SECTION 4: PRENATAL STUDIES
Prenatal tests for families who have a child with Pitt-Hopkins syndrome.
The chance of parents who have a child with PTHS having a second child with PTHS is low – estimated to be about 2%. But because the chance is not zero, parents who have further pregnancies will want to know about whether their unborn baby can be tested for Pitt-Hopkins.
Although an expectant mum will be offered ultrasound scans, it won’t be possible to diagnose PTHS this way as there are usually no signs or symptoms in a developing baby that can be seen on a scan. The prenatal tests for Pitt-Hopkins are genetic tests and they look for a change in TCF4, the gene that causes Pitt-Hopkins. Any parents whose child has been found to have a genetic change that causes Pitt-Hopkins can be offered prenatal tests in any further pregnancies to see if the same genetic change is present in the unborn baby. Prenatal testing for Pitt-Hopkins in these cases is very reliable.
Health care professionals should discuss prenatal testing with parents during any subsequent pregnancies and offer it if parents want to go ahead.
The tests can be carried out in different ways:
* a sample of cells is taken from the placenta (chorionic villi biopsy)
* a sample of cells is taken from the fluid that surrounds the unborn baby in the womb (amniocentesis)
* testing is done during in vitro fertilisation (IVF), when an egg from a woman is fertilised by sperm in a laboratory.
Nowadays it’s possible to check for changes in large series of genes in the mother’s blood during a pregnancy, as there is always a bit of the baby’s DNA present in the mother’s blood too. (known as non-invasive, cell-free foetal DNA screening.) It would be possible to check the TCF4 gene in this as well and therefore also in a family with no child with PTHS.
However, both parents’ DNA would be needed for this and doctors are often uncertain whether a change in a gene is a variant of normal (in medical terms: polymorphism) or really causing harm. Because of this uncertainty, the group of experts who created these guidelines concluded that such testing is only useful for a family who have a child with PTHS, and not for families who do not.
Recommendations
6/ If a family has a child with PTHS, confirmed by DNA testing, health care professionals should discuss with parents the small chance of having another child with the syndrome, and discuss and offer prenatal testing.
7/ Prenatal testing for PTHS should not be offered to parents unless they already have a child with the syndrome, as there are problems in interpreting the findings in a reliable way.