PGT-M

PGT-M (preimplantation genetic testing for monogenic disorders) is the genetic profiling of embryos before implantation to detect a specific inherited single-gene disease, so that only embryos free of the known disorder are transferred. It is an application of preimplantation genetic diagnosis and, because it needs embryos to test, is an adjunct to assisted reproductive technology that requires in-vitro fertilisation to obtain the oocytes or embryos. A key advantage is that, by selecting unaffected embryos before pregnancy begins, it can avoid the need for selective abortion, making it highly likely that the baby will be free of the disease under consideration. PGT-M is used for couples known to carry single-gene (monogenic) disorders, including autosomal recessive, autosomal dominant and X-linked conditions, as well as certain chromosomal structural rearrangements such as balanced translocations. Among the conditions frequently tested are autosomal recessive diseases such as cystic fibrosis, beta-thalassemia, sickle cell disease and spinal muscular atrophy type 1, and dominant conditions such as myotonic dystrophy, Huntington's disease and Charcot-Marie-Tooth disease. Embryos are generally sampled by biopsy at the blastocyst stage, around day 5 or 6 of development, which is gentler on the embryo than earlier cleavage-stage biopsy, and the DNA is analysed for the specific mutation. Unlike aneuploidy screening, which counts chromosomes, PGT-M looks for a defined genetic mutation in couples at known risk. As an invasive test performed on the embryo, it requires serious consideration.