SLC7A6OS Founder Mutation: A Rare Cause of Progressive Myoclonus Epilepsy Dated to 1100 Years Ago

BACKGROUND: SLC7A6OS c.191A>G is a rare, autosomal recessive cause of progressive myoclonus epilepsy (PME). The c.191A>G variant, first discovered in two families from Türkiye and Portugal, was recently identified in three additional probands from the USA, all of Puerto Rican ancestry. OBJECTIVES: We sought to refine the SLC7A6OS-PME phenotype and determine whether all families inherited the variant from the same common ancestor. METHODS: Clinical and genotyping data were obtained from all five families. Haplotype analysis using single nucleotide polymorphism arrays to investigate a possible common ancestor was performed. RESULTS: Shared haplotypes suggest all five families inherited the SLC7A6OS variant from a common ancestor approximately 1100 years ago. Subsequent dating estimates were consistent with migration patterns between the eastern Mediterranean, Iberia, and Puerto Rico. CONCLUSIONS: Our findings strengthen the previous evidence for SLC7A6OS as a cause of PME and highlight a founder effect in regions with migratory links to Iberia.