Cohen syndrome: report of nine cases and review of the literature, with emphasis on ophthalmic features

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.

Mapping the Diverse Genetic Disorders and Rare Diseases Among the Syrian Population: Implications on Refugee Health and Health Services in Host Countries

The aim of this systematic review is to provide physicians and researchers with a comprehensive list of reported genetic disorders in patients of Syrian origin-those who have become part of the largest displaced population globally-and to highlight the need to consider migrant population-based risk for the development of genetic disease control and prevention programs. This review was performed based on the 2015 PRISMA and the international prospective register of systematic reviews. The present review reports on a total of 166 genetic disorders (only 128 reported on OMIM) identified in the Syrian population. Of these disorders, 27% are endocrine-, nutritional- and metabolic-related diseases. Second to metabolic disorders are congenital malformations, deformations and chromosomal abnormalities. Diseases of the blood and the blood-forming organs accounted for 13% of the total genetic disorders. The majority of the genetic disorders reported in Syrian patients followed an autosomal recessive mode of inheritance. These findings are a reflection of the high rates of consanguineous marriages that favor the increase in incidence of these diseases. From the diseases that followed an autosomal recessive mode of inheritance, 22% are reported to be only present in Syria and other regional countries. Twelve of these genetic diseases were identified to be strictly diagnosed in individuals of Syrian origin. The present systematic review highlights the need to develop programs that target genetic disorders affecting Syrian migrants in host countries. These programs would have potential financial and economic benefits, as well as a positive impact on the physical and mental health of members of the Syrian refugee community and those of their host societies. In turn, this would decrease the burden on the health systems in host countries.

Cystoid maculopathy is a frequent feature of Cohen syndrome-associated retinopathy

Cohen syndrome (CS) is a rare syndromic form of rod-cone dystrophy. Recent case reports have suggested that cystoid maculopathy (CM) could affect CS patients with an early onset and high prevalence. Our study aims at improving our understanding and management of CM in CS patients through a retrospective case series of ten CS patients with identified pathogenic variants in VPS13B. Longitudinal optical coherence tomography (OCT) imaging was performed and treatment with carbonic anhydrase inhibitors (CAI) was provided to reduce the volume of cystoid spaces. CM affected eight out of ten patients in our cohort. The youngest patient showed a strong progression of macular cysts from the age of 4.5 to 5 years despite oral CAI medication. Other teenage and young adult patients showed stable macular cysts with and without treatment. One patient showed a moderate decrease of cystoid spaces in the absence of treatment at 22 years of age. Through a correlative analysis we found that the volume of cystoid spaces was positively correlated to the thickness of peripheral and macular photoreceptor-related layers. This study suggests that CAI treatments may not suffice to improve CM in CS patients, and that CM may resolve spontaneously during adulthood as photoreceptor dystrophy progresses.

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.

Cohen Syndrome-Associated Cataract Is Explained by VPS13B Functions in Lens Homeostasis and Is Modified by Additional Genetic Factors

Purpose

Cohen syndrome (CS) is a rare genetic disorder caused by variants of the VPS13B gene. CS patients are affected with a severe form of retinal dystrophy, and in several cases cataracts also develop. The purpose of this study was to investigate the mechanisms and risk factors for cataract in CS, as well as to report on cataract surgeries in CS patients.

Methods

To understand how VPS13B is associated with visual impairments in CS, we generated the Vps13b^{∆Ex3/∆Ex3} mouse model. Mice from 1 to 3 months of age were followed by ophthalmoscopy and slit-lamp examinations. Phenotypes were investigated by histology, immunohistochemistry, and western blot. Literature analysis was performed to determine specific characteristic features of cataract in CS and to identify potential genotype–phenotype correlations.

Results

Cataracts rapidly developed in 2-month-old knockout mice and were present in almost all lenses at 3 months. Eye fundi appeared normal until cataract development. Lens immunostaining revealed that cataract formation was associated with the appearance of large vacuoles in the cortical area, epithelial–mesenchymal transition, and fibrosis. In later stages, cataracts became hypermature, leading to profound retinal remodeling due to inflammatory events. Literature analysis showed that CS-related cataracts display specific features compared to other forms of retinitis pigmentosa-related cataracts, and their onset is modified by additional genetic factors. Corroboratively, we were able to isolate a subline of the Vps13b^{∆Ex3/∆Ex3} model with delayed cataract onset.

Conclusions

VPS13B participates in lens homeostasis, and the CS-related cataract development dynamic is linked to additional genetic factors.

Coexistence of bilateral macular edema and pale optic disc in the patient with Cohen syndrome

Background

Cohen syndrome (Q87.8;ORPHA:193; OMIM#216550) is an autosomal recessive inherited genetic disorder caused by mutation in the VPS13B/COH1 gene. It is characterized by variable clinical symptoms such as deformity of the head, face, hands and feet, eye abnormalities, abdominal obesity, neutropenia and nonprogressive intellectual disability. The typical lesions in the eyeball in Cohen syndrome include high myopia, retinal dystrophy, strabismus, maculopathy and lens subluxation. The present study describes the coexistence of bilateral macular edema with pale optic disc in a patient with a homozygous deletion in the VPS13B/COH1 gene.

Material and methods

A 6-year-old Caucasian girl with facial dysmorphism, microcephaly, prominent upper incisors, narrow hands with slender fingers, congenital heart defect and ophthalmic symptoms was subjected to genetic testing. The genetic evaluation revealed a homozygous deletion on the long arm of chromosome 8 encompassing 20-25 exons of the VPS13 gene, as confirmed by Cohen syndrome. She underwent a full ophthalmological examination with the assessment of slit lamp examination of anterior segment and fundoscopy, refraction error, biometry, central corneal thickness and additionally electroretinography, optical coherence tomography and fundus photography.

Results

In the ophthalmologic examination, the girl had bilateral astigmatism accompanied by myopia and a marked reduction in central corneal thickness. Fundus examination showed pale optic nerve discs and "salt and pepper" retinopathy. Bilateral cystic macular edema was revealed in handheld optical coherence tomography. Electroretinography showed a reduced response amplitude of cones and rods.

Conclusion

In a patient with high myopia, macular edema, pale optic disc and facial dysmorphism, Cohen syndrome should be considered in the differential diagnosis. The severity of individual clinical features in patients with Cohen syndrome varies. It can be assumed that the type of mutation affects the occurrence and severity of individual symptoms.

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.

Ophthalmic features of retinitis pigmentosa in Cohen syndrome caused by pathogenic variants in the VPS13B gene

PURPOSE

The aim of this study is to report on the phenotype and genotype of five patients diagnosed with Cohen syndrome, an extremely rare autosomal recessive disorder manifesting with mental and physiological defects.

METHODS

Five patients from three German families and one Syrian family underwent a comprehensive ophthalmological examination. The scheduled visual acuity measurements, fundus ophthalmoscopy, spectral domain optical coherence tomography (OCT), full-field electrophysiological recordings of scotopic and photopic electroretinograms (ERGs) and colour vision testing could not be carried out in all subjects, because of the mental and physical retardation. The genetic diagnosis was achieved by next-generation sequencing.

RESULTS

The ophthalmic and systemic phenotype of the patients is typical for Cohen syndrome including myopia, night blindness, photophobia, fundus pigmentary changes and bull's eye maculopathy. Electroretinograms (ERGs) were extinguished in the four patients, whose recording was possible. Genetic testing revealed homozygous or two heterozygous bi-allelic mutations in the VPS13B (COH1) gene in all five patients, with five different allelic variants observed. The homozygous mutation c.6055_6056delGA; p.Asp2019Glnfs*15 in two sibling patients as well as the homozygous nonsense mutation c.8112C>G;p.Tyr2704* have not previously been reported.

CONCLUSIONS

The phenotype of the five patients reported here is typical for Cohen syndrome; however, their genotype is heterogeneous. Two new allelic variants were found to be the causative mutation.

Cohen Syndrome: Review of the Literature

Cohen syndrome was initially described as a syndrome including obesity, hypotonia, mental deficiency, and facial, oral, ocular and limb anomalies. Leukopenia, especially neutropenia, was later described as a feature of Cohen syndrome. Cohen syndrome is caused by an autosomal recessive (AR) mutation of the vacuolar protein sorting 13 homolog B (VPS13B, also referred to as COH1) gene on chromosome 8q22.2.

[Psychomotor retardation with neutropenia for more than one year in a toddler]

A boy was admitted at the age of 17 months. He had psychomotor retardation in early infancy. Physical examination revealed microcephalus, unusual facies, and a single palmar crease on his right hand, as well as muscle hypotonia in the extremities and hyperextension of the bilateral shoulder and hip joints. Genetic detection identified two pathogenic compound heterozygous mutations, c.8868-1G>A (splicing) and c.11624_11625del (p.V3875Afs*10), in the VPS13B gene, and thus the boy was diagnosed with Cohen syndrome. Cohen syndrome is a rare autosomal recessive disorder caused by the VPS13B gene mutations and has complex clinical manifestations. Its clinical features include microcephalus, unusual facies, neutropenia, and joint hyperextension. VPS13B gene detection helps to make a confirmed diagnosis.

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.

A canine model of Cohen syndrome: Trapped Neutrophil Syndrome

BACKGROUND

Trapped Neutrophil Syndrome (TNS) is a common autosomal recessive neutropenia in Border collie dogs.

RESULTS

We used a candidate gene approach and linkage analysis to show that the causative gene for TNS is VPS13B. We chose VPS13B as a candidate because of similarities in clinical signs between TNS and Cohen syndrome, in human, such as neutropenia and a typical facial dysmorphism. Linkage analysis using microsatellites close to VPS13B showed positive linkage of the region to TNS. We sequenced each of the 63 exons of VPS13B in affected and control dogs and found that the causative mutation in Border collies is a 4 bp deletion in exon 19 of the largest transcript that results in premature truncation of the protein. Cohen syndrome patients present with mental retardation in 99% of cases, but learning disabilities featured in less than half of TNS affected dogs. It has been implied that loss of the alternate transcript of VPS13B in the human brain utilising an alternate exon, 28, may cause mental retardation. Mice cannot be used to test this hypothesis as they do not express the alternate exon. We show that dogs do express alternate transcripts in the brain utilising an alternate exon homologous to human exon 28.

CONCLUSION

Dogs can be used as a model organism to explore the function of the alternately spliced transcript of VPS13B in the brain. TNS in Border collies is the first animal model for Cohen syndrome and can be used to study the disease aetiology.

Ophthalmic findings in the Greek isolate of Cohen syndrome

A high frequency of the Cohen syndrome has been observed in a Greek island with 2,000 inhabitants and a high degree of inbreeding. All patients were homozygous for a COH1, exon 6-16 deletion suggesting a founder effect. We present the results of their first systematic ophthalmologic assessment. Myopia and chorioretinal atrophy were present in all patients of this cohort. Yet, in contrast to all groups previously reported, the majority presented with corneal changes, independently from age, gender, and family history. A pair of sisters, aged 11 and 15 years old, presented with bilateral keratoconus. More frequently (86%) than in any other ethnic group, Greek patients had cataracts that were bilateral and often graded as high as 3, even at a young age. As a whole, the ophthalmic phenotype of the Greek isolate of Cohen syndrome is characterized by the involvement of both the posterior and the anterior eye segment, bilaterally, in the majority of cases (93%). Greek Cohen patients that share a founder mutation are at a higher risk of developing blindness in respect to those of other ethnicities and genotypes. This study highlighted the need for pachymetry measurement as a means of surveillance and prediction of the visual impairment frequently observed.

Mutations of a country: a mutation review of single gene disorders in the United Arab Emirates (UAE)

The United Arab Emirates inhabitants are ethnically diverse, with ancestries from Arabia, Persia, Baluchistan, and Africa. However, the majority of the current five million inhabitants are expatriates from the Asian subcontinent, Middle Eastern, African, and European countries. Consanguineous marriages within most UAE subpopulations are still the norm, leading to the formation of isolates and higher frequencies of recessive conditions. The UAE is ranked sixth in terms of prevalence of birth defects, with more than 270 genetic disorders reported in the national population. The UAE has high frequencies of blood disorders including thalassemias, sickle cell disease, and G6PD. In addition, certain genetic conditions are relatively common including cystic fibrosis, Joubert, and Meckel syndromes. Furthermore, numerous rare congenital malformations and metabolic disorders have been reported. We review the single gene disorders that have been studied at the molecular level in the UAE (which currently stand at 76) and compile the mutations found. Several novel (p.S2439fs) mutations have been reported including c.7317delA in NF1, c.5C>T (p.A2V) in DKC1, c.1766T>A (p.I589N) in TP63, and c.2117G>T (p.R706L) in VLDLR. We hope that this review will form the basis to establish a UAE mutations database and serve as a model for the collection of mutations of a country.

Astigmatism in preschool children in Taiwan

PURPOSE

To elucidate the prevalence of astigmatism and its corneal component, the association between the amount of astigmatism and its axis, and the association between the axis of astigmatism and body mass index (BMI) in Taiwanese preschool children.

METHODS

In this population-based study we analyzed 2 data sets, one obtained by retrospective review of vision-screening data and another obtained in a prospective observational study. Each study collected data for age, sex, and refraction status. Autokeratometry, height, and weight measurements were obtained only in the observational study. Astigmatism was classified as with-the-rule, against-the-rule, or oblique.

RESULTS

The prevalence of astigmatism was unassociated with age or sex in both data sets. The retrospective study (1,094 subjects; mean age, 5 years; range, 2.19-7.32 years) revealed that 13.3% of the subjects had astigmatism > or = 1.00 D, and most of them had with-the-rule astigmatism; 4.0% had high astigmatism (>1.50 D). Children with with-the-rule astigmatism had greater mean cylinder power than those with against-the-rule or oblique astigmatism. In the prospective study (190 subjects; mean age, 5.65 years; range, 3.79-6.68 years) astigmatism correlated with its corneal component. Preschoolers with with-the-rule astigmatism and with-the-rule corneal astigmatism had greater BMI and heavier weight than those with against-the-rule or oblique type.

CONCLUSIONS

Astigmatism is common in Taiwanese preschool children. The predominant types are with-the-rule and oblique astigmatism. Most patients with high astigmatism and high corneal astigmatism have with-the-rule type. High BMI or weight is associated with with-the-rule astigmatism and with with-the-rule corneal astigmatism.