Genetic screening: ethical issues - Nuffield Council on Bioethics

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but to a lesser degree : about one-third of girls carrying this genetic abnormality will
have some degree of learning difficulty.
Severe learning difficulty is the main characteristic of the disorder, although this varies
markedly in severity between individuals. There is no limitation of life expectancy for
children with the fragile X syndrome.
Glucose-6-phosphate dehydrogenase deficiency (G6PD)
Mode of inheritance : X-linked
This red blood cell disorder occurs mainly in males and is particularly common in the
Middle East, China and West Africa. It causes anaemia and jaundice in the newborn
period but usually there are no symptoms after this period unless acute destruction of
the red blood cells (causing anaemia and jaundice) is triggered by some drugs, by
infections, and certain foods such as fava beans - it is sometimes called ‘favism’.
Haemoglobin disorders (haemoglobinopathies)
The haemoglobin disorders are the commonest of all genetic disorders worldwide.
These conditions are caused by a failure of haemoglobin, the substance in red blood
cells which carries oxygen, to be produced normally or to carry oxygen efficiently. The
two most important groups of haemoglobin disorders are sickle cell disease and the
thalassaemias:
Sickle Cell Disease
Mode of inheritance : recessive
An inherited abnormality of the haemoglobin (called haemoglobin S) in the red blood
cells may cause deformity of the cells known as sickling. Those at most risk of
inheriting sickle cell disorders are people of African, African/Asian Caribbean, Eastern
Mediterranean, Asian and Middle Eastern origin. The inheritance of one sickle cell
gene (sickle cell trait) generally causes no problems; individuals who inherit the gene
from each parent have sickle cell disease.
A child born with sickle cell disease does not generally have problems until after the
age of four to six months. After this age most children become anaemic because the
sickle cells are destroyed in the blood. The children may also from time to time get
additional problems such as hand-foot syndrome (swelling of the hands and feet), mild
to excruciating pains throughout the body, chest infections, strokes and damage to
various parts of the body including the hips, shoulders, eyes and lungs. These are due
to the sickle cells causing blockage of smaller blood vessels and other problems. The
majority of affected individuals survive into adulthood but there are occasional deaths
of young children and adults due to complications such as overwhelming infections and
sickling in the spleen and lungs. Haemoglobin C is another haemoglobin variant that
causes similar problems when paired with haemoglobin S. (mentioned in paragraph
6.25)