MOLECULAR-CYTOGENETIC DETECTION OF A DELETION OF 1P36.3

We report a deletion of 1p36.3 in a child with microcephaly, mental re tardation, broad forehead, deep set eyes, depressed nasal bridge, flat midface, relative prognathism, and abnormal ears. The phenotype is co nsistent with that described for partial monosomy for 1p36.3. Reverse chromosome painting and microsatellite and Southern blot analyses were used to map the extent of the deletion. Fluorescence in situ hybridis ation (FISH) analysis using probes from every telomere indicates that the rearrangement is likely to be a chromosomal truncation or rearrang ement involving subtelomeric repetitive DNA. The deletion was identifi ed by screening a sample of children and adults with idiopathic mental retardation. In conjunction with previous work on this sample, we est imate that 7.4% of the group have subtelomeric rearrangements.