A Japanese Family with a Novel Pathogenic Variant in KIF1A Presenting with Spastic Paraparesis, Cerebellar Ataxia, and Intellectual Disability.

Variants in KIF1A are associated with hereditary spastic paraplegia (SPG30), which can manifest in both pure and complex forms. We describe a Japanese family with a novel KIF1A variant presenting with a complex form of SPG30. Patient 1, a 69-year-old woman, experienced progressive gait disturbance due to spastic paraparesis and cerebellar atrophy, and intellectual disability. Patient 2, the daughter of Patient 1, exhibited similar symptoms with more severe dysarthria. Patients 1 and 2 shared a heterozygous c.173 C > G (p.Ser58Trp) variant in the motor domain of KIF1A (NM_001244008.2), which is classified as likely pathogenic. This family highlights the role of autosomal dominant inheritance in a complex form of SPG30, expanding the understanding of its genetic basis and clinical presentation.