Functional analysis of germline VANGL2 variants using rescue assays of vangl2 knockout zebrafish.

Developmental studies have shown that the evolutionarily conserved Wnt Planar Cell Polarity (PCP) pathway is essential for the development of a diverse range of tissues and organs including the brain, spinal cord, heart and sensory organs, as well as establishment of the left-right body axis. Germline mutations in the highly conserved PCP gene VANGL2 in humans have only been associated with central nervous system malformations, and functional testing to understand variant impact has not been performed. Here we report three new families with missense variants in VANGL2 associated with heterotaxy and congenital heart disease p.(Arg169His), non-syndromic hearing loss p.(Glu465Ala) and congenital heart disease with brain defects p.(Arg135Trp). To test the in vivo impact of these and previously described variants, we have established clinically-relevant assays using mRNA rescue of the vangl2 mutant zebrafish. We show that all variants disrupt Vangl2 function, although to different extents and depending on the developmental process. We also begin to identify that different VANGL2 missense variants may be haploinsufficient and discuss evidence in support of pathogenicity. Together, this study demonstrates that zebrafish present a suitable pipeline to investigate variants of unknown significance and suggests new avenues for investigation of the different developmental contexts of VANGL2 function that are clinically meaningful.

Biallelic variants in HECT E3 paralogs, HECTD4 and UBE3C, encoding ubiquitin ligases cause neurodevelopmental disorders that overlap with Angelman syndrome.

PURPOSE: Pathogenic variants in genes encoding ubiquitin E3 ligases are known to cause neurodevelopmental syndromes. Additional neurodevelopmental disorders associated with the other genes encoding E3 ligases are yet to be identified. METHODS: Chromosomal analysis and exome sequencing were used to identify the genetic causes in 10 patients from 7 unrelated families with syndromic neurodevelopmental, seizure, and movement disorders and neurobehavioral phenotypes. RESULTS: In total, 4 patients were found to have 3 different homozygous loss-of-function (LoF) variants, and 3 patients had 4 compound heterozygous missense variants in the candidate E3 ligase gene, HECTD4, that were rare, absent from controls as homozygous, and predicted to be deleterious in silico. In 3 patients from 2 families with Angelman-like syndrome, paralog-directed candidate gene approach detected 2 LoF variants in the other candidate E3 ligase gene, UBE3C, a paralog of the Angelman syndrome E3 ligase gene, UBE3A. The RNA studies in 4 patients with LoF variants in HECTD4 and UBE3C provided evidence for the LoF effect. CONCLUSION: HECTD4 and UBE3C are novel biallelic rare disease genes, expand the association of the other HECT E3 ligase group with neurodevelopmental syndromes, and could explain some of the missing heritability in patients with a suggestive clinical diagnosis of Angelman syndrome.

Biallelic loss of function variant in ZNF808 is associated with non-syndromic neonatal diabetes.

A Loss-of-function variant in ZNF808 is associated with non-syndromic neonatal diabetes in a consanguineous family with three affected siblings.

Clinical characterization and further confirmation of the autosomal recessive SLC12A2 disease.

Heterozygous pathogenic variants in SLC12A2 are reported in patients with nonsyndromic hearing loss. Recently, homozygous loss-of-function variants have been reported in two patients with syndromic intellectual disability, with or without hearing loss. However, the clinical and molecular spectrum of SLC12A2 disease has yet to be characterized and confirmed. Using whole-exome sequencing, we detected a homozygous splicing variant in four patients from two independent families with severe developmental delay, microcephaly, respiratory abnormalities, and subtle dysmorphic features, with or without congenital hearing loss. We also reviewed the reported cases with pathogenic variants associated with autosomal dominant and recessive forms of the SLC12A2 disease. About 50% of the cases have syndromic and nonsyndromic congenital hearing loss. All patients harboring the recessive forms of the disease presented with severe global developmental delay. Interestingly, all reported variants are located in the c-terminal domain, suggesting a critical role of this domain for the proper function of the encoded co-transporter protein. In conclusion, our study provides an additional confirmation of the autosomal recessive SLC12A2 disease.

New paradigms of USP53 disease: normal GGT cholestasis, BRIC, cholangiopathy, and responsiveness to rifampicin.

Biallelic variants in the USP53 gene have recently been reported to segregate with normal gamma glutamyltransferase (GGT) cholestasis. Using whole-exome sequencing (WES), we detected two USP53 homozygous variants (c.951delT; p. Phe317fs and c.1744C>T; p. Arg582*) in five additional cases, including an unpublished cousin of a previously described family with intractable itching and normal GGT cholestasis. Three patients, a child and two adults, presented with recurrent episodes of normal GGT cholestasis, consistent with a diagnosis of benign recurrent intrahepatic cholestasis (BRIC). Cholangiopathic changes, possibly autoimmune in origin, were recognized in some patients. Additional phenotypic details in one patient included an enlarged left kidney, and speech/developmental delay. Notably, two patients exhibited a complete response to rifampicin, and one responded to ursodeoxycholic acid (UDCA). Two adult patients were suspected to have autoimmune liver disease and treated with steroids. This report describes new cases of USP53 disease presenting with normal GGT cholestasis or BRIC in three children and two adults. We also describe the novel finding of a dramatic response to rifampicin. The association of cholangiopathy with normal GGT cholestasis provides a diagnostic challenge and remains poorly understood.

Biallelic loss of function variant in the unfolded protein response gene PDIA6 is associated with asphyxiating thoracic dystrophy and neonatal-onset diabetes.

Protein disulfide isomerase A6 (PDIA6) is an unfolded protein response (UPR)-regulating protein. PDIA6 regulates the UPR sensing proteins, Inositol requiring enzyme 1, and EIF2AK3. Biallelic inactivation of the two genes in mice and humans resulted in embryonic lethality, diabetes, skeletal defects, and renal insufficiency. We recently showed that PDIA6 inactivation in mice caused embryonic and early lethality, diabetes and immunodeficiency. Here, we present a case with asphyxiating thoracic dystrophy (ATD) syndrome and infantile-onset diabetes. Whole exome sequencing revealed a homozygous frameshift variant in the PDIA6 gene. RNA expression was reduced in a gene dosage-dependent manner, supporting a loss-of-function effect of this variant. Phenotypic correlation with the mouse model recapitulated the growth defect and delay, early lethality, coagulation, diabetes, immunological, and polycystic kidney disease phenotypes. In general, the phenotype of the current patient is consistent with phenotypes associated with the disruption of PDIA6 and the sensors of UPR in mice and humans. This is the first study to associate ATD to the UPR gene, PDIA6. We recommend screening ATD cases with or without insulin-dependent diabetes for variants in PDIA6.

Clinical, molecular, and biochemical delineation of asparagine synthetase deficiency in Saudi cohort.

PURPOSE: Asparagine synthetase deficiency (ASNSD) is a rare neurometabolic disease. Patients may not demonstrate low asparagine levels, which highlights the advantage of molecular over biochemical testing in the initial work-up of ASNSD. We aimed to further delineate the ASNSD variant and phenotypic spectrum and determine the value of biochemical testing as a frontline investigation in ASNSD. METHODS: We retrospectively collected the clinical and molecular information on 13 families with ASNSD from the major metabolic clinics in Saudi Arabia. RESULTS: The major phenotypes included congenital microcephaly (100%), facial dysmorphism (100%), global developmental delay (100%), brain abnormalities (100%), spasticity (86%), and infantile-onset seizures (93%). Additional unreported phenotypes included umbilical hernia, osteopenia, eczema, lung hypoplasia, and hearing loss. Overall, seven homozygous variants accounted for ASNSD. The p.Tyr398Cys and p.Asn75Ile variants accounted for 54% of the cases. The clinical sensitivity and specificity of the proposed biochemical analysis of cerebrospinal fluid (CSF) for the detection of patients with ASNSD were 83% and 98%, respectively. CONCLUSION: Our study describes the largest reported ASNSD cohort with clinical, molecular, and biochemical characterization. Taking into consideration the suboptimal sensitivity of biochemical screening, the delineation of the phenotype variant spectrum is of diagnostic utility for accurate diagnosis, prognosis, counseling, and carrier screening.

A novel missense variant in the RASGRP2 gene in patients with moderate to severe bleeding disorder.

Inherited platelet function disorder-18 (IPD-18) is a relatively new non-syndromic autosomal recessive bleeding disorder. It is characterized by deficient or dysfunctional CalDAG-GEFI protein. The distinctive feature of the disease is impaired platelet aggregation in response to multiple physiologic agonists. We here report a family with a platelet-type bleeding disorder and a novel mutation in the RASGRP2 gene. The overall bleeding score for the affected individuals was 15 and 12. Based on the initial diagnosis of Glanzmann thrombasthenia, targeted sequencing of integrin subunit alpha 2b and integrin subunit beta 3 encoding genes ITGA2B and ITGB3 were carried out in both affected members of a family. Sequence alignment failed to identify the disease-causing variant(s) in both genes. Therefore, whole exome sequencing in one affected individual was performed. Data analysis detected a novel homozygous missense variant (c.956C>T; p.Pro319Leu) in the exon 9 of the RASGRP2 gene. Five additional individuals of a family including both parents, an affected individual and two asymptomatic individuals were Sanger sequenced for the variant (c.956C>T). The variant segregates in the family in an autosomal recessive manner. Several in silico tools predicted the variant as pathogenic. Protein modeling studies suggest that the mutation (p.Pro319Leu) cause a conformational change in the loop structure of the RasGEF domain of the CalDAG-GEFI protein. Reported variants in the RasGEF domain impair expression and/or nucleotide exchange activity of CalDAG-GEFI protein and thus inhibit the activation of Rap1 protein required for platelet adhesion and hemostatic plug formation.

Exome sequencing identified rare variants in genes HSPG2 and ATP2B4 in a family segregating developmental dysplasia of the hip.

BACKGROUND: Developmental dysplasia of the hip (DDH) is a common pathological condition of the musculoskeletal system in infants which results in a congenital and developmental malformation of the hip joint. DDH is a spectrum of pathologies affecting the infant hip ranging from asymptomatic subtle radiographic signs through mild instability to frank dislocations with acetabular dysplasia. A Saudi family with three affected individuals with DDH was identified and genetic analysis was performed to detect the possible genetic defect(s) underlying DDH in the affected members of the family. METHODS: We performed whole genome genotyping using Illumina HumanOmni 2.5 M array and whole exome sequencing (WES) using Nextera Rapid capture kit and Illumina NextSeq500 instrument in four individuals of a family with DDH. RESULTS: SNP data analysis did not identify any runs of homozygosity and copy number variations. Identity-by-descent (IBD) analysis on whole genome genotyping data identified a shared haplotypes on chromosome 1 in affected individuals. An analysis of the WES data identified rare heterozygous variants in HSPG2 and ATP2B4 genes in the affected individuals. Multiple prediction software predicted that the variants identified are damaging. Moreover, in silico analysis showed that HSPG2 regulates ATP2B4 expression using a variety of transcription factors. CONCLUSION: Our results indicate that there might be a functional epistatic interaction between HSPG2 and ATP2B4, and DDH in the family studied is due to a combined effect of both variants. These variants are also present in the asymptomatic mother suggesting that the variants in HSPG2 and ATP2B4 are incompletely penetrant. This study provides the first evidence of digenic inheritance of DDH in a family and extends the spectrum of genetic heterogeneity in this human disorder.

CIT, a gene involved in neurogenic cytokinesis, is mutated in human primary microcephaly.

Autosomal recessive primary microcephaly (MCPH) is a static neurodevelopmental disorder characterized by congenital small head circumference and non-progressive intellectual disability without additional severe brain malformations. MCPH is a genetically heterogeneous disorder. Sixteen genes (MCPH1-MCPH16) have been discovered so far, mutations thereof lead to autosomal recessive primary microcephaly. In a family, segregating MCPH in an autosomal recessive manner, genome-wide homozygosity mapping mapped a disease locus to 16.9-Mb region on chromosome 12q24.11-q24.32. Following this, exome sequencing in three affected individuals of the family discovered a splice site variant (c.753+3A>T) in citron kinase (CIT) gene, segregating with the disorder in the family. CIT co-localizes to the midbody ring during cytokinesis, and its loss of expression results in defects in neurogenic cytokinesis in both humans and mice. Splice site variant in CIT, identified in this study, is predicted to abolish splice donor site. cDNA sequence of an affected individual showed retention of an intron next to the splice donor site. The study, presented here, revealed the first variant in the CIT causing MCPH in the family.

A Novel Frameshift Mutation in the ITGB3 Gene Leading to Glanzmann's Thrombasthenia in a Saudi Arabian Family.

Glanzmann's thrombasthenia (GT) is an autosomal recessive congenital bleeding disorder of platelet aggregation. Mutations in ITGA2B and ITGB3 genes result in quantitative and/or qualitative abnormalities of the glycoprotein receptor complex IIb/IIIa (integrin αIIbß3), which in turn impairs platelet aggregation and lead to GT. In this study, whole genome single nucleotide polymorphism (SNP) genotyping as well as whole exome sequencing was performed in a large family segregating GT. Analysis of the genotypes localized the disease region to chromosome 17q21.2-q21.3. Filtration of whole exome data and candidate variants prioritization identified a pathogenic variant in the ITGB3 gene. The single nucleotide deletion variant (c.2113delC) in exon 13 of the ITGB3 gene is predicted to cause a frameshift and absence of vital C-terminal domains including the transmembrane helix and the cytoplasmic domain. Clinical variability of the bleeding phenotype in affected individuals with the same mutation suggests that other genetic and nongenetic factors are responsible for determining GT features.

A Biallelic Variant in FRA10AC1 Is Associated With Neurodevelopmental Disorder and Growth Retardation.

Objectives: Our objective was to identify the genetic cause in a family with a remarkable history of neurodevelopmental disease and growth retardation. Methods: A neurologic evaluation was performed, and DNA samples were obtained from the affected siblings and parents to perform whole-exome sequencing (WES). Results: Both siblings presented with dysmorphic features, failure to thrive, global developmental delay, generalized hypotonia, feeding problems, and congenital heart disease. WES revealed a homozygous nonsense variant in the FRA10AC1 gene in both siblings. Discussion: A recent study has reported the first association of biallelic variants in the spliceosomal C complex gene, FRA10AC1, with syndromic neurodevelopmental disease and growth retardation in 5 patients from 3 consanguineous families complex. In this study, we provide the first confirmation of the reported FRA10AC1-related neurologic syndrome in an additional family.

Progressive Ataxia and Neurologic Regression in RFXANK-Associated Bare Lymphocyte Syndrome.

OBJECTIVE: To identify the genetic cause of a late-onset immunodeficiency and subacute progressive neurodegenerative disease affecting cognition, motor, visual, and cerebellar systems in a patient with a family history of 2 younger siblings with an early-onset immunodeficiency disease. METHODS: Physical examinations, immunologic, brain MRI, whole-exome sequencing, and segregation studies were used to identify the genetic and neuroimmunologic etiology of disease in this family. RESULTS: We identified a homozygous loss-of-function (LOF) mutation (c.271+1G>C) in the RFXANK gene in the index patient and one of his younger affected siblings. Biallelic mutations in the RFXANK gene are known to cause bare lymphocyte syndrome (BLS) type II, complementation group B. The clinical and immunologic investigations were consistent with a clinical diagnosis of BLS type II. MRI demonstrated global cerebral and cerebellar atrophy with white matter signal changes in the index case. CONCLUSIONS: In addition to BLS type II, our study has expanded and further characterized the phenotype associated with the LOF of RFXANK to include progressive neurodegenerative disease. Our study also provides evidence for the impact of LOF on brain development and function. Thus, early bone marrow transplantation, as a standard of care for BLS, could prove to be protective against the neurologic phenotypes in this group of patients.

Centromere protein I (CENPI) is a candidate gene for X-linked steroid sensitive nephrotic syndrome.

BACKGROUND: Individuals with proteinuria in association with hypoalbuminemia, edema, and hyperlipidemia are considered as having nephrotic syndrome (NS). NS is the most common kidney disease seen in the paediatric age group. NS is usually classified into steroid resistant nephrotic syndrome (SRNS) and steroid sensitive nephrotic syndrome (SSNS). More than 58 genes have been identified as a monogenic cause of SRNS, however, the genetic architecture of childhood SSNS remains poorly understood. METHODS: Here in this study, we performed sequencing of 66 NS candidate genes followed by whole genome SNP genotyping and whole exome sequencing in SSNS families with multiple affected individuals. RESULTS: NS candidate genes sequencing did not identify any pathogenic variant in the known genes. Homozygosity mapping based on an autosomal recessive model failed to detect any shared loss of heterozygosity region in the genome. An unbiased and hypothesis-free exome data analysis identified a missense variant (c.383G>A; p.Arg128Gln) in the CENPI gene. Sanger sequencing of both parents, unaffected and affected individuals confirmed an X-linked inheritance pattern of the variant (c.383G>A) with SSNS phenotype. The variant (c.383G>A) is very rare and is potentially damaging. CONCLUSION: Collectively, these observations suggest that a specific pathogenic link between SSNS development and alteration in CENPI exists. However, human mutations in CENPI causing SSNS have not been reported hitherto. Identification of genetic defects underlying SSNS will help in understanding the precise aetiology of SSNS and improved management of children with NS.

Whole genome SNP genotyping in a family segregating developmental dysplasia of the hip detected runs of homozygosity on chromosomes 15q13.3 and 19p13.2.

Developmental dysplasia of the hip (DDH) is one of the most prevalent developmental orthopedic diseases worldwide. DDH is a spectrum of anatomical abnormalities of the hip joint and is characterized by premature arthritis in later life. Sporadic cases have been reported more frequently; however, some studies have reported families segregating DDH. Studies have suggested that the genetic factors play a significant role in the development of DDH. In order to detect genetic defect underlying DDH, we performed Sanger sequencing of all DDH associated genes, whole genome SNP genotyping and exome sequencing in a Saudi family with four individuals having DDH. Sanger sequencing of all known genes did not identify any pathogenic variant. Genotype data analysis using HomozygosityMapper identified shared homozygous regions on chromosome 15q13.3 and chromosome 19p13.2 flanked by rs17228178-rs1534200 and rs466123-rs2112461, respectively. These data were also analyzed by cnvpartition software for identification of DDH associated copy number variations (CNV). A shared copy number gain of approximately 15 kb on chr6p21.32 (chr6:33 053 906-33 069 893) was discovered in all affected individuals. Partial gain of this region has also been found in unaffected sibling of this family. Exome data did not reveal any candidate sequence variant. Whole genome sequencing is required to identify deep intronic variants in the shared homozygous regions. Identification of genetic variants involved in pathogenesis of DDH may open up interesting perspectives into the function of the gene(s) in hip joint development.