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Brachydactyly type A2(BDA2,MIM 112600) ischaracterized by the deviation andshortening of the middle phalange of the index finger and the second toe.We carried out ageneticanalysis using a Chinese BDAZ family to give genetic heterogeneity.In the pedigree,we mappedthe the maximum candidate interval of BDA2 to a一1.5Mb region between D20S194 and D20S115within chromosome20p12.3,and found that the pairwise logarithm of odds score was highest formarker D20S156(Zmax=6.09atθ).Based on functional and positional perspectives,Bonemorphogenetic protein 2(BMP2) gene was identified as the causal gene for BDA2 in this regionthough no point mutation was detected in BMP2.With the further investigation,weidentified a 4.6kb genomic duplication atthe downstream of BMP2 gene.This duplication is located within thelinked region,co-segregated with the BDA2 phenotype in this family but not in the unaffectedfamilymembers and the unrelated control individuals.In summary,we detected a duplicationof 4.6kb in BMP2 locus in a Chinese family affected with BDA2.Our finding supportsthat the genomiclocation that correspondsto the duplication region is a mutationalhotspot and that this genomiclocation is critical for the function of BMP2.