 In humans, mutations in the XRCC4 gene cause microcephalic primordial dwarfism, a phenotype characterized by marked microcephaly, facial dysmorphism, developmental delay and short stature.Although immunoglobulin junctional diversity is impaired, these individuals do not show a recognizable immunological phenotype.In contrast to individuals with a LIG4 mutation, pancytopenia resulting in bone marrow failure is not observed in individuals with XRCC4 deficiency.