Editor—Since the first report by Mankinenet al 1 in 1976, over 30 cases with microscopically visible 1q deletions have been described. Patients with a distal deletion of 1q (q42 or q43→qter) have a recognisable pattern of malformations, albeit rather variable.2 3 The facial features include microcephaly, a full, round face with prominent forehead (sometimes with a metopic ridge), upward slanting palpebral fissures, epicanthic folds, a short, broad nose with a flat nasal bridge, thin lips with downturned corners of the mouth, micrognathia, apparently low set ears, and an abnormal palate (sometimes cleft). Patients are mentally and growth retarded, and may have variable cardiac, genital, and central nervous system anomalies. As most of these features suggest a chromosomal abnormality, patients with a deletion of distal 1q will usually be diagnosed after routine karyotyping. However, for submicroscopic distal 1q deletions, fluorescence in situ hybridisation with a 1qter specific probe will be required for the cytogenetic diagnosis. This test needs to be specially requested. In recent years, in situ hybridisation has led to the awareness that subtelomeric deletions below the level of the light microscope (<2-3 Mb) are a significant cause of malformation and mental retardation. One study identified previously undetectable abnormalities in 5% of 99 retarded patients.4 Whereas large deletions of distal 1q have been reported frequently, no submicroscopic distal 1q deletions have been described so far. Here we report the clinical and cytogenetic findings in two unrelated mentally retarded boys and one female fetus, one with a submicroscopic distal 1q deletion and the others with a partial submicroscopic trisomy of distal 13q in addition to a submicroscopic distal 1q deletion.

The first patient is a 7 year old boy who was born at 39 weeks' gestation with a low birth weight of 2300 g (<3rd centile). …