Severe Combined Immunodeficiency with Microcephaly, Growth Retardation, and Sensitivity to Ionizing Radiation, also known as cernunnos-xlf deficiency, is related to severe combined immunodeficiency and microcephaly. An important gene associated with Severe Combined Immunodeficiency with Microcephaly, Growth Retardation, and Sensitivity to Ionizing Radiation is NHEJ1 (Non-Homologous End Joining Factor 1). Affiliated tissues include cortex, and related phenotypes are microcephaly and growth delay