Abstract
Preimplantation genetic diagnosis (PGD), first successfully carried out in humans
in the early 1990s, initially involved the PCR sexing of embryos by Y- (and later
also X-) chromosome specific detection. Because of the problems relating to misdiagnosis
and contamination of this technology however the PCR based test was superseded by
a FISH-based approach involving X and Y specific probes. Sexing by FISH heralded translocation
screening, which was shortly followed by preimplantation genetic screening (PGS) for
Aneuploidy. Aneuploidy is widely accepted to be the leading cause of implantation
failure in assisted reproductive technology (ART) and a major contributor to miscarriage,
especially in women of advanced maternal age. PGS (AKA PGD for aneuploidy PGD-A) has
had a chequered history, with conflicting lines of evidence for and against its use.
The current practice of trophectoderm biopsy followed by array CGH or next generation
sequencing is gaining in popularity however as evidence for its efficacy grows. PGS
has the potential to identify viable embryos that can be transferred thereby reducing
the chances of traumatic failed IVF cycles, miscarriage or congenital abnormalities
and facilitating the quickest time to live birth of chromosomally normal offspring.
In parallel to chromosomal diagnoses, technology for PGD has allowed for improvements
in accuracy and efficiency of the genetic screening of embryos for monogenic disorders.
The number of genetic conditions available for screening has increased since the early
days of PGD, with the human fertilization and embryology authority currently licensing
419 conditions in the UK [1]. A novel technique known as karyomapping that involves
SNP chip screening and tracing inherited chromosomal haploblocks is now licensed for
the PGD detection of monogenic disorders. Its potential for the universal detection
of chromosomal and monogenic disorders simultaneously however, has yet to be realized.
Keywords
Preimplantation genetic screening - Preimplantation genetic diagnosis - Aneuploidy
- Fluorescent in situ hybridization - Karyomapping - Next generation sequencing
