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 pregnancy to test for a known mitochondrial mutation and it 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 defective 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 causes 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.
Pre-Implantation Genetic Diagnosis (PGD)
This is a process used in conjunction with IVF technology where one or more cells are removed from the embryo for genetic testing.
For nuclear DNA mutations, PGD can give a very accurate determination as to whether the embryo carries the defective gene and so only unaffected embryos will be implanted back into the mother to continue to 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 causes problematic 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 results in asymptomatic or unaffected individuals.
