HYCC1 encodes hyccin, a critical component of the phosphatidylinositol 4-kinase (PI4KA) complex required for plasma membrane localization and regulation of PI4K activity 1. The complex catalyzes conversion of phosphatidylinositol to phosphatidylinositol 4-phosphate (PI4P), a precursor of essential membrane phosphoinositides 2. HYCC1 is particularly important in oligodendrocytes, cells with dramatically expanded plasma membranes requiring substantial PI4P production for myelin membrane biogenesis 1. This function explains its critical role in central and peripheral nervous system myelination 31. Mutations in HYCC1 cause hypomyelinating leukodystrophy-5 (HLD5), a rare autosomal recessive disorder characterized by congenital cataracts, developmental delay, and progressive neurological impairment with hypomyelination visible on brain imaging 45. Clinical presentations range from severe early-onset disease to milder phenotypes, though genotype-phenotype correlations remain unreliable 46. Affected individuals demonstrate slowed motor nerve conduction velocities, increased central conduction times, and reduced myelinated fiber density in peripheral nerves 5. HYCC1 may additionally participate in beta-catenin/Lef signaling pathways 7, though this remains incompletely characterized.