Genetic and clinical heterogeneity of Moyamoya disease
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BACKGROUND: Moyamoya disease (MMD) is a chronic, occlusive cerebrovascular disease characterized by progressive stenosis of intracranial arteries, specifically the internal carotid arteries, and the compensatory formation of an abnormal vascular network at the base of the brain. The exact cause of MMD is still not well understood. Many factors including genetic, environmental, and immunologic have been associated with the disease. RNF213 is considered the main susceptibility gene, especially in Eastern Asian patients. The founder mutation, p.R4810K, has been associated strongly with MMD, especially in Japan and Korea but has been shown to have low penetrance and has never been described in non-Eastern Asian MMD cases. RNF213 encodes for an E3 ubiquitin-protein ligase with ATPase activity. It has described to regulate angiogenesis giving rise to the possibility that variants in RNF213 may play a role in cerebrovascular diseases other than MMD. OBJECTIVES: The aims of this study were to determine if variation in the RNF213 gene contributes to MMD in a cohort of 15 unrelated patients with MMD of predominantly European descent, to investigate other potential genes implicated in MMD in these 15 patients, and to investigate if RNF213 also influences more common vascular phenotypes. METHODS: Patient history, detailed family history and a blood sample were collected from 15 patients with well-characterized MMD. DNA was extracted from a peripheral venous blood sample, assessed for quality, and DNA concentration quantified by PicoGreen®. The extracted DNA was sent for whole exome sequencing. Genome_GPS_2.0 was used to carry out secondary analysis of sequencing data and all data were stored in Oracle TRC. The files were aligned using Novoalign, variants analyzed using GATK, visualized using IGV and annotated using BioR-Web. Variants of interest were determined using Ingenuity® Variant Analysis™. To determine if RNF213 also influences more common vascular phenotypes, previously collected and whole exome sequenced samples from the Mayo Clinic Florida Familial Cerebrovascular Diseases Registry were analyzed. Variants in RNF213 were determined using the same approach as for MMD. RESULTS: Likely pathogenic variants in RNF213 were found in 13% (2/15) of patients. The p.R4810K variant has been previously published as the founder mutation for MMD in Eastern Asian populations. The affected patient was also of Eastern Asian origin. The other variant, p.R4019C, was found in a European descent case and has been described as a candidate pathogenic variant. Eight variants in five other genes previously associated with MMD were found. Of these, one previously reported variant, p.D455H in RPTN, was found in two patients. The other seven have not previously been described in MMD. In the analysis of the potential role for RNF213 in other cerebrovascular diseases, 54% (22/41) of African American patients had a non-synonymous, exonic variant in RNF213 with a MAF of less than 3%. A novel RNF213 variant was also found in a Caucasian patient who had a subarachnoid hemorrhage. CONCLUSION: The p.R4810K variant in RNF213 was confirmed to only be associated with MMD in Eastern Asians and not found in other ethnicities. However, a variant in RNF213 was found in a Caucasian patient suggesting RNF213 may indeed be disease causing in patients of diverse origin. RNF213 may also be implicated in other cerebrovascular diseases suggesting a common pathogenesis while other genes also appear to be involved in the pathogenesis of MMD.