Exploring the pathological mechanisms underlying Cohen syndrome.

Cohen Syndrome (CS) is a rare autosomal recessive disorder caused by biallelic mutations in the VPS13B gene. It is characterized by multiple clinical features, including acquired microcephaly, developmental delay, intellectual disability, neutropenia, and retinal degeneration. VPS13B is part of the bridge-like lipid transport (BLTP) protein family, which in mammals also includes VPS13A, -C, and -D. The proteins of this family are peripheral membrane proteins with different sub-cellular localization, but all share similar structural features and have been proposed to act as lipid transport proteins at organellar membrane contact sites. VPS13B is localized at the Golgi apparatus and is essential for the maintenance of organelle architecture. Here we present a review of the experimental data on the function of the protein at the cellular level, discussing the potential link with disease phenotype and review the studies on animal models recapitulating features of the human disease.

Genetic landscape and clinical outcomes of autosomal recessive polycystic kidney disease in Kuwait.

Background: Autosomal recessive polycystic kidney disease (ARPKD), a rare genetic disorder characterized by kidney cysts, shows complex clinical and genetic heterogeneity. This study aimed to explore the genetic landscape of ARPKD in Kuwait and examine the intricate relationship between its genes and clinical presentation to enhance our understanding and contribute towards more efficient management strategies for ARPKD. Methods: This study recruited 60 individuals with suspected ARPKD from 44 different families in Kuwait. The participants were of different ethnicities and aged 0-70 years. Additionally, 33 were male, 15 were female, and 12 had indeterminant sex due to congenital anomalies. Comprehensive clinical data were collected. Mutations were identified by next-generation whole exome sequencing and confirmed using Sanger sequencing. Results: Of the 60 suspected ARPKD cases, 20 (33.3 %) died within hours of birth or by the end of the first month of life and one (1.7 %) within 12 months of birth. The remaining 39 (65.0 %) cases were alive, at the time of the study, and exhibited diverse clinical features related to ARPKD, including systematic hypertension (5.0 %), pulmonary hypoplasia (11.7 %), dysmorphic features (40.0 %), cardiac problems (8.3 %), cystic liver (5.0 %), Potter syndrome (13.3 %), developmental delay (8.3 %), and enlarged cystic kidneys (100 %). Twelve mutations, including novel truncating mutations, were identified in 31/60 cases (51.7 %) from 17/44 families (38.6 %). Additionally, 8/12 (66.7 %) mutations were in the PKHD1 gene, with the remaining four in different genes: NPHP3, VPS13P, CC2D2A, and ZNF423. Conclusions: This study highlights the spectrum of clinical features and genetic mutations of patients with ARPKD in Kuwait. It highlights the necessity for personalized approaches to improve ARPKD diagnosis and treatment, offering crucial insights into managing ARPKD.

Pseudohypoaldosteronism Type 1B and Cohen Syndrome: Novel Mutation, Unusual Combination, and Presentation.

Pseudohypoaldosteronism type 1 (PHA1) is a rare inherited disorder of resistance to aldosterone and presents with hyponatremia, hyperkalemia, and metabolic acidosis. Cohen syndrome (CS) is another rare inherited disease. Concurrent presentation with pseudohypoaldosteronism makes it so extraordinary and implies more challenges for clinicians. We report a case of a female with Cohen syndrome (novel mutation) and systemic pseudohypoaldosteronism, as well as the challenges we have encountered in the management of this patient.

Ultrastructural Abnormalities in Induced Pluripotent Stem Cell-Derived Neural Stem Cells and Neurons of Two Cohen Syndrome Patients.

Cohen syndrome is an autosomal recessive disorder caused by VPS13B (COH1) gene mutations. This syndrome is significantly underdiagnosed and is characterized by intellectual disability, microcephaly, autistic symptoms, hypotension, myopia, retinal dystrophy, neutropenia, and obesity. VPS13B regulates intracellular membrane transport and supports the Golgi apparatus structure, which is critical for neuron formation. We generated induced pluripotent stem cells from two patients with pronounced manifestations of Cohen syndrome and differentiated them into neural stem cells and neurons. Using transmission electron microscopy, we documented multiple new ultrastructural changes associated with Cohen syndrome in the neuronal cells. We discovered considerable disturbances in the structure of some organelles: Golgi apparatus fragmentation and swelling, endoplasmic reticulum structural reorganization, mitochondrial defects, and the accumulation of large autophagosomes with undigested contents. These abnormalities underline the ultrastructural similarity of Cohen syndrome to many neurodegenerative diseases. The cell models that we developed based on patient-specific induced pluripotent stem cells can serve to uncover not only neurodegenerative processes, but the causes of intellectual disability in general.

A Possible Role of VPS13B in the Formation of Golgi-Lipid Droplet Contacts Associating with the ER.

While the physical interactions between the Golgi apparatus (Golgi) and lipid droplets (LDs) have been suggested through system-level imaging, the Golgi-LD membrane contact sites (MCSs) remain largely uncharacterized. Here, we show evidence to support the existence of Golgi-LD MCSs in HEK293 cells. We further suggest that vacuolar protein sorting-associated protein 13B (VPS13B) localizes to and promotes the formation of Golgi-LD contacts upon oleic acid (OA) stimulation using 3D high-resolution microscopy. Depletion of VPS13B moderately affects the formation of Golgi-LD contacts upon OA treatment in addition to the fragmentation of the Golgi. Although cellular functions of VPS13B-mediated contacts are still elusive, these findings may provide a new insight into related diseases caused by loss-of-function mutations of VPS13B.

Deletion as novel variants in VPS13B gene in Cohen syndrome: Case series.

Background: Cohen syndrome (OMIM No. # 216550) is a rare autosomal recessive disorder caused by homozygous mutation in the vacuolar protein sorting 13 homolog B (VPS13B) gene on chromosome 8q22.2. Clinical manifestations include hypermobile joints, microcephaly, intellectual disabilities, craniofacial and limb anomalies, and neutropenia. To date, more than 200 mutations of VPS13B have been reported in over 1,000 Cohen syndrome patients. This article reviews the clinical data of two cases of Cohen syndrome diagnosed by whole exome sequencing. Results: Both children visited for psychomotor retardation. Gene detection showed a mutation in 8q22.2, NM_017890.4 Intron38 c.6940+1G > T and heterozygotic deletion of exon 3-19 of the VPS13B gene (Case 1), and a mutation in 8q22.2, NM_017890.4 Intron38 c.6940+1G > T and 8q22, NM_017890.4 Exon56 c10334_10335del in the VPS13B gene (Case 2). The variation was predicted to be pathogenic by related software, and they have not been reported. Conclusion: Cohen syndrome should be considered in the differential diagnosis of any child with developmental retardation and neutropenia. The present study increases the mutation spectrum of the VPS13B gene and could be helpful in genetic diagnosis and genetic counseling in Cohen syndrome patients.

Characterization of Vps13b-mutant mice reveals neuroanatomical and behavioral phenotypes with females less affected.

The vacuolar protein sorting-associated protein 13B (VPS13B) is a large and highly conserved protein. Disruption of VPS13B causes the autosomal recessive Cohen syndrome, a rare disorder characterized by microcephaly and intellectual disability among other features, including developmental delay, hypotonia, and friendly-personality. However, the underlying mechanisms by which VPS13B disruption leads to brain dysfunction still remain unexplained. To gain insights into the neuropathogenesis of Cohen syndrome, we systematically characterized brain changes in Vps13b-mutant mice and compared murine findings to 235 previously published and 17 new patients diagnosed with VPS13B-related Cohen syndrome. We showed that Vps13b is differentially expressed across brain regions with the highest expression in the cerebellum, the hippocampus and the cortex with postnatal peak. Half of the Vps13b-/- mice die during the first week of life. The remaining mice have a normal lifespan and display the core phenotypes of the human disease, including microcephaly, growth delay, hypotonia, altered memory, and enhanced sociability. Systematic 2D and 3D brain histo-morphological analyses reveal specific structural changes in the brain starting after birth. The dentate gyrus is the brain region with the most prominent reduction in size, while the motor cortex is specifically thinner in layer VI. The fornix, the fasciculus retroflexus, and the cingulate cortex remain unaffected. Interestingly, these neuroanatomical changes implicate an increase of neuronal death during infantile stages with no progression in adulthood suggesting that VPS13B promotes neuronal survival early in life. Importantly, whilst both sexes were affected, some neuroanatomical and behavioral phenotypes were less pronounced or even absent in females. We evaluate sex differences in Cohen patients and conclude that females are less affected both in mice and patients. Our findings provide new insights about the neurobiology of VPS13B and highlight previously unreported brain phenotypes while defining Cohen syndrome as a likely new entity of non-progressive infantile neurodegeneration.

Clinical characterization of patients with schizophrenia and 16p13.11 duplication: A case series.

BACKGROUND: Chromosome 16p13.11 duplication is a well-known genetic risk factor for schizophrenia (SCZ) (odds ratio = 1.84). However, no case reports focusing on patients with SCZ and 16p13.11 duplication have been published. Therefore, here, we report the detailed clinical cases of four patients with SCZ and 16p13.11 duplication who were identified in our previous whole-genome copy number variant (CNV) study. CASE PRESENTATION: In the four patients with SCZ and 16p13.11 duplication detected by array comparative genomic hybridization, one patient was found to have treatment-resistant SCZ and an additional pathogenic rare CNV. Two of the four patients in this study had environmental risk factors that may have been involved in the development of SCZ. CONCLUSIONS: The results of this case series suggest that a genetic cohort study would be useful for evaluating which genetic and environmental risk factors could better explain the variable expressivity of 16p13.11 duplication. Furthermore, this work could be useful for elucidating the pathophysiology of SCZ.

Cohen syndrome and early-onset epileptic encephalopathy in male triplets: two disease-causing mutations in VPS13B and NAPB.

Cohen syndrome (CS) is a rare multisystem autosomal recessive disorder associated with mutations in VPS13B (vacuolar protein sorting homolog 13B). The NAPB-related neurodevelopmental disorder is characterized mainly by early-onset epileptic encephalopathy (EOEE) and is associated with mutations in NAPB that encodes for SNAP-beta (soluble NSF attachment protein beta). Here we describe male triplets, clinically presenting with the phenotype of subtle but distinctive facial features, intellectual disability, increased body weight, neonatal EOEE, and prominently variable abnormal behaviors of autism and sexual arousal. The EEG showed multifocal epilepsy, while the brain MRI showed no abnormalities. Diagnostic exome sequencing (ES), the applied next-generation sequencing approach, revealed the interesting finding of two novel homozygous variants in two genes: VPS13B missense variant (c.8516G > A) and NAPB splice-site loss (c.354 + 2 T > G). Sanger sequencing verified the segregation of the two recessive gene variants with the phenotype in family members. The prediction algorithms support the pathogenicity of these variants. Homozygosity mapping of ES data of this consanguineous family revealed multiple chromosomal regions of homozygosity stretches with the residing of VPS13B (chr8: 100830758G > A) and NAPB (Chr20: 23,375,774 A > C) variants within the largest homozygous blocks further supporting the disease-genes causal role. Interestingly, the functions of the two proteins; VPS13B, a transmembrane protein involved in intracellular protein transport, and SNAP-beta involved in neurotransmitters release at the neuronal synaptic complexes, have been associated with Golgi-mediated vesicular trafficking. Our ES findings provide new insights into the pathologic mechanism underlying the expansion of the neurodevelopmental spectrum in CS and further highlight the importance of Golgi and Golgi-membrane-related proteins in the development of neurodevelopmental syndromes associated with early-onset non-channelopathy epilepsy. To our knowledge, this is the first report documenting multifocal EOEE in CS patients with the association of a pathogenic NAPB variant.

Early Diagnostic Signs and the Natural History of Typical Findings in Cohen Syndrome.

OBJECTIVE: To describe the clinical presentation and long-term clinical features of a molecularly confirmed cohort with Cohen syndrome. STUDY DESIGN: Twelve patients with Cohen syndrome aged 0.2-13.9 years from 8 families with a median follow-up of 7 years were enrolled to the study. Genetic analyses were made by VPS13B and whole-exome sequencing analyses. RESULTS: Biallelic VPS13B variants, including 3 nonsense, 1 frameshift, and 1 splice-site variant, and a multiexon deletion were detected. Prader-Willi syndrome-like features such as hypotonia, small hands, round face with full cheeks, almond-shaped eyes, and micrognathia were observed in all infantile patients. Beginning from age 4 years, it was noticed that the face gradually elongated and became oval. The typical facial features of Cohen syndrome such as a long face, beak-shaped nose, and open-mouth appearance with prominent upper central incisors became evident at age 9. Other Cohen syndrome features including retinopathy (11/11), neutropenia (11/12), truncal obesity (5/12), and myopia (5/11) were detected at the median ages of 7.8, 7, 7.5, and 5 years, respectively. Eleven patients aged older than 5 years at their last examination had severe speech delay. CONCLUSIONS: A differential diagnosis of Cohen syndrome in the infancy should be made with Prader-Willi syndrome, and that the typical facial features for Cohen syndrome is prominent at age 9 years, when retinopathy, neutropenia, and truncal obesity become evident. Moreover, adding the severe speech delay to the diagnostic criteria should be considered.

VPS13B gene variation and clinical phenotype of Cohen syndrome in a Chinese Han family / 中华实验眼科杂志

Objective:To analyze the pathogenicity and clinical characteristics of patients with Cohen syndrome caused by a compound heterozygous variation of VPS13B gene. Methods:A pedigree investigation was conducted.A Chinese Han family with Cohen syndrome was recruited from Henan Eye Hospital in September 2021.There were three members of two generations in this family, including one patient.The clinical data of the proband and his parents were collected, and the relevant ophthalmic and general examinations were performed to evaluate the clinical phenotype.The peripheral venous blood samples of the family members were collected to extract whole genomic DNA, and the whole exome sequencing was performed.Sanger sequencing and pedigree co-segregation analysis were performed among the family members.According to the ACMG guidelines, the pathogenicity of the selected variants was evaluated and the online tools were used to predict the pathogenicity of the variants.Relevant literature of Cohen syndrome were retrieved in Online Mendelian Inheritance in Man (OMIM) and PubMed, China National Knowledge Infrastructure and Wanfang databases by taking Cohen syndrome and VPS13B gene as the searching keywords.The clinical manifestations and pathogenic variants of patients in the literature were summarized, and the relationship between genotype and clinical phenotype was analyzed.This study protocol adhered to the Declaration of Helsinki and was approved by the Ethics Committee of Henan Eye Hospital (No.HNEECKY-2019[15]). Both the subject and the patient's guardian were aware of the study purpose and method.Written informed consent was obtained. Results:The family was consistent with autosomal recessive inheritance.The proband, a 5-year-old male, had bilateral night blindness with photophobia, ptosis, lower eyelid entropion, and trichiasis; high myopia in both eyes; osteoblastoid pigmentation in the peripheral retina, atrophy and thinning of the outer layer of the peripheral retina, extinguished flashing electroretinogram; global growth retardation, typical facial features, slender fingers and toes, flatfoot, foot valgus, dystonia, no cardiac abnormalities; excessively cheerful personality.The clinical manifestations of the proband were consistent with Cohen syndrome.No obvious abnormality was found in the clinical phenotype and the auxiliary examination of the proband's parents.Whole exon sequencing revealed that the proband carried two heterozygous variations, a nonsense variation c. 11713C>T(p.Gln3905*) and a splicing variation c. 6940+ 1G>T.Sanger sequencing confirmed that the above variations were co-segregated in this family.c.11713C>T(p.Gln3905*) was a novel variant, which prematurely terminated the protein encoded by it and affected the normal function of the protein.The two variations were pathogenic variants according to the ACMG guidelines.A total of 12 articles on variants and clinical characteristics of Cohen syndrome in China were retrieved.Combined with the results of this study, a total of 24 VPS13B variants were found in Chinese patients, of which the incidence of frameshift variation was 41.7%(10/24), missense variation 20.8%(5/24), splicing variation 20.8%(5/24) and nonsense variation 16.7%(4/24), respectively.The onset age of patients with Cohen syndrome was from 28 days to 12 years old.The symptoms such as nerve system, eye, brain, and bone were sporadic, and the clinical manifestations were highly heterogeneous. Conclusions:A novel pathogenic variation c. 11713C>T is found in the VPS13B gene of the Cohen syndrome pedigree in this study, and expands the pathogenic variation spectrum of the VPS13B gene.The clinical manifestations of Cohen syndrome are highly heterogeneous.

Multiorgan neutrophilic inflammation in a Border Collie with "trapped" neutrophil syndrome.

Trapped neutrophil syndrome is a rare congenital disease recognized in Border Collies and is characterized by persistent neutropenia with myeloid hyperplasia. The mechanism of neutropenia has not been described. We document the case of a young Border Collie diagnosed with trapped neutrophil syndrome based on clinical features, blood and bone marrow evaluation, and presence of the associated homozygous mutation. Results from flow cytometric and storage studies suggested lower neutrophil survival time. The dog had substantial neutrophilic inflammation in multiple organs, indicating that neutrophils could leave the marrow and enter tissues, making the term "trapped" neutrophil syndrome a misnomer.

Cohen syndrome in two patients from China.

BACKGROUND: Cohen syndrome (CS; OMIM 216550) is a rare syndrome with evident clinical heterogeneity. The diverse phenotype comprises early-onset hypotonia and developmental delays, intellectual disabilities, microcephaly, hypermobile joints, neutropenia, myopia, and characteristic facial features. The disease is rarely reported. Vacuolar Protein Sorting 13 Homolog B (VPS13B; OMIM 607817) is the only causative gene of CS. METHODS: Blood samples sourced from both siblings and parents were sent to identify mutations by trio-WES, and changes in the patient's condition were understood through consultation data and follow-up. RESULTS: We reported two siblings affected by developmental delay, microcephaly, intellectual disability, and facial features. The siblings' WES detected compound heterozygous variants in the exon region of VPS13B (NM_017890): c.9337A>T and c.8551A>C. CONCLUSION: Two individuals were diagnosed with CS by genetic testing and clinical features. In addition, we conduct a brief review of the reports on the Chinese population with CS and reinforce the understanding of the correlation between genotype-phenotype.

Síndrome de Cohen: reporte de caso y revisión de la literatura / Cohen syndrome: case report and literature review

Resumen Introducción: el Síndrome de Cohen es una enfermedad genética monogénica autosómica recesiva, que se origina a partir de mutaciones en el gen VPS13B (COH1). Se caracteriza por obesidad, retraso psicomotor, microcefalia, hipotonía, miopía progresiva, distrofia retiniana, neutropenia intermitente y rasgos faciales particulares. Objetivo: presentar el segundo caso reportado en Colombia, que fue confirmado mediante estudio molecular. También se presenta una breve revisión de la literatura médica más reciente sobre esta patología. Caso clínico: adolescente de 14 años con microcefalia, trastorno cognitivo, malformaciones menores asociadas, neutropenia y obesidad, con mutación homocigota del gen VPS13B. Conclusión: a pesar de ser un síndrome poco común, con importante variabilidad fenotípica, debe sospecharse con base en los criterios clínicos y en las patologías asociadas.

Abstract Introduction: cohen's syndrome is an autosomal recessive monogenic genetic disease, which originates from mutations in the VPS13B (COH1) gene. It is characterized by obesity, psychomotor retardation, microcephaly, hypotonia, progressive myopia, retinal dystrophy, intermittent neutropenia, and classic facial features. Objective: to present the second case reported in Colombia, which was confirmed by molecular study. A brief review of the most recent medical literature on this pathology is also presented. Clinical case: a 14-year-old adolescent with microcephaly, cognitive disorder, minor associated malformations, neutropenia, and obesity, with a homozygous VPS13B gene mutation. Conclusion: despite being a rare syndrome, with significant phenotypic variability, it should be suspected based on clinical criteria and associated pathologies.

A partnership between the lipid scramblase XK and the lipid transfer protein VPS13A at the plasma membrane.

Chorea-acanthocytosis (ChAc) and McLeod syndrome are diseases with shared clinical manifestations caused by mutations in VPS13A and XK, respectively. Key features of these conditions are the degeneration of caudate neurons and the presence of abnormally shaped erythrocytes. XK belongs to a family of plasma membrane (PM) lipid scramblases whose action results in exposure of PtdSer at the cell surface. VPS13A is an endoplasmic reticulum (ER)-anchored lipid transfer protein with a putative role in the transport of lipids at contacts of the ER with other membranes. Recently VPS13A and XK were reported to interact by still unknown mechanisms. So far, however, there is no evidence for a colocalization of the two proteins at contacts of the ER with the PM, where XK resides, as VPS13A was shown to be localized at contacts between the ER and either mitochondria or lipid droplets. Here we show that VPS13A can also localize at ER-PM contacts via the binding of its PH domain to a cytosolic loop of XK, that such interaction is regulated by an intramolecular interaction within XK, and that both VPS13A and XK are highly expressed in the caudate neurons. Binding of the PH domain of VPS13A to XK is competitive with its binding to intracellular membranes that mediate other tethering functions of VPS13A. Our findings support a model according to which VPS13A-dependent lipid transfer between the ER and the PM is coupled to lipid scrambling within the PM. They raise the possibility that defective cell surface exposure of PtdSer may be responsible for neurodegeneration.

A rare canonical splice-site variant in VPS13B causes attenuated Cohen syndrome.

BACKGROUND: To describe a patient with a history of obesity, retinal dystrophy, type II diabetes, and mild cognitive impairment; found to harbour biallelic splice-site variants in VPS13B. MATERIALS & METHODS: A complete ophthalmic evaluation was performed at Moorfields Eye Hospital (London, United Kingdom), consisting of measurement of best-corrected visual acuity (BCVA), slit lamp and dilated fundus evaluation, colour, autofluorescence and near-infrared retinal imaging, spectral domain-optical coherence tomography, and electroretinogram (ERG). Whole-genome sequencing was performed as part of the UK's 100,000 Genomes Project. RESULTS: A 26-year-old Pakistani man with normal appearance, stature, and head size presented with decreased BCVA and severely constricted visual fields to our Ophthalmic Genetics clinic. He had a history of obesity, type II diabetes, and mild cognitive impairment. His evaluation showed retina-wide, severe photoreceptor dysfunction in both eyes, with undetectable scotopic and photopic ERG waveforms. Genomic analysis identified a homozygous rare splice donor variant in the VPS13B gene (c.5024+2T>C) that was demonstrated to lead to skipping of the in-frame exon 31 (p.Gln1607_Ser1675delinsHis). CONCLUSIONS: Exon 31 skipping in VPS13B may lead to a hypomorphic change, with partial gene function and an incomplete, mild Cohen syndrome-like phenotype.

Identification of a Novel VPS13B Mutation in a Chinese Patient with Cohen Syndrome by Whole-Exome Sequencing.

OBJECTIVE: The present study aims to investigate the clinical features and diagnostic characteristics of children with Cohen syndrome caused by the vacuolar protein sorting 13 homolog B (VPS13B) gene mutation and to review the relevant literature to provide a reference for genetic counseling and the diagnosis of Cohen syndrome. METHODS: The clinical data and molecular genetic test results of a child with Cohen syndrome were retrospectively analyzed and a review of the relevant literature was conducted. RESULTS: A two-year-and-four-month-old boy was referred to the hospital for recurrent fever and shortness of breath. On physical examination, the boy was found to have growth retardation, thick bushy hair, microcephaly, hypertelorism, down-slanting palpebral fissures, and hypotonia. Genetic testing was performed, and the results suggested the presence of exon 20-32 heterozygous deletion and c.8275 delC (p.R2759 fs*18) heterozygous variant on the VPS13B gene from phenotypically normal parents. These two mutation loci have not been reported in the literature, and they were predicted by relevant software to be pathogenic variants. CONCLUSION: We identified two novel variants in the VPS13B gene (exon 20-32 heterozygous deletion and c.8275 delC heterozygous variant) in a boy with Cohen syndrome, thus extending the spectrum of VPS13B gene variants in patients with Cohen syndrome.

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.