Monomelic amyotrophy, also known as Hirayama disease, is characterized by insidious onset of weakness and wasting of the muscles of the hand and forearm. It is usually unilateral, but can be bilateral. It occurs most commonly as a sporadic condition, is most common in young men, and follows a relatively benign course after a few years of progression (Nalini et al., 2004; Misra et al., 2005).

PI4KA-related disorder is a clinically variable disorder characterized primarily by neurologic dysfunction (limb spasticity, developmental delay, intellectual disability, seizures, ataxia, nystagmus), gastrointestinal manifestations (multiple intestinal atresia, inflammatory bowel disease), and combined immunodeficiency (leukopenia, variable immunoglobulin defects). Age of onset is typically antenatal or in early childhood; individuals can present with any combination of these features. Rare individuals present with later-onset hereditary spastic paraplegia. Brain MRI findings can include hypomyelinating leukodystrophy, cerebellar hypoplasia/atrophy, thin or dysplastic corpus callosum, and/or perisylvian polymicrogyria.