A gene on one of the first 22 pairs of chromosomes, which, when present in two copies, causes a trait or disease to be expressed.
Autosomal recessive inheritance means that the gene carrying the mutation is located on one of the autosomes (chromosome pairs 1 through 22). This means that males and females are equally affected. “Recessive” means that both copies of the gene must have a mutation in order for a person to have the trait. One copy of the mutation is inherited from the mother, and one from the father. A person who has only one recessive gene mutation is said to be a “carrier” for the trait or disease, but he/she does not have any health problems from carrying this one mutation. Most people do not know they carry a recessive gene mutation for a disease until they have a child with the disease. Once parents have had a child with a recessive disease, there is a one out of four, or 25 percent chance, with each subsequent pregnancy, for another child to be born with the same disorder. This means that there is a three out of four, or 75 percent chance, for another child to not have the disease:
The birth of a child with a recessive condition is often a total surprise to a family, since in most cases, there is no previous family history of the condition. Many autosomal recessive conditions occur this way. It is estimated that all people carry about 20 recessive genes that cause genetic diseases or conditions. It is only when a person has a child with a partner that carries the same recessive gene mutation, that there is a chance of having a child with a recessive disorder. Mutations in certain genes have occurred over time in different parts of the world. Virtually anyone can carry a mutation in any one of the recessive genes; however, there may be certain ethnic groups more likely to carry certain recessive gene mutations, because of where the mutation originated.