Abstract

Preimplantation genetic diagnosis (PGD) first consisted of the selection of female embryos for patients at risk of transmitting X-linked recessive diseases. Advances in molecular biology now allow the specific diagnosis of almost any Mendelian disease. For families with an identified X-linked recessive disease-causing mutation, non-specific diagnosis by sex identification can be considered as a sub-standard method, since it involves the unnecessary disposal of healthy male embryos and reduces success rate by diminishing the pool of embryos eligible for transfer. The most telomeric part of the X-chromosome long arm is a highly gene-rich region encompassing disease genes such as haemophilia A, X-linked adrenoleukodystrophy, X-linked hydrocephalus and incontinentia pigmenti. We developed five single-cell triplex amplification protocols with microsatellite markers DXS1073, DXS9901 (BGN), G6PD, DXS1108, DXS8087 and F8C-IVS13 located in this Xq terminal region. These tests allow the diagnosis of all diseases previously mentioned providing that the genetic material allowing the identification of the morbid allele can be obtained. The choice of the microsatellite set to use depends on the localisation of the gene responsible for the diagnosed pathology and on the informativity of the markers in particular families. Single-cell amplification efficiency was assessed on single lymphocytes. Amplification rate of the different markers ranged from 89-97% with an allele drop out rate of 2-19%. So far PGD has been carried out for three carrier females at risk of transmitting X-linked adrenoleukodystrophy, X-linked hydrocephalus and hemophilia A. The latter one is now pregnant.