Autosomal recessive genetic diseases are usually inherited from both parents, who are both genetic carriers. However, rare cases of sporadic genetic disease can also occur. See also details of inheritance patterns in Inheritance of Autosomal Recessive Genetic Diseases.
Inheritance properties of Autosomal Recessive Genetic Diseases: Disease inherited from: Typically autosomal recessive diseases are inherited from both parents who are unknowingly genetic carriers. Autosomal recessive diseases are relatively rare, because to get the disease a person must inherit a bad gene from each parent, not just one bad gene. So both parents must have a bad gene. However, parents can be genetic carriers of the autosomal recessive disease, since they typically only have one bad gene themselves.
Gender bias in inheritance: Male or females get the disease equally, because an autosomal error is unrelated to the sex chromosomes, and males and females have equal numbers of autosomes.
Inheritance odds for Autosomal Recessive Genetic Diseases: Overall odds of inheritance: Typically autosomal recessive diseases are inherited from both parents who are unknowingly genetic carriers. Autosomal recessive diseases are relatively rare, because to get the disease a person must inherit a bad gene from each parent, not just one bad gene. So both parents must have a bad gene. However, parents can be genetic carriers of the autosomal recessive disease, since they typically only have one bad gene themselves.
Sibling of diseased child odds of inheriting disease: 25% usually. If parents have one affected child, the odds of a second are usually 25%. If parents have a child with the disease, this almost always means that they are both carriers. The chances a second child will also have the disease are the same as for two parent carriers: 25% chance of disease, 50% chance the second child is a carrier, and 25% chance of neither disease nor carrier. Note that genetic testing can often detect the rarer case where a child gets a sporadic genetic disease without both parents being carriers (perhaps only one is a carrier and the child had one genetic mutation, coincidentally mutating exactly the same gene as in the carrier parent).
Inheritance from one diseased parent odds: Usually 0% of disease, 100% of being a genetic carrier. Surprisingly, children of a person with an autosomal recessive disease person will typically not have the disease but the odds are 100% the child will be a carrier. The affected parent has two bad copies of the gene, so the child gets a bad gene from that parent, but usually a good second copy from the other unaffected parent. In the rare case that a person with an autosomal recessive diseases marries someone who is also affected or a carrier of exactly the same autosomal recessive disease, then the odds of actually getting the disease in the child are higher. If one parent has the autosomal recessive disease, and the other parent is a carrier of the same autosomal recessive disease, a child has a 50% chance of getting the autosomal recessive disease, and 50% chance of being a carrier. The child definitely gets one bad gene from the diseased parent, and has a 50% chance of getting a second one from the carrier parent.
Inheritance from two diseased parents odds: 100%. In the uncommon case where two people who have an autosomal recessive disease (i.e. not just carriers), there are 4 copies of bad genes, and no good genes in the parents, so the child will get the autosomal recessive disease. This is rare, but can occur, for example, if two people with the same autosomal recessive disease meet at a disease support group or otherwise.
Genetic carriers of Autosomal Recessive Genetic Diseases: Inheritance from one carrier parent odds: 0% approximately. Both parents must be genetic carriers of an autosomal recessive disease for a child to get the disease, except the rare case of a sporadic mutation. If only one parent is a carrier (and the other unaffected), the child cannot get an autsomal recessive disease, but might still be a carrier (typically 50% chance of being a genetic carrier of the autosomal recessive disease).
Inheritance from two carrier parents odds: 25% chance of disease, 50% chance the child is a carrier, and 25% chance of neither disease nor carrier. If both parents are a carrier of an autosomal recessive disease, there is a 25% chance that their child will have the disease. There is also a 50% chance the child will be a carrier, and only 25% chance the child will be neither diseased nor carrier. The situation where both parents are carriers is the most likely way that children with an autosomal recessive disease are born.
Inheritance features for Autosomal Recessive Genetic Diseases: Inheritance pattern: Inheritance patterns for autosomal recessive diseases tend to be "horizontal", with a generation being affected (i.e. many siblings of the same parents), but not their parents nor their own children. Parents and next-generation children will usually be carriers.
Sporadic form of disease possible?: Extremely unlikely. Theoretically can occur from a double mutation even if neither parent is a carrier, or from a single mutation if one parent is a carrier.
Double dominant form of disease possible?: The term "double dominant" does not really apply to recessive diseases.
Inheritance of Autosomal Recessive Genetic Diseases refers to whether the condition is inherited from your parents or "runs" in families. The level of inheritance of a condition depends on how important genetics are to the disease. Strongly genetic diseases are usually inherited, partially genetic diseases are sometimes inherited, and non-genetic diseases are not inherited. For general information, see Introduction to Genetics.
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