(8) (2021) identified a neurodevelopmental disorder caused by homozygous or compound heterozygous mutations in the PI4KA gene in 10 unrelated patients, among whom patients 1–8 had shown the anomalies perisylvian polymicrogyria, cerebellar hypoplasia, and arthrogryposis (OMIM: 616531); patients 9 and 10 with compound heterozygous mutations in the PI4KA gene had autosomal recessive spastic paraplegia-84 (OMIM: 619621), which suggests that PI4KIIIα and phosphoinositide signaling played major roles in myelination and brain development. The gene discussed is PI4KA; the disease is spastic paraplegia 84, autosomal recessive.