The gene for May-Hegglin anomaly localizes to a < 1-mb region on chromosome 22q12.3-13.1

The May-Hegglin anomaly (MHA) is an autosomal dominant platelet disorder of unknown etiology. It is characterized by thrombocytopenia, giant platelets , and leukocyte inclusion bodies, and affected heterozygotes are predispose d to bleeding episodes. The MHA gene has recently been localized, by means of linkage analysis, to a 13.6-cM region on chromosome 22, and the complete chromosome 22 sequence has been reported. We recently performed a genome s can for the MHA gene in 29 members of a large, multigenerational Italian fa mily, and we now confirm that the MHA locus is on chromosome 22q12.3-13.1. The maximal two-point LOD score of 4.50 was achieved with the use of marker D22S283, at a recombination fraction of .05. Haplotype analysis narrowed t he MHA critical region to 6.6 cM between markers D22S683 and D22S1177. It i s of note that the chromosome 22 sequence allowed all markers to be ordered correctly, identified all the candidate genes and predicted genes, and spe cifically determined the physical size of the MHA region to be 0.7 Mb. Thes e results significantly narrow the region in which the MHA gene is located, and they represent the first use of chromosome 22 data to positionally clo ne a disease gene.