27. Can I test a pregnancy to see if my unborn child will be affected?

Prenatal Diagnosis

Prenatal Diagnosis (PND) involves removing cells or fluid during early pregnancy to test for a known mitochondrial mutation and is usually performed using one of 2 techniques.

CVS (Chorionic villus sampling) is usually performed at around 11-12 weeks of pregnancy and involves removing and testing a sample of cells from the placenta to see if they carry the mitochondrial mutation.

Amniocentesis is usually performed at around 15-18 weeks of pregnancy and involves removing a sample of amniotic fluid to see if the cells carry the mitochondrial mutation.

For nuclear DNA mutations, both CVS and amniocentesis can give a very accurate determination as to whether the baby carries the faulty gene and can therefore give an accurate risk of the baby inheriting Mitochondrial Disease.

For Mitochondrial DNA mutations it is slightly more complicated as the severity of disease depends on the number of faulty mitochondria or 'mutant load'. Individuals tolerate similar mutant loads differently and also the level at which the mutant load in cells may cause problematic symptoms varies for different types of tissue in the body, making it very difficult to determine a prognosis.

In these cases it is certainly important to understand the results of CVS in light of how other individuals in the family have been affected and the level of 'mutant load' at which they were affected.

Preimplantation Genetic Diagnosis (PGD)

This is a process used in combination with IVF techniques where one or more cells are removed from the early embryo for genetic testing.

For nuclear DNA mutations, PGD can give a very accurate determination as to whether the embryo carries the faulty gene and so only unaffected embryos will be implanted back into the mother to try and establish a pregnancy.

For Mitochondrial DNA mutations again it is slightly more complicated as the severity of disease depends on the number of faulty mitochondria or 'mutant load'. Individuals tolerate similar mutant loads differently and also the level at which the mutant load in cells may cause symptoms varies for different types of tissue in the body making it very difficult to determine a prognosis. 

Clinical experience in the UK suggests that for PGD, a mutant load of 30% or less should result in asymptomatic or unaffected individuals.

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