Medical genetics diagnostic evaluation of the child with global developmental delay or intellectual disability

The review addresses the recent discovery of large-scale copy number variations in the human genome and advances in microarray technology which together have changed the clinical genetic diagnostic approach for children with global developmental delay.

Several publications in the last three years evaluate the diagnostic rate of array comparative genomic hybridization (aCGH) in the setting of global developmental delay; to date, the rate of etiologic diagnosis ranges from 4.8% to 20%, a potential doubling of the rate of diagnosis prior to the application of this technique.

Large-scale copy number variations in the human genome leading to gene dosage imbalances comprise approximately 12% of the entire genome and some 10% of all known genes. Molecular testing for chromosome imbalances has changed with the application of array comparative genomic hybridization. Recent publications suggest a doubling of the rate of diagnosis of patients with genome copy number abnormalities as the cause of developmental delay. The use of array comparative genomic hybridization is replacing the use of fluorescent in-situ hybridization techniques for the child with idiopathic global developmental delay or intellectual disability.