Genetic screening: ethical issues - Nuffield Council on Bioethics

Diseases
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Only those diseases mentioned in the text are included here. The intention is simply
to give a very brief description of the main features and mode of inheritance. For many
conditions variations occur and it must be emphasised that no attempt has been made
to give a comprehensive account of these.
Adrenoleukodystrophy (ALD)
Mode of inheritance : X-linked
Adrenoleukodystrophy is a very rare inherited disorder affecting boys who normally
develop failure of their adrenal glands (producing the hormone cortisol), fits, and
deterioration of brain function. For reasons that are not understood, some males (a
minority) escape the problems with the central nervous system but may develop
Addison’s disease in adulthood (see, for example, Chapter 5, Fig E). There is no
known cure or satisfactory treatment and death usually occurs in childhood. The
disease is inherited through the mother who carries the defective gene on one of her
X chromosomes. The risk for boys inheriting the disease is 1 in 2; 1 in 2 girls will be
carriers, like their mother.
Alpha-1-antitrypsin deficiency
Mode of inheritance : recessive
The commonest form of alpha-1-antitrypsin deficiency occurs in about 1 in 3,000 people
who inherit an abnormal gene from each parent. Almost all those who smoke will
develop progressive lung disease (emphysema) in adult life. In non-smokers,
emphysema occurs later or may never develop. About 20% of infants with the disease
develop jaundice and some of these may develop liver damage. Carriers with only one
abnormal gene usually have no problems but may possibly have an increased risk of
emphysema if they smoke heavily.
Breast cancer
It is believed that several genes play a role in the 25,000 new cases of breast cancer
diagnosed in Britain every year, particularly where onset is early or where multiple
family members are affected. A gene that predisposes women in some families to
breast cancer has been traced to a region of chromosome 17 and it is likely that the
gene itself will soon be isolated.
Congenital disorders
Disorders which are present at birth, not necessarily hereditary. For example the limb
deformities caused by the drug thalidomide, or the malformations caused by maternal
rubella (German measles), are congenital but not inherited, whereas other forms of
malformation may be hereditary.