Gender Effects on the Clinical Phenotype in Japanese Patients with Spinal Muscular Atrophy

Spinal muscular atrophy (SMA) is a neuromuscular disease caused by a mutation in SMN1. SMA is classified into three subtypes (types 1, 2, 3) based on achieved motor milestones. Although NAIP and SMN2 are widely accepted as SMA-modifying factors, gender-related modifying factors or gender effects on the clinical phenotype are still controversial.A total of 122 Japanese patients with SMA, of which SMN1 was homozygously deleted, were analyzed from the perspective of the achieved motor milestone, NAIP status and SMN2 copy number.A predominance of male patients was observed in SMA type 3 (the walker group) without NAIP-deletion or with high SMN2 copy number (3 or 4 copies).We suggest the presence of gender-related modifiers on disease severity in SMA patients. The modifiers may contribute only in the presence of NAIP and a high copy number of SMN2.