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We report a case of Miller-Dieker syndrome (MDS) owing to an unbalanced rearrangement of a familial pericentric inversion of chromosome 17 (inv(17) (p13.3q25.1)). In addition to lissencephaly and the facial features of MDS, the affected child had other congenital malformations consistent with distal 17q duplication. Initial cytogenetic analysis failed to show any abnormality and fluorescence in situ hybridisation (FISH) studies confirmed the 17p deletion in the proband and identified the chromosome 17 inversion in his mother. FISH studies were performed in other relatives and enabled first trimester prenatal diagnosis by chorionic villus sampling in a subsequent pregnancy of the proband's mother. These findings underline the value of FISH in the investigation of MDS families.

A female infant with peripheral pulmonary artery stenosis, growth retardation, and developmental delay was noticed to have facial features consistent with a diagnosis of Williams syndrome. Chromosome analysis revealed a deletion of the terminal portion of the long arm of chromosome 4 (4q33----qter). This is the seventh reported case of this chromosome disorder. It is possible that this chromosome region is specific for the Williams syndrome phenotype but it is more likely that the syndrome is heterogeneous. Chromosome analysis should be performed in all suspected cases with particular attention to the long arm of chromosome 4.