Disseminated superficial actinic porokeratosis (DSAP) is an uncommon autosomal dominant keratinization disorder with genetic heterogeneity characterized by multiple superficial keratotic lesions surrounded by a slightly raised keratotic border. Thus far, there have been three susceptible loci determined for DSAP and one locus for disseminated superficial porokeratosis (DSP), i.e. 12q23.2-24.1, 15q25.1-26.1, 1p31.3-p31.1 and 18p11.3. Moreover, the locus for porokeratosis palmaris plantaris et disseminata (PPPD) was mapped to 12q24.1-24.2, which overlapped with the first DSAP locus. Following the exclusion of these known loci in a four-generation Chinese DSAP family, we performed a genome-wide linkage analysis and identified a new locus on chromosome 16q24.1-24.3. The maximum two-point LOD score of 3.73 was obtained with the marker D16S3074 at a recombination fraction θ of 0.00. Haplotype analysis defined the critical 17.4-cM region for DSAP between D16S3091 and D16S413. This is regarded to be the forth locus for DSAP (DSAP4). ATP2C1 was sequenced as a candidate gene, however, no mutation was found. Further investigation for the genetic basis of DSAP is under way.
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