (qPCR). DESIGN: Prospective and blinded. SETTING: Not applicable. PATIENT(S): Couples indicated for preimplantation genetic diagnosis (PGD). INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): Allele dropout (ADO) and failed amplification rate, genotyping consistency, chromosome screening success rate, and clinical outcomes of qPCR-based screening. RESULT(S): The ADO frequency on a single cell from a fibroblast cell line was 1.64% (18/1,096). When two or more cells were tested, the ADO frequency dropped to 0.02% (1/4,426). The rate of amplification failure was 1.38% (55/4,000) overall, with 2.5% (20/800) for single cells and 1.09% (35/3,200) for samples that had two or more cells. Among 152 embryos tested in 17 cases by qPCR-based PGD and CCS, 100% were successfully given a diagnosis, with 0% ADO or amplification failure. Genotyping consistency with reference laboratory results was >99%. Another 304 embryos from 43 cases were included in the clinical application of qPCR-based PGD and CCS, for which 99.7% (303/304) of the embryos were given a definitive diagnosis, with only 0.3% (1/304) having an inconclusive result owing to recombination. In patients receiving a transfer with follow-up, the pregnancy rate was 82% (27/33). CONCLUSION(S): This study demonstrates that the use of qPCR for PGD testing delivers consistent and more reliable results than existing methods and that single gene disorder PGD can be run concurrently with CCS without the need for additional embryo biopsy or whole genome amplification.

Leukoencephalopathy and early death associated with an Ashkenazi-Jewish founder mutation in the Hikeshi gene.

BACKGROUND: Leukodystrophies are genetic white matter disorders affecting the formation or maintenance of myelin. Among the recently discovered genetic defects associated with leukodystrophies, several genes converge on a common mechanism involving protein transcription/translation and ER stress response. METHODS: The genetic basis of a novel congenital leukodystrophy, associated with early onset spastic paraparesis, acquired microcephaly and optic atrophy was studied in six patients from three unrelated Ashkenazi-Jewish families. To this end we used homozygosity mapping, exome analysis, western blot (Hikeshi, HSF1-pS326 and b-actin) in patient fibroblasts, indirect immunofluorescence (HSP70 and HSF1) in patient fibroblasts undergoing heat shock stress, nuclear injection of plasmids expressing Hikeshi or EGFP in patient fibroblasts, in situ hybridization and Immunoblot analysis of Hikeshi in newborn and adult mouse brain. RESULTS: All the patients were homozygous for a missense mutation, p.Val54Leu, in C11ORF73 encoding HSP70 nuclear transporter protein, Hikeshi. The mutation segregated with the disease in the families and was carried by 1:200 Ashkenazi-Jewish individuals. The mutation was associated with undetectable level of Hikeshi in the patients' fibroblasts and with lack of nuclear HSP70 during heat shock stress, a phenomenon which was reversed upon the introduction of normal human Hikeshi to the patients cells. Hikeshi was found to be expressed in central white matter of mouse brain. CONCLUSIONS: These data underscore the importance of Hikeshi for HSP70 relocation into the nucleus. It is likely that in the absence of Hikeshi, HSP70 cannot attenuate the multiple heat shock induced nuclear phenotypes, leaving the cells unprotected during heat shock stress. We speculate that the sudden death of three of the six patients following a short febrile illness and the life-threatening myo-pericarditis in the fourth are the result of excess extra-nuclear HSP70 level which initiates cytokine release or provide target for natural killer cells. Alternatively, nuclear HSP70 might play an active role in stressed cells protection.