Translocation

Chromosomal abnormalities and IVF

A number of different chromosomal abnormalities in patients can lead to infertility. Usually these involve changes to the normal 46 pairs of chromosomes. These changes usually do not involve the gain or loss of any patient DNA and hence patients can carry these often without knowing and it is only when the experience infertility issues that a chromosome abnormality is identified. These abnormalities are usually found by looking at the chromosome of a carrier parent by Karyotyping (examining all the chromosomes to look for abnormalities). Chromosome abnormalities are carried by both men and women. Further details of chromosomal translocations and IVF go to Chromosome Screening.org

The different classes of abnormalities are described below.

Reciprocal translocation PGD

These abnormalities occur when two chromosomes exchange a large amount of their DNA. Hence there is an exchange but not usually a gain or loss of DNA providing the carrier patient is not developmentally or mentally delayed. When the carrier attempts to conceive, if one of the abnormal chromosomes is passed onto an egg or sperm then the resulting embryo will be chromosomally unbalanced. This usually leads to a miscarriage but if the abnormal chromosome has a gain or loss of a small proportion of a chromosome then this can in rare circumstances lead to an affected birth.

Reciprocal translocations are found in about 1:500 of the general population.

Genesis Genetics has pioneered the use of array CGH, much like PGS, to look at embryos of reciprocal translocation carriers. Genesis Genetics uses a higher resolution form of PGS to look for the small chromosomal imbalances that are seen in the embryos of reciprocal translocation carriers, thereby identifying not only embryos which are normal (euploid or balanced) for the chromosomes involved in the translocation, but also all the other chromosomes.

Once embryos are identified that are suitable for implantation, which is usually 15-20% of all embryos available, then very low miscarriage rates have been observed.

Further information on Reciporcal Translocations can be found at Unique the rare chromosomal disorder society.

Robertsonian Translocation PGD

The chromosomal abnormalities occur when two chromosomes are fused together. The chromosomes that become fused together are only the chromosomes which have one chromosome arm, termed “acrocentric” chromosomes, which includes any combination of chromosomes 13, 14, 15, 21, 22. Usually Robertsonian translocations are found in female carriers, who are physically normal, at about 1:1000 of the female population. If the Robertsonian Translcoation is passed on in the egg then it usually results in a chromosome gain in an embryo.

Identifying embryos of Robertsonian Translocation carriers via PGD with a normal number of chromosomes is highly feasible and these embryos can go on to produce a high pregnancy / live birth rate of unaffected babies. Genesis Genetics has performed PGD for hundreads of Robersonian translocation carriers.

The infertility risks associated with being a Robertsonian Translocation carrier vary from miscarriage to birth of a baby with an extra copy of a chromosome such as trisomy 21 or Downs syndrome.

Depending on your particular Robertsonian Translocation, Genesis Genetics can counsel you directly on the possible risks and outcomes.

Further information on Robertsonian Translocations can be found at Unique the rare chromosomal disorder society.

Inversions PGD

Inversion occur where there are two breaks within the same chromosome and a part of the chromosome is inverted (placed in line the wrong way around). As with the chromosome translocations (which involve different chromosomes) if there is no gain or loss of DNA then the carrier is usually physically normal and often inversions are only found when the carrier experiences infertility issues. Large inversions that can lead to infertility issues are rarer than translocations. The size and position of the inversion in a chromosome can affect the possible outcomes of any pregnancy hence it is recommended that you talk to a Genesis Genetics counsellor in order to provide you with details specific to your particular situation.

Further information on Robertsonian Translocations can be found at Unique the rare chromosomal disorder society.

De novo chromosomal abnormalities

Children are occasionally born and found to have developmental delay due to de novo chromosomal abnormalities. De novo means that the abnormality occurred during the process of conception, hence the abnormality is not carried by the parent. These abnormalities are usually  random and hence unlikely to be replicated in subsequent pregnancies and PGD is not recommended for these conditions.

About Us

Genesis Genetics is the pioneer of preimplantation testing of embryos for inherited genetic abnormalities, and was founded by world renowned scientists largely responsible for discovering preimplantation genetic diagnosis (PGD) as a clinical practice and performed the first successful cases in the world.

 

Contact Genesis Genetics

London Biosciences Innovation Centre
London NW1 0NH
Phone: +44 (0)20 7691 2084
Email: ggeulab1@genesisgenetics.org
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