Novel and recurrent variants in PAX6 in four patients with ocular phenotypes from Southeast Asia.

Aniridia is an autosomal dominant condition characterized by the complete or partial absence of the iris, often with additional presentations such as foveal hypoplasia, nystagmus, cataract, glaucoma and other ocular abnormalities. Most cases are caused by heterozygous mutations in the paired box 6 gene (PAX6), which codes for a transcription factor that regulates eye development. Four patients from our hospital who presented with ocular phenotypes were recruited for research sequencing with informed consent. Sanger sequencing of PAX6 coding exons or exome sequencing was performed on genomic DNA from venous blood samples. Variants in PAX6 were identified in the four patients. Two variants are recurrent single-nucleotide substitutions - one is a substitution found in a patient with bilateral aniridia, whereas the other is a splice variant in a patient with nystagmus and neuroblastoma. The other two variants are novel and found in two patients with isolated aniridia. Both are small duplications that are predicted to lead to premature termination. For the recurrent variants, the comparison of phenotypes for patients with identical variants would shed light on the mechanisms of pathogenesis, and the discovery of two novel variants expands the spectrum of PAX6 mutations.

Novel Variants and Clinical Characteristics of 16 Patients from Southeast Asia with Genetic Variants in Neurofibromin-1.

Neurofibromatosis type 1 (NF1) is one of the most common inherited disorders. It is caused by mutations in the neurofibromin-1 gene ( NF1 ) and affects the formation and growth of nerve tissues. More than 3,600 pathogenic variants in the NF1 gene have been identified from patients with most of the germline variants are from the Western populations. We found 16 patients (15 Chinese and 1 Asian Indian) who had heterozygous variants in NF1 through targeted next-generation sequencing. There were 15 different variants: 4 frameshift, 4 nonsense, 5 missense, and 2 splice variants. One nonsense variant and three frameshift variants had never been reported in any population or patient database. Twelve of the 16 patients met the NF1 diagnostic criteria, and each was found to have a pathogenic or likely pathogenic variant. Three different missense variants of unknown significance were discovered in the other four patients who did not meet NF1 diagnostic criteria. Our findings add four novel variants to the list of genetic mutations linked to NF1's various clinical manifestations.

Novel phenotypic feature in a patient with a recurrent NOTCH2 nonsense mutation.

Pathogenic variants in NOTCH2 which encodes a single-pass transmembrane protein have been identified as a cause of several autosomal dominant congenital disorders. In particular, truncating mutations in exon 34 have been found in patients with skeletal abnormalities and dysmorphic features. We describe a patient with a de novo variant in NOTCH2 who displayed features of both Hajdu-Cheney syndrome (HJCYS) and serpentine fibula-polycystic kidney syndrome (SFPKS). The recurrent nonsense variant in exon 34 has been reported in seven other patients with syndromic presentations, making it the most common pathogenic variant for NOTCH2 in congenital disorders. In addition to the core features of HJCYS and SFPKS, there was a gastrointestinal tract malformation of an imperforate anus which has not been reported in patients with pathogenic variants in NOTCH2.

Biallelic loss-of-function variants in WDR11 are associated with microcephaly and intellectual disability.

Heterozygous missense variants in the WD repeat domain 11 (WDR11) gene are associated with hypogonadotropic hypogonadism in humans. In contrast, knockout of both alleles of Wdr11 in mice results in a more severe phenotype with growth and developmental delay, features of holoprosencephaly, heart defects and reproductive disorders. Similar developmental defects known to be associated with aberrant hedgehog signaling and ciliogenesis have been found in zebrafish after Wdr11 knockdown. We here report biallelic loss-of-function variants in the WDR11 gene in six patients from three independent families with intellectual disability, microcephaly and short stature. The findings suggest that biallelic WDR11 variants in humans result in an overlapping but milder phenotype compared to Wdr11-deficient animals. However, the observed human phenotype differs significantly from dominantly inherited variants leading to hypogonadotropic hypogonadism, suggesting that recessive WDR11 variants result in a clinically distinct entity.

Speckled brain lesions in Incontinentia Pigmenti patients with acquired brain syndromes.

Incontinentia Pigmenti (IP) is a neurocutaneous syndrome, with malformations of cortical development and neurodevelopmental delay in some patients. Neonates with IP may develop acute encephalopathy with multifocal ischemic brain lesions with a speckled pattern on diffusion-weighted magnetic resonance imaging (MRI). We observed a similar MRI pattern in 4 female patients with IP who presented with childhood acute encephalopathy syndromes. These patients, aged 9 days to 13 years old, had acute neonatal encephalitis, Influenza A virus related acute necrotizing encephalopathy (ANE) of childhood, Influenza B virus related acute encephalopathy with biphasic seizures and late restricted diffusion (AESD) and acute disseminated encephalitis (ADEM) with transverse myelitis (TM). These lesions could possibly reflect the white matter changes in IP patients with encephalopathy.

Coffin-Siris Syndrome-1: Report of five cases from Asian populations with truncating mutations in the ARID1B gene.

BACKGROUND: Pathogenic variants of the ARID1B gene are recognized as the most common cause of Coffin-Siris syndrome (CSS) and also one of the most common causes for intellectual disability (ID). Reported ARID1B variants in association with CSS are mostly from patients of European ancestry. METHODS: We performed next-generation sequencing to identify pathogenic variants in patients with congenital disorders from the Genetics clinics. The identified variants were validated by Sanger sequencing. Parental samples were tested by Sanger sequencing to determine inheritance status. RESULTS: Truncating variants in ARID1B were identified in five unrelated Asian patients (one Malay, two Chinese and two Indian) with features of CSS. One was a nonsense mutation which had been documented in three other reports while the other four were novel variants, including two nonsense substitutions and two small deletions resulting in premature termination of translation. Similar to previous reports, all patients have developmental and speech delay, with additional presentations such as ectodermal/facial abnormalities commonly observed in CSS patients. CONCLUSIONS: Our results unveil ARID1B variants in association with CSS in multiple Southeast Asian ethnic groups, and confirm that variants associated with this disorder tend to be of the truncating type. This finding may provide additional insight into the function of the protein and the disease mechanism.

Identification of KMT2D and KDM6A variants by targeted sequencing from patients with Kabuki syndrome and other congenital disorders.

Kabuki syndrome (KS) is a rare congenital disorder characterized by distinctive facies, postnatal growth deficiency, cardiac defects and skeletal anomalies. Studies have determined that pathogenic variants of the lysine-specific methyltransferase 2D (KMT2D) and lysine-specific demethylase 6A (KDM6A) genes are the major causes of KS. The two genes encode different histone-modifying enzymes that are found in the same protein complex that is critical for cell differentiation during development. Here we report the results from next-generation sequencing of genomic DNA from 13 patients who had a clinical diagnosis of KS based on facial dysmorphism and other KS-specific cardinal phenotypes. Nine of the 13 patients were confirmed to be carrying heterozygous pathogenic KMT2D variants, seven of which were truncating and two were missense substitutions. Overall, we uncovered 11 novel variants - nine in KMT2D and two in KDM6A. Seven of the novel variants (all KMT2D) were likely causative of the KS phenotype. Our study expands the number of naturally occurring KMT2D and KDM6A variants. The discovery of novel pathogenic variants will add to the knowledge on disease-causing variants and the relevance of missense variants in KS.

The spectrum of genetic variants and phenotypic features of Southeast Asian patients with Noonan syndrome.

BACKGROUND: Noonan syndrome (NS) is an autosomal dominant disorder that belongs to a group of developmental disorders called RASopathies with overlapping features and multiple causative genes. The aim of the study was to identify mutations underlying this disorder in patients from Southeast Asia and characterize their clinical presentations. METHODS: Patients were identified from the hospital's Genetics clinics after assessment by attending clinical geneticists. A targeted gene panel was used for next-generation sequencing on genomic DNA extracted from the blood samples of 17 patients. RESULTS: Heterozygous missense variants were identified in 13 patients: eight were in PTPN11, three in SOS1, and one each in RIT1 and KRAS. All are known variants that have been reported in patients with NS. Of the 13 patients with identified variants, 10 had short stature, the most common feature for NS. Four of the eight patients with PTPN11 variants had atrial septal defect. Only two had pulmonary stenosis which is reported to be common for PTPN11 mutation carriers. Another two had hypertrophic cardiomyopathy, a feature which is negatively associated with PTPN11 mutations. CONCLUSIONS: Our study provides the mutation and phenotypic spectrum of NS from a new population group. The molecular testing yield of 76% is similar to other studies and shows that the targeted panel approach is useful for identifying genetic mutations in NS which has multiple causative genes. The molecular basis for the phenotypes of the remaining patients remains unknown and would need to be uncovered via sequencing of additional genes or other investigative methods.

PURA syndrome: clinical delineation and genotype-phenotype study in 32 individuals with review of published literature.

BACKGROUND: De novo mutations in PURA have recently been described to cause PURA syndrome, a neurodevelopmental disorder characterised by severe intellectual disability (ID), epilepsy, feeding difficulties and neonatal hypotonia. OBJECTIVES: To delineate the clinical spectrum of PURA syndrome and study genotype-phenotype correlations. METHODS: Diagnostic or research-based exome or Sanger sequencing was performed in individuals with ID. We systematically collected clinical and mutation data on newly ascertained PURA syndrome individuals, evaluated data of previously reported individuals and performed a computational analysis of photographs. We classified mutations based on predicted effect using 3D in silico models of crystal structures of Drosophila-derived Pur-alpha homologues. Finally, we explored genotype-phenotype correlations by analysis of both recurrent mutations as well as mutation classes. RESULTS: We report mutations in PURA (purine-rich element binding protein A) in 32 individuals, the largest cohort described so far. Evaluation of clinical data, including 22 previously published cases, revealed that all have moderate to severe ID and neonatal-onset symptoms, including hypotonia (96%), respiratory problems (57%), feeding difficulties (77%), exaggerated startle response (44%), hypersomnolence (66%) and hypothermia (35%). Epilepsy (54%) and gastrointestinal (69%), ophthalmological (51%) and endocrine problems (42%) were observed frequently. Computational analysis of facial photographs showed subtle facial dysmorphism. No strong genotype-phenotype correlation was identified by subgrouping mutations into functional classes. CONCLUSION: We delineate the clinical spectrum of PURA syndrome with the identification of 32 additional individuals. The identification of one individual through targeted Sanger sequencing points towards the clinical recognisability of the syndrome. Genotype-phenotype analysis showed no significant correlation between mutation classes and disease severity.

Intragenic multi-exon deletion in the FBN1 gene in a child with mildly dilated aortic sinus: a retrotransposal event.

Marfan syndrome is an autosomal dominant disorder affecting mainly the skeletal, ocular and cardiovascular systems. Most cases are caused by mutations in the fibrillin-1 gene (FBN1), although there are some reports on deletions involving FBN1 and other additional genes. We report a male patient who was first evaluated at 4 years of age. Echocardiogram showed a mildly dilated aortic sinus. He also had a history of muscular ventral septal defect which was closed spontaneously and trivial mitral regurgitation. Other phenotypic features include frontal bossing, anteverted ears, joint hyperlaxity, learning disability, skin striae, and height and weight in the >97th centile but no other diagnostic findings of MFS and does not fulfill the revised Ghent criteria. Chromosomal microarray analysis showed a deletion of approximately 36.8 kb at 15q21.1, which starts in intron 6 and ends in intron 9 and includes three FBN1 exons. Sequence analysis of the breakpoint region confirmed the deletion and revealed a concomitant insertion of a retrotransposon within the intron 6/intron 9 region. The intragenic deletion of exons 7-9 was likely the result of a retrotransposition event by a MAST2-SVA element mediated by repetitive sequences.

Next-generation sequencing using a pre-designed gene panel for the molecular diagnosis of congenital disorders in pediatric patients.

BACKGROUND: Next-generation sequencing (NGS) has revolutionized genetic research and offers enormous potential for clinical application. Sequencing the exome has the advantage of casting the net wide for all known coding regions while targeted gene panel sequencing provides enhanced sequencing depths and can be designed to avoid incidental findings in adult-onset conditions. A HaloPlex panel consisting of 180 genes within commonly altered chromosomal regions is available for use on both the Ion Personal Genome Machine (PGM) and MiSeq platforms to screen for causative mutations in these genes. METHODS: We used this Haloplex ICCG panel for targeted sequencing of 15 patients with clinical presentations indicative of an abnormality in one of the 180 genes. Sequencing runs were done using the Ion 318 Chips on the Ion Torrent PGM. Variants were filtered for known polymorphisms and analysis was done to identify possible disease-causing variants before validation by Sanger sequencing. When possible, segregation of variants with phenotype in family members was performed to ascertain the pathogenicity of the variant. RESULTS: More than 97% of the target bases were covered at >20×. There was an average of 9.6 novel variants per patient. Pathogenic mutations were identified in five genes for six patients, with two novel variants. There were another five likely pathogenic variants, some of which were unreported novel variants. CONCLUSIONS: In a cohort of 15 patients, we were able to identify a likely genetic etiology in six patients (40%). Another five patients had candidate variants for which further evaluation and segregation analysis are ongoing. Our results indicate that the HaloPlex ICCG panel is useful as a rapid, high-throughput and cost-effective screening tool for 170 of the 180 genes. There is low coverage for some regions in several genes which might have to be supplemented by Sanger sequencing. However, comparing the cost, ease of analysis, and shorter turnaround time, it is a good alternative to exome sequencing for patients whose features are suggestive of a genetic etiology involving one of the genes in the panel.

A submicroscopic deletion involving part of the CREBBP gene detected by array-CGH in a patient with Rubinstein-Taybi syndrome.

We report a girl with Rubinstein-Taybi syndrome (RSTS) who was found to have copy number loss on 16p13.3 by array-CGH. She has developmental delay and other features of RSTS including downslanting palpebral fissures, a prominent nose with the nasal septum extending below the alae nasi, broad thumbs and big toes, postaxial polydactyly of the right foot and constipation from birth. We report the junction sequence across the breakpoint region for a microdeletion in RSTS. The sequencing results also showed that the deletion was 81.4kb involving three genes DNASE 1, TRAP 1, and CREBBP.

Safety and efficacy of iron chelation therapy with deferiprone in patients with transfusion-dependent thalassemia.

Deferiprone is an orally active iron-chelating agent used in the management of transfusion-related hemosiderosis. It has been in clinical use for over 20 years and has been shown to be effective in reducing cardiac iron load and improving cardiac function. As cardiac siderosis is the leading cause of death in patients with transfusion-dependent thalassemia, deferiprone helps to improve the overall prognosis of these patients. It is relatively well tolerated with gastrointestinal symptoms being the commonest side effects. Agranulocytosis (0.5%), neutropenia (9%), thrombocytopenia (up to 45%) and arthropathy (20%) are the most important side effects and may require discontinuation of therapy. Regular monitoring of blood counts is recommended for patients on deferiprone therapy.