Editor—Reports of patients with terminal de novo deletions of chromosome 15q26 are rare. Excluding cases of ring chromosome 15 formation with different sized deleted chromosomal segments, only seven cases with solely distal deletions of 15q have been published.1-7 All other cases resulted from unbalanced reciprocal translocations involving different chromosomes and are therefore not comparable with de novo terminal deletions as described in our case.

With two exceptions, all de novo cases had interstitial deletions between chromosomal bands 15q21-q25. Only the patients described by Roback et al 5 and Siebleret al 6 had terminal deletions of 15q26.1. The deletions in these patients were not investigated by FISH, but molecular genetic techniques showed the loss of one copy of the insulin-like growth factor 1 receptor gene. IGF1R is a tyrosine kinase containing transmembrane protein that plays an important role in cell growth control. It has been assumed that monozygosity for this gene, which maps to distal 15q26, will directly disturb this pathway and inhibit normal growth of patients.8

Today, in addition to classical cytogenetic banding methods, FISH techniques including comparative genomic hybridisation (CGH) can be used to provide a powerful tool to characterise chromosomal aberrations. In this study, we present the molecular cytogenetic findings and the detailed clinical phenotype of a girl with deletion 15q26.1 and compare these with other published cases. Our patient described here is, to the best of our knowledge, the second patient with a de novo terminal deletion at 15q26.1 and the first one well characterised by molecular cytogenetic techniques.