Inheritance of Genetic Disorders
All of the diseases included in InheriGen are inherited disorders caused by changes, or mutations, in a gene. Genes are found in the cells of the body and are instructions controlling how our bodies develop and function. Mutations in these genes cause disease.
Autosomal Recessive Inheritance
The majority of the disorders on the InheriGen panel are inherited in an autosomal recessive manner.
Individuals inherit half of their genes from each parent. Autosomal recessive disorders occur when parents are carriers for a disorder and a child inherits an altered, or mutated, copy of the gene from each parent. A carrier for an autosomal recessive condition has one normal working copy of the gene while the second copy has a mutation. A carrier is typically unaffected since the working copy of the gene is able to compensate for the copy with the mutation. If both parents are carriers for the same autosomal recessive condition, there is a 25% chance to have a child with that disorder, a 50% chance to have a child who is a carrier and a 25% chance to have a child who is not a carrier and is unaffected. This likelihood is based on whether each parent passes on a normal gene or a gene with a mutation to a child.
X-Linked Recessive Inheritance
Some of the disorders on the InheriGen panel are inherited in an X-linked manner.
X-linked conditions occur because of mutations on the X chromosome. Chromosomes are structures that carry all the genes. Females have two X chromosomes and males have one X and one Y chromosome.
If a male has a mutation in a gene on the X chromosome, he will be affected with the disorder since he lacks a second X chromosome and does not have a second normal copy of the gene. A woman who has a mutation in a gene on an X chromosome is most often an unaffected carrier. For some X-linked disorders, a female may exhibit symptoms of the disorder. Although it is possible for symptoms to be significant, the features are typically less severe compared to symptoms seen in an affected male.
If a woman is a carrier for an X-linked condition, there is a 50% chance that she can pass the normal copy of the gene to a child, and a 50% chance she can pass down the mutation to a child. If a son inherits a mutation on the X chromosome, he will be affected by the condition. If a daughter inherits the same mutation in the gene as her mother, she can be a carrier like her mother. In some situations, a daughter may exhibit symptoms.