A group of rare genetic disorders of carbohydrate metabolism characterized by neurologic dysfunction; often affects other organ systems. Genetically and phenotypically diverse. Classified as disorders of N-glycosylation and O-glycosylation. The most common type is phosphomannomutase 2 congenital disorder of glycosylation (PMM2-CDG, CDG-1a), a disorder of N-glycosylation. This type has varied presentations and degrees of severity. Infants may present with ataxia, developmental delay, failure to thrive, and strabismus. Other symptoms include hyporeflexia, esotropia, axial hypotonia, poor feeding, vomiting, growth retardation, retinitis pigmentosa, and cerebellar hypoplasia. Childhood findings include intellectual disability and the inability to walk. Adolescent and adult patients present with neuromuscular and skeletal abnormalities and impaired sexual development (females).

Management is focused on treating symptoms, providing supportive services and devices, and monitoring to prevent complications.