Filamin A Variant as a Possible Second-Hit Gene Promoting Moyamoya Disease–like Vascular Formation Associated With RNF213 p.R4810K Variant

BACKGROUND AND OBJECTIVE: The objective of this case report was to identify a second-hit gene that may promote Moyamoya disease (MMD)–like vascular formation in an individual having the RNF213 p.R4810K variant. METHODS: We performed magnetic resonance imaging and genetic analyses of RNF213 and FLNA in a 21-year-old woman, who showed Ehlers-Danlos–like symptoms and developed a first-ever unprovoked seizure, and of her healthy parents. RESULTS: We identified bilateral periventricular nodular heterotopia (PNH) as the cause of seizures and MMD-like vascular formation in the patient. The patient had the RNF213 p.R4810K variant. Exome analysis identified c.4868delG in the X-linked FLNA gene encoding filamin A p.G1623V fs*41, which could explain PNH and Ehlers-Danlos–like symptoms. Her mother had the same FLNA variant and had asymptomatic bilateral PNH, whereas her father had the RNF213 variant and had normal cerebrovascular structure. DISCUSSION: The family study suggested that the FLNA variant promoted MMD-like vascular formation in a patient having the RNF213 variant, while the RNF213 variant amplified the phenotypic changes elicited by the FLNA abnormality. Collectively, we identified a gene abnormality in filamin A, a target of RNF213-mediated proteasomal degradation, that may promote MMD-like vascular formation as a possible second-hit gene in individuals having the RNF213 p.R4810K variant.