The region on chromosome 7q21-22 is frequently altered in several human neoplasias such as uterine leiomyoma, myeloid leukemia and breast cancer. The same region has also been linked to split hand/split foot malformation type 1 and to involutional osteoporosis. Our analysis of genes that map to this region has led to the identification of the so far unknown first exon of the homeobox gene DLX6, a mammalian homologue of the Drosophila distal-less gene. Distal-less is a downstream target of the trithorax transcription factors. Translocations involving the mammalian homologue of trithorax, ALL-1, leading to its constitutive activation cause leukemia. We describe here that the first exons of human and mouse DLX6 genes contain a multiple trinucleotide repeat region. We have analyzed the CAG repeat length in 90 subjects and were able to identify five alleles with 11 to 20 CAG repeats.