Preimplantation genetic diagnosis of skin fragility-ectodermal dysplasia syndrome.
Skin fragility-ectodermal dysplasia syndrome is an autosomal recessive disorder caused by loss-of-function mutations in the desmosomal protein, plakophilin 1. Clinically, there may be considerable morbidity from extensive skin erosions and painful fissures on the palms and soles. In the absence of any specific treatment, prenatal diagnosis is an option for couples at reproductive risk of recurrence. In 2000, we developed and applied a single cell nested polymerase chain reaction protocol to test one couple for compound heterozygous plakophilin 1 gene mutations by preimplantation genetic diagnosis (PGD). Although pregnancy was established, an unrelated trisomy 22 led to a spontaneous abortion. However, eight embryos of known genetic status were cryopreserved at that stage, and we planned to undertake subsequent frozen embryo replacement cycles that might lead to the birth of an unaffected child in this family. Embryo cryopreservation was carried out in June 2000 using standard protocols in a three-step freezing procedure. Four embryos were thawed in March 2003, one of which was viable and was used in a frozen embryo replacement cycle, but pregnancy did not occur. The remaining four embryos were thawed in February 2004, two of which were viable (both carriers of the paternal mutation) and these were used in a second frozen embryo replacement cycle, and a singleton pregnancy was established. The child's plakophilin 1 genotype was assessed by direct nucleotide sequencing across the site of both potential mutations. Following two frozen embryo replacement cycles, and almost 4 years after the initial embryo biopsy and mutation analysis, a pregnancy was achieved that progressed to term with the birth of a healthy baby girl. Nucleotide sequencing of cord blood DNA, taken immediately after delivery, showed that the child was a heterozygous carrier of the paternal mutation but not of the maternal mutation. This case demonstrates the value of embryo cryopreservation, which can increase the number of embryo replacement procedures and hence the cumulative pregnancy rate per retrieval cycle. Moreover, this is the first report of successful full-term pregnancy and birth of a healthy baby following exclusion of a severe genodermatosis by PGD. The successful outcome of PGD in this case illustrates what is technically possible for couples at risk of recurrence of a severe inherited skin disease.