Many diseases are considered heritable, or able to be passed down from parent to child. However, some diseases have more clear family links than others. One group of disease, which includes cystic fibrosis, spinal muscular atrophy (SMA), and Tay-Sachs, are known as recessive disorders.
The human genome
The human genome contains the blueprints required for a human being. The genome is broken down into 23 different sections known as chromosomes, which contain all of the genetic material that act as the instructions for the body. These instructions are known as genes.
Each person has two copies of each gene: one inherited from their mother, and one from their father. Many disorders, like different cancers or Alzheimer’s, are believed to result from a combination of many different genes interacting with one another. Recessive disorders involve just one gene. If both parents pass on the recessive copy of one of these genes, their child will be affected with the recessive disorder.
Carrier screening identifies risk
Carrier screening is used before conception, or during early pregnancy, to identify carriers of a recessive disorder. A person with two recessive copies of a disease-causing gene will have the disease. People with just one recessive copy won’t have the disease themselves, but may pass it on to their children: they are known as carriers. Carrier screening checks the genes of both parents to see if parents are carriers of recessive, disease-causing genes.
Carrier screening doesn’t diagnose recessive disorders, but it can let you know the risk. For instance, if both parents are carriers of SMA (have one copy of the recessive gene, but do not have the disease), a child will have a 25% chance of inheriting the disease. If only one parent has the recessive gene, children of these parents have a 50% chance of becoming carriers of the disease, but will not have it themselves.
Different recessive disorders are more likely to be found in those of certain ethnic groups.
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