RESUMEN
Brachydactyly type B (BDB) is an autosomal dominant disease caused by mutations in the ROR2 gene. Truncating mutations lead to the severe form of the disease, which is characterized by terminal deficiency of fingers and toes. Preimplantation genetic diagnosis (PGD) was carried out in a family suffering from severe BDB. The family was screened for mutations in exons 8 and 9 and found to harbour a known nonsense mutation (c.2265C-->A) in exon 9 of the ROR2 gene, which resulted in a premature stop-codon at residue 755. Three out of 10 linked markers tested were informative for this family and single cell work-up showed amplification efficiency in over 98% of the cells. Allele drop-out (ADO) was found in 0, 4.08 and 6.1% for D9S1803, D9S1842 and D9S280 respectively. The family underwent PGD using multiple displacement amplification, fluorescent polymerase chain reaction (informative short tandem repeat) and sequencing of exon 9. Two cells were taken from the three embryos generated in the PGD cycle and the diagnosis of both cells separately showed one normal embryo free of BDB abnormal allele. This embryo was transferred back to the mother and resulted in a singleton pregnancy. Postnatal DNA testing of the newborn confirmed the PGD result.