Causes of Patau's syndrome

Patau's syndromehappens by chance and isn't caused by anything the parents have done.

Most cases of the syndrome don't run in families (they're not inherited). They occur randomly during conception, when the sperm and egg combine and the foetus starts to develop.

An error occurs when the cells divide, resulting in an additional copy or part of a copyof chromosome 13, whichseverely affects the baby's development in the womb.

In many cases, the baby dies before reaching full term (miscarriage) or is dead at birth (stillbirth) .

In most cases of Patau's syndrome (75-90%), a baby has a whole extra copy of chromosome number 13 in their body's cells. This is sometimes known as trisomy 13 or simple trisomy 13.

In 5-10% of cases of Patau's syndrome, genetic material is rearranged between chromosome 13 and another chromosome. This is called a chromosomal translocation.

Patau's syndrome that arises because of this can be inherited. Genetic Alliance UK has more information about chromosome disorders .

In a further 5% of cases, only some cells have the extra copy of chromosome 13. This is known as trisomy 13 mosaicism. Occasionally, only part of one chromosome 13 is extra (partial trisomy 13).

The symptoms and features of both mosaicism and partial trisomy tend to be less severe than in simple trisomy 13, resulting in more babies living longer.