OBJECTIVETo determine the origin of aberrant chromosomes involving the short arm of chromosome 8 in two mentally retarded children, and to correlate the karyotype with abnormal phenotype.

METHODSRoutine G-banding was performed to analyze the karyotypes of the two patients and their parents, and array comparative genomic hybridization (array CGH) was used for the first patient for fine mapping of the aberrant region.

RESULTSThe first patient presented with only mental retardation. The father had normal karyotype. The mother had an apparent insertion translocation involving chromosomes 8 and 3 [46, XX, inv ins (3; 8) (q25.3; p23.1p11.2)], the karyotype of the child was ascertained as 46, XX, der(3) inv ins (3; 8)(q25.3; p23.1p11.2). Array CGH finely mapped the duplication to 8p11.21-8p22, a 26.9 Mb region. The other patient presented with mental retardation, craniofacial defects, congenital heart disease and minor skeletal abnormality. The mother had normal karyotype. The father had an apparently balanced translocation involving chromosome 8p and 11q, the karyotype was 46, XY, t(8; 11)(p11.2; q25). The karyotype of the child was then ascertained as 46, XX, der(11)t(8; 11)(p11.2; q25).

CONCLUSIONThese results suggested that partial trisomy 8p was primary cause for the phenotypic abnormalities of the two patients, whereas a mild phenotypic effect was observed in patient 1. Parental karyotype analysis could help define the aberrant type and recurrent risk evaluation. In contract to routine karyotype analysis, aberrant regions could be mapped by array CGH with higher resolution and accuracy.