Notably, complete loss‐of‐function COASY variants have been identified in a total of 13 fetuses/newborns with pontocerebellar hypoplasia type 12 (PCH12), which is characterized by a fatal perinatal outcome defined by pons and cerebellar atrophy, microcephaly, and arthrogryposis, but without evidence of brain iron accumulation.10, 11. Here, COASY is linked to microcephaly.