Screening for subtelomeric chromosome abnormalities in children with idiopathic mental retardation using multiprobe telomeric FISH and the new MAPH telomeric assay

Subtelomeric chromosomal abnormalities are emerging as an important cause o f human genetic disorders. The scope of this investigation was to screen a selected group of children with idiopathic mental retardation for subtelome ric anomalies using the multiprobe telomeric FISH method and also to develo p and test a new assay, the MAPH telomeric assay, in the same group of pati ents. The new MAPH telomeric assay uses the recently published MAPH methodo logy that permits the measurement of locus copy number by hybridisation wit h a specifically designed set of probes located at the end of human chromos omes. Seventy patients with idiopathic mental retardation have been screene d using the established multiprobe telomeric FISH assay and the new MAPH te lomeric assay, for all telomeres. One patient with de novo 8p subtelomeric deletion was identified. The new MAPH telomeric assay confirmed the same re sults in both normal and abnormal samples. This is the first description of the use of MAPH methodology to detect chromosomal imbalances near the telo meres in idiopathic mentally retarded patients. The new MAPH telomeric assa y offers a new, fast, accurate and cost effective diagnostic tool to detect chromosomal imbalances near telomeres in mentally retarded patients, as we ll as the characterisation of known chromosomal abnormalities, spontaneous recurrent miscarriages, infertility, hematological malignancies, preimplant ation genetic diagnosis, and other fields of clinical and research interest s.