Exome sequencing identifies pathogenic variants of VPS13B in a patient with familial 16p11.2 duplication

16p11.2 Microduplication Syndrome with Increased Fluid in the Cisterna: Coincidence or Phenotype Extension?

We report the first case of a child with 16p11.2 microduplication syndrome with increased fluid in the cisterna magna seen on magnetic resonance imaging (MRI). This finding may correspond to a Blake's Pouch Cyst (BPC) or a Mega Cisterna Magna (MCM), being impossible to differentiate through image examination. The molecular duplication was diagnosed using chromosomal microarray analysis with single nucleotide polymorphism (SNP). We review the clinical and neuroimaging features in published case reports in order to observe the findings described in the literature so far and present a skull three-dimensional model to contribute to a better understanding. Despite the variable expressivity of the syndrome being well known, there is no case described in the available literature that mentions the association of 16p11.2 microduplication and the presence of BPC or MCM seen in neuroimaging exams. This finding may represent an extension of the phenotype not yet reported or may present itself as a coincidence in a child with various malformations.

Case Report: Prenatal Whole-Exome Sequencing Identified a Novel Nonsense Mutation of the KCNH2 Gene in a Fetus With Familial 2q14.2 Duplication

Background: Pathogenic mutations in the KCNH2 gene were associated with long QT syndrome 2 (LQT2), which typically manifest in a prolonged QT interval and may lead to recurrent syncopes, seizure, or sudden death. Limited reports indicated that the KCNH2 mutations would result in LQT2 combined with tetralogy of fallot. Our goal was to present an additional case of LQT2 combined with the tetralogy of fallot in a fetus with a novel KCNH2 mutation.

Case presentation: Enrolled in this study was a 23-year-old pregnant woman from Quanzhou Fujian province, China. In her pregnancy, fetal ultrasound anomalies were identified, including tetralogy of fallot, coronary sinus enlargement, and persistent left superior vena cava. No chromosomal abnormality was detected by fetal karyotype analysis. However, 238.1-kb duplication in the 2q14.2 region containing the GLI2 gene was observed in the fetus by chromosomal array analysis, which was inherited from the mother with normal clinical features and interpreted as a variant of uncertain significance (VOUS). Furthermore, whole-exome sequencing (WES) detection identified a novel nonsense c.1907C > G (p.S636*) mutation in the KCNH2 gene in the fetus, and it was classified as a likely pathogenic variant, according to the ACMG guidelines. Parental verification analysis indicated that c.1907C > G (p.S636*) mutation was inherited from the mother.

Conclusion: In this study, we believe that 2q14.2 duplication may not be the reason for fetal heart defects; moreover, we described an additional case with KCNH2 gene mutation, which may lead to LQTS and be associated with congenital heart defects. In addition, our study further confirms the application value of the WES technology in prenatal genetic etiology diagnosis of fetuses with structural anomalies and unexplained structural variants.

A Novel VPS13B Mutation Identified by Whole-Exome Sequencing in Iranian Patients with Cohen Syndrome

Cohen syndrome is caused by homozygous mutation in the vacuolar protein sorting 13 homolog B (VPS13B, also referred to as COH1) gene on chromosome 8q22.2. The VPS13B protein is involved in transmembrane transport, Golgi integrity, and neuritogenesis. Clinical manifestations of Cohen syndrome are mainly intellectual disability, developmental delay, facial abnormalities, and eye disorders. This study aimed to identify the causative variant in two unrelated families with Cohen syndrome. To this end, whole-exome sequencing (WES) was performed to identify the pathogenic variants. A homozygous nonsense variant (NM_017890:c.10369C > T; NP_060360.3: p.Q3457X) in the VPS13B gene was identified and co-segregated with all affected individuals in both families. In silico analysis highly suggested this variant as damaging for protein function. The present study increases the mutation spectrum of the VPS13B gene and could be useful in genetic diagnosis and genetic counseling in Cohen syndrome patients.

A Novel Homozygous VPS13B Splice-Site Mutation Causing the Skipping of Exon 38 in a Chinese Family With Cohen Syndrome

Background: Cohen syndrome (CS) is a clinically heterogeneous disorder characterized by extensive phenotypic variation with autosomal recessive inheritance. VPS13B was identified to be the disease-causing gene for CS. The objectives of the present study were to screen likely pathogenic mutations of the patient with developmental delay and mental retardation, and to determinate the effect of this splice-site mutation by reverse transcription analysis. Methods: Whole exome sequencing (WES) in combination with Sanger sequencing were performed to identify the causative mutations of this CS family. Subsequently, the impact of the intronic variant on splicing was analyzed by reverse transcription and the construction of expression vector. Results: A novel homozygous splice-site mutation (c.6940+1G>T) in the VPS13B gene was identified in this proband. Sanger sequencing analysis of the cDNA demonstrated that the c.6940+1G>T variant could cause the skipping of entire exon 38, resulting in the loss of 208 nucleotides and further give rise to the generation of a premature in-frame stop codon at code 2,247. Conclusions: The homozygous VPS13B splicing variant c.6940+1G>T was co-segregated with the CS phenotypes in this family and was identified to be the cause of CS after comprehensive consideration of the clinical manifestations, genetic analysis and cDNA sequencing result.

Whole Exome Sequencing Identifies a Novel Homozygous Duplication Mutation in the VPS13B Gene in an Indian Family with Cohen Syndrome

Cohen syndrome (CS) is an autosomal recessive congenital disorder, characterized by hypotonia, intellectual disability, developmental delay, microcephaly, progressive retinopathy, neutropenia, truncal obesity, joint laxity, characteristic facial, ophthalmic, oral and appendage abnormalities, and an over friendly behavior. It has been linked to mutations in the VPS13B gene. The main purpose of this study was to determine the genetic cause of CS in an Indian family. Whole exome sequencing (WES) was used to identify the genetic cause of CS in the family. The WES analysis identified a homozygous novel duplication mutation c.5272dupG in the VPS13B gene, leading to formation of a truncating protein. The present study will be advantageous in genetic diagnosis and genetic counseling in CS, and increases the mutational spectrum of this gene.

CDG and immune response: From bedside to bench and back

Glycosylation is an essential biological process that adds structural and functional diversity to cells and molecules, participating in physiological processes such as immunity. The immune response is driven and modulated by protein-attached glycans that mediate cell-cell interactions, pathogen recognition and cell activation. Therefore, abnormal glycosylation can be associated with deranged immune responses. Within human diseases presenting immunological defects are congenital disorders of glycosylation (CDG), a family of around 130 rare and complex genetic diseases. In this review, we have identified 23 CDG with immunological involvement, characterized by an increased propensity to-often life-threatening-infection. Inflammatory and autoimmune complications were found in 7 CDG types. CDG natural history(ies) and the mechanisms behind the immunological anomalies are still poorly understood. However, in some cases, alterations in pathogen recognition and intracellular signaling (eg, TGF-β1, NFAT, and NF-κB) have been suggested. Targeted therapies to restore immune defects are only available for PGM3-CDG and SLC35C1-CDG. Fostering research on glycoimmunology may elucidate the involved pathophysiological mechanisms and open new therapeutic avenues, thus improving CDG patients' quality of life.

Exome sequencing identified a de novo mutation of PURA gene in a patient with familial Xp22.31 microduplication

The clinical significance of Xp22.31 microduplication is controversial as it is reported in subjects with developmental delay (DD), their unaffected relatives and unrelated controls. We performed multifaceted studies in a family of a boy with hypotonia, dysmorphic features and DD who carried a 600 Kb Xp22.31 microduplication (7515787-8123310bp, hg19) containing two genes, VCX and PNPLA4. The duplication was transmitted from his cognitively normal maternal grandfather. We found no evidence of the duplication causing the proband's DD and congenital anomalies based on unaltered expression of PNPLA4 in the proband and his mother in comparison to controls and preferential activation of the paternal chromosome X with Xp22.31 duplication in proband's mother. However, a de novo, previously reported deleterious, missense mutation in Pur-alpha gene (PURA) (5q31.2), with a role in neuronal differentiation was detected in the proband by exome sequencing. We propose that the variability in the phenotype in carriers of Xp22.31 microduplication can be due to a second and more deleterious genetic mutation in more severely affected carriers. Widespread use of whole genome next generation sequencing in families with Xp22.31 CNV could help identify such cases.

Gene analysis: A rare gene disease of intellectual deficiency-Cohen syndrome

Cohen syndrome is a rare, genetic, connective-tissue disorder, which is caused by mutations in the gene COH1 (VPS13B, Vacuolar Protein Sorting 13 Homolog B) at the chromosome 8q22. The disease is rare reported, which major clinical features include postnatal microcephaly, obesity, short stature, intellectual disability, progressive retinal dystrophy, intermittent neutropenia and many other unusual facial feature. We report four patients in China who were diagnosed with Cohen syndrome by genetic testing and clinical manifestations. At the same time, we review the related literature, and further expound the molecular mechanism of the disease, a variety of clinical manifestations, treatment and prognosis.

Practical approach to syndromic pediatric retinal dystrophies

PURPOSE OF REVIEW

The purpose of this review is to outline those systemic disorders that are associated with pediatric retinal dystrophy, summarize important retinal, and nonretinal clues that aid in syndromic diagnosis, provide an approach for ophthalmic and systematic systemic examination, describe the important systemic findings seen in pediatric syndromic retinal dystrophies and highlight the role of genetic testing.

RECENT FINDINGS

With profound advances being made in the field of molecular genetics, a definitive molecular etiology is increasingly being made even in rare and unusual forms of retinal dystrophies. Early recognition and precise diagnosis of a syndromic association has major clinical implications. It not only ensures early and holistic care to the child but also provides an opportunity for the parents in better understanding the nature and course of the disorder. It greatly aids in genetic counseling.

SUMMARY

Many syndromic retinal dystrophies may present initially to the ophthalmologist long before they present to the pediatrician with systemic symptoms. The intent of this article is to act as a resource in assisting the ophthalmologist to arrive at an early systemic diagnosis.