Diagnostic yield of chromosome analysis in patients with developmental delay or mental retardation who are otherwise nondysmorphic.

There is a standard recommendation that chromosomes be obtained in any patient who presents with developmental delay (DD) or mental retardation (MR) regardless of whether or not they have dysmorphic features. Increasingly, if patients are physically well-formed, the option to perform a karyotype is questioned because of the presumed low yield of a chromosomal abnormality. We hypothesize that patients with DD/MR who are non-dysmorphic do not have abnormal chromosomes at a rate high enough to warrant obtaining a karyotype on all patients in this population. A retrospective analysis of patients with DD/MR who were non-dysmorphic was performed. The total number of subjects was 134. Of these, 120 patients were recommended to have high-resolution chromosomes performed, among whom seven were lost to follow-up. In the remaining 113 patients, all had normal karyotypes. Three subjects were found to have fragile X syndrome, accounting for 3% of the males. One subject had a pathological mutation in MECP2. Our yield of chromosome analysis in non-dysmorphic patients with DD/MR is less than that previously described. The role of array-comparative genomic hybridization (array-CGH) as an auxiliary or alternative procedure in this patient population will be discussed.