PRKDC and severe combined immunodeficiency due to DNA-PKcs deficiency: Recessive biallelic mutations in the PRKDC gene that expresses the catalytic portion of DNA-PK (known as DNA-PKcs) cause IMD26 (Immunodeficiency 26, OMIM 615966), a syndrome that can be accompanied by neurological manifestations, including microcephaly, seizures, and hearing and vision losses.