Objective: To identify the causative mutations in two Chinese Han families featuring triphalangeal thumbs (TPT) and preaxial polydactyly (PPD).
Methods: Blood samples were collected from 9 members (2 affected) from family 1 and 14 members (7 affected) from family 2. After genomic DNA was extracted, the ZPA regulatory sequence (ZRS) region was analyzed with real-time quantitative PCR (qPCR) and Sanger sequencing. For family 1, haplotypes compassing the ZRS were also analyzed with short tandem repeats (STR) and single nucleotide changes.
Results: No copy number mutation around the ZRS region was found in both families. Two heterogeneous mutations in the ZRS (406A>G and 105C>G) were found to co-segregate with the TPT/PPD malformation in family 1 and 2, respectively. Neither mutation was detected in 200 healthy individuals. Haplotype analysis and Sanger sequencing of family 1 indicated that the first TPT/PPD patient in the family was both germline and somatic mosaic for the 406A>G mutation.
Conclusion: Two pathogenic ZRS mutations, 105C>G and 406A>G, have been identified in two Chinese Han families with TPT/PPD, among which the 406A>G mutation was de novo.