Incomplete penetrance with normal MRI in a woman with germline mutation ofthe DCX gene

X-linked isolated lissencephaly sequence (ILS) and subcortical band heterot opia are allelic human disorders associated with mutations of the DCX gene in both familial and sporadic forms. The authors describe a large Sardinian family in which three brothers with ILS have a missense mutation of the DC X gene. Their mother, a nonmosaic carrier, has a normal phenotype and crani al MRI, Skewed X-inactivation in the lymphocytes was also ruled out. This i s the first report of an asymptomatic carrier of a DCX mutation likely due to apparent nonpenetrance.