MAPPING OF 2 GENES ENCODING ISOFORMS OF THE ACTIN-BINDING PROTEIN ABP-280, A DYSTROPHIN LIKE PROTEIN, TO XQ28 AND TO CHROMOSOME-7

ABP-280 is a ubiquitous actin binding protein present in the cytoskele ton of many different cell types. ABP-280 was mapped to distal Xq28, 5 0-60 kb downstream of the Green Colour Pigment (GCP) genes. To establi sh if ABP-280 may be a candidate for one of the muscle diseases locali zed by linkage analysis to distal Xq28 we looked for alternative forms of ABP-280 mRNA. Several different ABP-280 mRNAs were indeed identifi ed: two are X-linked and are produced by alternative splicing of a sma ll exon of 24 nucleotides. At least one additional gene encoding a RNA more than 70% identical to ABP-280 in the 1700 bp sequenced has also been found. It was mapped to chromosome 7. While both forms of the X-l inked ABP-280 are ubiquitous, the gene on chromosome 7 is highly expre ssed only in sketetal muscle and heart. The two genes were therefore e xcellent candidates for the X-linked and for the autosomal dominant fo rm of the Emery-Dreifuss Muscular Dystrophy (EDMD) both of which have been described. So far, however we were unable to demonstrate mutation s in the coding region or affecting the alternative splicing of the X- linked form of ABP-280, in several patients studied, and we think that it is quite unlikely that this is the gene responsible for EDMD.