Genetic variants of the COASY gene are responsible for a broad spectrum of clinical phenotypes, ranging from an invariable lethal phenotype with prenatal onset pontocerebellar hypoplasia, microcephaly, and arthrogryposis (PCH12), to neurological and neurodegenerative diseases characterized by heterogeneous symptoms and variable onset in childhood and adulthood (CoPAN). The gene discussed is COASY; the disease is arthrogryposis.