This type of inheritance requires the presence of a pathogenic variant in both copies of the gene for a person to have the genetic disease. Both parents must be carriers of a pathogenic variant in the gene in order to be at risk to have an affected child. The child must inherit a pathogenic variant from each carrier parent in order to be affected. There is a 1 in 4 chance that a baby will inherit two pathogenic variants of the gene and be affected when both parents are carriers.


An individual who has only one pathogenic variant in a gene that causes disease in an autosomal recessive or X-linked recessive inheritance pattern. Most carriers do not show symptoms of the disease associated with pathogenic variants in this gene. However, a carrier is at an increased risk to have a child affected with the disease for which they are known to be a carrier.


A chromosome is an organized package of DNA that is found in most of the cells in our bodies. Humans have 23 pairs of chromosomes, one of each pair is inherited from our mother and the other is inherited from our father.

DNA (deoxyribonucleic acid)

DNA is the chemical name for the molecule that is in all of the cells in our body that carry the genetic instructions, or blue print, for how the body grows, develops and functions. These building blocks allow for the transmission of genetic information from one generation to the next.


A gene is the unit of DNA on a chromosome that codes for a specific hereditary trait. Each gene contains a particular set of instructions, usually related to a particular function in the body and determines some characteristics. Most genes come in pairs. One member of each gene pair comes from the mother and the other comes from the father. Depending on how the gene pair interacts, some genes are dominant and other genes are recessive (see autosomal inheritance).


The manner in which a gene or trait is passed on in a family.


A pathogenic variant is a change in the DNA that negatively affects the gene’s ability to function properly.


This type of inheritance requires the presence of a pathogenic variant in a gene located on the X-chromosome. When the pathogenic variant is inherited from the unaffected carrier mother, the male child will have the genetic disease.

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