[Clinical and molecular cytogenetic analysis of a family with mental retardation caused by an unbalanced translocation involving chromosomes 3 and 22].

OBJECTIVE:To explore the genetic cause of a Chinese boy with unexplained mental retardation, and analyze the pattern of inheritance for his family. METHODS:Routine karyotyping, chromosomal microarray analysis (CMA), and fluorescence in situ hybridization (FISH) were used to detect chromosome abnormalities in the patient and his families. RESULTS:Chromosome analysis suggested that the proband and 7 affected individuals had an identical karyotype 46,XN,der(22)t(3;22)(q28;q13)pat, while his father and 5 other relatives carried a same karyotype of 46,XN,t(3;22)(q28;q13). His mother and other family members were normal. CMA analysis confirmed that the patient had a 9.0 Mb duplication at 3q28q29, in addition with a 1.7 Mb deletion at 22q13.3. Above results were confirmed by FISH. CONCLUSION:The abnormal phenotypes of the proband and his family members from five generations have conformed to those of 3q duplication and 22q13.3 deletion caused by unbalanced translocation involving chromosomes 3q and 22q. The presence of multiple patients in this family may be attributed to abnormal gametes produced by parental balanced translocations involving 3q and 22q.