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.

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.

Spatial Learning and Motor Deficits in Vacuolar Protein Sorting-associated Protein 13b (Vps13b) Mutant Mouse

Vacuolar protein sorting-associated protein 13B (VPS13B), also known as COH1, is one of the VPS13 family members which is involved in transmembrane transport, Golgi integrity, and neuritogenesis. Mutations in the VPS13B gene are associated with Cohen syndrome and other cognitive disorders such as intellectual disabilities and autism spectrum disorder (ASD). However, the patho-physiology of VPS13B-associated cognitive deficits is unclear, in part, due to the lack of animal models. Here, we generated a Vps13b exon 2 deletion mutant mouse and analyzed the behavioral phenotypes. We found that Vps13b mutant mice showed reduced activity in open field test and significantly shorter latency to fall in the rotarod test, suggesting that the mutants have motor deficits. In addition, we found that Vps13b mutant mice showed deficits in spatial learning in the hidden platform version of the Morris water maze. The Vps13b mutant mice were normal in other behaviors such as anxiety-like behaviors, working memory and social behaviors. Our results suggest that Vps13b mutant mice may recapitulate key clinical symptoms in Cohen syndrome such as intellectual disability and hypotonia. Vps13b mutant mice may serve as a useful model to investigate the pathophysiology of VPS13B-associated disorders.

Ophthalmologic Findings in Cohen Syndrome

PURPOSE: We report two cases of Cohen syndrome associated with ophthalmologic findings, which is the first such report from Korea. METHODS: A 14-year-old boy and a 13-year-old girl, a brother and sister, who had visited the department of pediatrics for evaluation of developmental disorders was transferred to the department of ophthalmology due to evidence of nyctalopia and decreased visual acuity. There, refraction, ultrasonography, and fundus examinations were performed. RESULTS: The children had high myopia, and refractive astigmatism. Bull's eye maculopathy with a pale disc was found on the fundus examination. There were characteristic facial appearances including wave-shaped, down-slanting palpebral fissures and short philtrum. They also had grimacing expressions upon smiling. Neutropenia was identified in the female patient. CONCLUSIONS: Cohen syndrome should be suspected and considered in the differential diagnosis of patients with high myopia, nyctalopia, and decreased visual acuity.