Genetic screening: ethical issues - Nuffield Council on Bioethics

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Hypertrophic cardiomyopathy
Mode of inheritance : dominant
A rare dominantly inherited disorder of the muscle of the heart. It may cause heart
failure in infancy, but problems may not arise until later childhood or adult life. It is the
most common cause of sudden death from heart disease in young people, particularly
athletes.
Neural Tube Defects (NTD)
Mode of inheritance : both genetic and environmental factors involved
These conditions occur if the brain and/or the spinal cord with its protecting skull and
spinal column fail to develop properly. They include anencephaly, where most of the
brain and skull are absent and stillbirth or death soon after delivery is inevitable, and
spina bifida, where the spinal canal is not closed and the spinal cord and nerves may
be damaged. Infants born with spina bifida show a wide range of physical disabilities
and in the most severe forms the legs and bladder may be paralysed. Hydrocephalus
(excess fluid within the brain) is a frequent complication. The causes of NTD are
complex, but there is an undoubted genetic component, the risk for subsequent
offspring after the birth of an affected child being increased about 10 fold. Maternal
diet also plays a part : folic acid has a protective effect.
High levels of a protein called alphafetoprotein (AFP) are found in the amniotic fluid and
maternal blood when the fetus has either anencephaly or spina bifida. In many areas
of the UK, serum AFP estimation is offered routinely to all pregnant women around the
16th week of pregnancy to identify a risk group for neural tube defects; ultrasound
scanning is also used. The incidence of NTD at birth in the UK has fallen from about
4 per 1,000 20 years ago, to about 0.3 per 1,000, partly due to antenatal diagnosis and
selective termination of pregnancy, but also because of a primary decrease in
frequency.
Phenylketonuria (PKU)
Mode of inheritance : recessive
PKU is a rare inherited disorder, affecting about 1 in 10,000 births in the UK. Affected
individuals inherit the abnormal gene from each parent and are unaffected at birth; but,
with the introduction of feeding, a substance in the blood (phenylalanine and 10
breakdown products) builds up and causes brain damage, so that untreated children
become severely mentally handicapped. Every baby in the UK has a blood test for
phenylalanine at about 6 days of age and if the diagnosis is confirmed, a special diet
is started. With rigorous dietary control mental development can be normal, although
the intellectual status of early treated subjects is not as good as was originally thought.
The dietary control has to be continued at least into late childhood and possibly
throughout life. Women with PKU require particularly strict dietary control during
pregnancy. The current <strong>screening</strong> test only detects babies who may be affected.