Pregnancy after preimplantation genetic diagnosis for Holt Oram Syndrome (HOS)
Iacobelli M.1, Greco E.1, Brardinoni L.2 , Biricik A.3, Baldi M.3, Rienzi L.1, Ubaldi F.1, Ferrero S1, Nuccitelli A.2, Podini D.2 , Martinez F1 and Fiorentino F.2,3
1 Reproductive Medicine European Hospital, Rome, Italy
, Via Portuense 700, 00148 Rome, Italy
2 GENOMA- Molecular Genetics Laboratory - Via Po 102, 00198 Rome, Italy
3 EmbryoGen – Preimplantation Genetic Diagnosis Centre - Via Po 102, 00198 - Rome – Italy
AIMS: Holt-Oram Syndrome (HOS), (MIM 142900) is a rare genetic disorder, occurring at a frequency of 1 in 100,000 live births, characterized by distinctive bones and thumbs (upper limbs) malformations and heart abnormalities. HOS is caused by a mutation at heterozygote state of the TBX5 gene (12q21.3-q22). Approximately 60 percent of HOS cases receive the mutated gene from an affected parent, while in about 40 percent of the cases the disorder is a result of a de novo mutation. As there is no effective treatment of this disease, preimplantation genetic diagnosis (PGD) may be a useful option, for couples at risk, to establish a TBX5 mutation-free pregnancy. The aim of this study was to develop a new applicable strategy for HOS PGD.
METHODS: A couple with the female partner affected by HOS, was referred to our centre for PGD. The DNA sample was isolated from peripheral blood of the affected parent and different primers were designed to amplify the 9 exons of the gene. Screening for the identification of the disease causing mutation was performed by direct sequencing. PGD involved a minisequencing-based mutation analysis of the biopsied blastomeres, with simultaneous testing of three closely linked markers D12S1646, D12S129, and D12S1330 for ADO evaluation and also to detect potential contamination occurrence.
RESULTS: A “de novo” mutation was identified in exon 9 of the TBX5 gene in the affected parent. This mutation involves a heterozygous G → A transition that causes a change Trp → STOP, and resulted not yet described in literature. A single PGD cycle was performed, involving the fertilization of 6 oocytes, all of them developed into good quality embryos useful for the biopsy. Two embryos resulted unaffected, and were transferred back to the patient, yielding a singleton ongoing pregnancy at 20 weeks of gestation confirmed as healthy by prenatal diagnosis.
CONCLUSION: Although HOS is not a fatal disease and the disorder does not affect normal life expectancy, its clinical outcome makes it a good candidate for the development of PGD cycles. The first PGD for HOS could avoid couples such as the patients in question to have to consider pregnancy termination following a positive prenatal diagnosis. The single cell assay developed here may give hope to couples who find themselves in a similar situation.