[Genetic study of a child with developmental delay and mental retardation].

OBJECTIVE: To explore the genetic basis for a child with developmental delay and mental retardation. METHODS: Chromosomal karyotype of the child was analyzed by G-, C- and N-banding techniques. Her genome DNA was analyzed with single nucleotide polymorphisms array (SNP array). The result was validated by fluorescence quantitative polymerase chain reaction (PCR). RESULTS: The karyotype of the child was ascertained as 46,XX,r(22)(p12q13). SNP array has revealed a deletion of approximately 1.4 Mb at 22q13.33 (49 802 963-51 197 766). The deletion has encompassed the SHANK3, a crucial gene for the development of nervous system. Fluorescence quantitative PCR has confirmed the deletion of exons 7, 19 and 22 of the SHANK3 gene. CONCLUSION: The phenotype of the patient may be attributed to the microdeletion at 22q13.33. Cytogenetic methods combined with SNP array and fluorescence quantitative PCR can identify aberrant chromosomes and provide accurate information for the clinical diagnosis and genetic counseling.