The Health Blog

GENETIC DISORDERS AND GENETIC COUNSELLING: GENETIC DISORDERS

Genetic disorders are defects caused by faulty genes or chromosomes, many of which are hereditary, that is, passed on to the baby via the parents. Approximately 1% of children are born with a significant congenital abnormality. There are certain well recognised conditions in which abnormalities in chromosomes are known to cause specific syndromes or diseases — an example of this is Down syndrome. Inherited disorders are caused by abnormal genes or chromosomes, and are passed on to the child by one or both parents, depending on whether the specific disorder is caused by a dominant or recessive gene. Abnormal genes can also be carried on the sex chromosomes. This is why some conditions only occur in, or are passed on by, one sex. Over 1500 rare diseases are caused by the expression of one faulty dominant gene. For a recessive gene to receive expression it has to be present in both parents.

Environmental factors also play a part in causing changes or mutations to the genetic make-up of a foetus. Many drugs taken during the first twelve weeks of pregnancy can cause congenital abnormalities, as can irradiation. Certain illnesses in the mother at the time of pregnancy, such as diabetes, if not well controlled, are associated with a higher rate of certain genetic defects in the baby.

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