Of interest this patient exhibits one of the most severe forms of MCSZ documented, with a level of microcephaly and growth retardation comparable to patients with ataxia telangiectasia and Rad3 related-Seckel Syndrome.16 Despite this, in keeping with the functional analysis of other identified PNKP mutations,15 cells derived from this patient retain some residual PNKP activity. This evidence concerns the gene PNKP and Ataxia-telangiectasia.