Metabolic diseases
All about heredity
Metabolic disorders are hereditary diseases. Most metabolic disorders are ‘autosomal recessive’.
Autosomal recessive
Autosomal recessive means that the abnormal gene is located on one of the 22 common chromosomes. Both boys and girls can be affected. Recessive means that two abnormal genes are needed to have the disease. A child with a metabolic disease has inherited one abnormal gene from both parents. The parents themselves are not affected and are often unaware that they are carriers. With each pregnancy, these parents have a 25% chance of having a child with a metabolic disease, which often only appears at birth. They also have a 50% chance of having a child who is not affected, but is a carrier. Children can only pass on the disease if their partner also has the same abnormality in their DNA.
Autosomal dominant
Autosomal means that the abnormal gene is located on one of the 22 common chromosomes. Both boys and girls can be affected. In addition, a single abnormal (dominant) gene is already the cause of the disease. In this case, the normal gene does not sufficiently compensate. In a child with an autosomal dominant disease, one of the parents carries an abnormal dominant gene. This parent also has the disease. A person with an autosomal dominant disease has a 50% chance of having a child with the same disease.
X-linked recessive
Metabolic diseases can also be inherited in a sex-linked recessive manner. This term means that the abnormal gene is located on a sex chromosome, almost always the X chromosome. These diseases occur almost exclusively in boys and men because they only have one X chromosome. If their mother has an abnormal gene on one of her X chromosomes, she is usually not sick herself because her other X chromosome still contains the normal gene. Her sons have a 50/50 chance of inheriting the disease. Her daughters are healthy but have a 50/50 chance of being carriers of the abnormal gene. They can also pass the disease on to their sons. Again, women are often unaware that they are carriers until a son is born with a metabolic disease.
De novo mutation
When patients develop the disease due to a new mutation in the gene, the mutation originated in the patient himself and was therefore not inherited from the parents.
