Is Severe combined immunodeficiency inherited ?
How is severe combined immunodeficiency inherited? Severe combined immunodeficiency (SCID) can be inherited in an X-linked recessive or autosomal recessive manner depending on the genetic cause of the condition. X-linked SCID is the most common type of SCID and is inherited in an X-linked recessive manner. A condition is X-linked if the changed (mutated) gene responsible for the condition is located on the X chromosome. The X chromosome is one of the two sex chromosomes; females have two X chromosomes and males have one X chromosome and one Y chromosome. In males, one mutated copy of the responsible gene causes signs and symptoms of the condition because they don't have another X chromosome with a working copy of the gene. In females, having one mutated copy of the gene would make them an unaffected carrier; a mutation would have to occur in both copies of the gene to cause the condition. This is why X-linked recessive disorders, including X-linked SCID, occur much more frequently in males. Because fathers only pass their Y chromosome on to their sons, fathers cannot pass X-linked conditions on to their sons. The other, less common causes of SCID are inherited in an autosomal recessive manner. These types are due to mutations in responsible genes on other chromosomes (not the sex chromosomes). In autosomal recessive conditions, a person must have mutations in both copies of the responsible gene in order to have signs or symptoms of the condition. In most cases, the affected person inherits one mutated copy of the gene from each of the parents, who are typically unaffected carriers.