POSITIONAL MAPPING OF LOCI IN THE DIGEORGE CRITICAL REGION AT CHROMOSOME 22Q11 USING A NEW MARKER (D22S183)

The majority of patients with DiGeorge syndrome (DGS) and velo-cardio- facial syndrome (VCFS) and a minority of patients with non-syndromic c onotruncal heart defects are hemizygous for a region of chromosome 22q 11. The chromosomal region that is commonly deleted is larger than 2 M b. It has not been possible to narrow the smallest region of overlap ( SRO) of the deletions to less than ca 500 kb, which suggests that DGS/ VCFS might be a contiguous gene syndrome, The saturation cloning of th e SRO is being carried out, and one gene (TUPLE1) has been identified. By using a cosmid probe (M51) and fluorescence in situ hybridization, we show here that the anonymous DNA marker locus D22S183 is within th e SRO, between TUPLE1 and D22S75 (probe N25). A second locus with weak homology to D22S183, recognized by cosmid M56, lies immediately outsi de the common SRO of the DGS and VCFS deletions, but inside the SRO of the DGS deletions. D22S183 sequences are strongly conserved in primat es and weaker hybridizing signals are found in DNA of other mammalian species; no transcripts are however detected in polyA(+) RNA from vari ous adult human organs. Probe M51 allows fast reliable screening for 2 2q11 deletions using fluorescence in situ hybridization. A deletion wa s found in 11 out of 12 DGS patients and in 3 out of 7 VCFS patients. Two patients inherited the deletion from a parent with mild (atypical) symptoms.