Exome sequencing of two sisters with congenital cataracts, short stature, and white matter changes identified compound heterozygous variants in the PISD gene, encoding the phosphatidylserine decarboxylase enzyme that converts phosphatidylserine to phosphatidylethanolamine (PE) in the inner mitochondrial membrane (IMM). The gene discussed is PISD; the disease is Developmental cataract.