Introduction

Testing healthy children to identify genetic conditions has been possible for many years by clinical examination, blood tests and other investigations that recognise the relevant phenotype. Examples include the recognition of children with type I neurofibromatosis by examination of the skin, the biochemical recognition of infant boys with Duchenne muscular dystrophy, the identification of unaffected carriers of haemoglobin disorders (e.g. sickle cell disease) by haematological tests, and the identification of some asymptomatic children or adolescents with autosomal dominant polycystic kidney disease by ultrasound examination of the kidneys.

The recent development of molecular genetic technologies has transformed the situation by greatly extending the possibilities for genetic testing. Molecular genetic methods test directly for the relevant gene. These tests can be carried out at any stage of life from conception onwards, using any nucleated tissue, for example white blood cells or a mouthwash sample of oral epithelial cells. There is usually no need to test a tissue affected by the disease process. Many genetic tests are now available for inherited diseases for which there had previously been no diagnostic test. Such tests can identify children who are likely to develop genetic disorders in adult life, and can also identify those carrying recessive disease genes, which have no effect on the health of carriers but may have implications for the health of carriers' future children.

This chapter addresses controversial issues raised by the possibility of testing children that are (apparently) healthy (Harper and Clarke, 1990).