OBJECTIVETo study the clinical features and to identify homeobox D13 (HOXD13) gene mutation of the affected individuals in a Chinese synpolydactyly (SPD) kindred.

METHODSClinical data and peripheral blood samples of SPD family members were obtained through field investigation. For every member of this pedigreeìthe fragment containing mutational hot spots of HOXD13 was amplified by PCR for mutation screening. To examine whether there is any other mutation within coding sequence of HOXD13, exon 1 and exon 2 of HOXD13 were also amplified by PCR. All the amplified fragments were electrophoresed on 2% agarose gels and then the mutant fragments were electrophoresed on 5% polyacrylamide gels to be separated. Purified PCR products of normal and selected mutant alleles were directly sequenced.

RESULTSComparing the HOXD13 coding sequence of the affected individuals with HOXD13 sequence in the GenBank and with that of the unaffected, an inserted segment coding 8 alanine residues within HOXD13 was found segregating with the disorder. This mutation is also termed polyalanine expansion. The 8-alanine expansion can be interpreted as a reduplication of normal alanines 5-12.

CONCLUSIONThe results suggest that synpolydactyly in this kindred may be caused by polyalanine expansion in HOXD13.