Hereditary nonspherocytic hemolytic anemias are inherited disorders, meaning they are caused by a harmful change (mutation) in a specific gene. Many different genes can cause different types of hereditary anemia. The specific gene involved determines the exact type of anemia a person has, and how it is inherited. A mutation can cause a gene to not work properly, meaning the person’s body does not produce enough of related protein. In some anemias, this leads to a fragile membrane, or outer layer, of the red blood cells, causing the cells to die more quickly. In other types of anemia, the gene change causes a problem with the way red blood cells get the energy they need to function properly. Some people with a non-working gene only have symptoms of hereditary nonsphyrocytic hemolytic anemia after a trigger, such as an illness, taking a certain medication or eating specific foods.
Some forms of hereditary nonsphyrocytic hemolytic anemia are inherited as recessive disorders. Recessive genetic disorders occur when a person inherits a non-working gene from each parent. If a person receives one working gene and one non-working gene for the disease, the person will be a carrier for the disease, but usually will not show symptoms. The chance for two carrier parents to both pass on the non-working gene and, therefore, have an affected child is 25% with each pregnancy. The risk to have a child who is a carrier, like the parents, is 50% with each pregnancy. The chance for a child to receive working genes from both parents is 25%. The risk is the same for males and females.
Other types of anemia are inherited as dominant conditions. Dominant genetic conditions occur when only a single copy of a non-working gene is necessary to cause a particular disease. The non-working gene can be inherited from either parent or can be the result of a new gene change in that person. The risk of passing the non-working gene from an affected parent to an offspring is 50% for each pregnancy. The risk is the same for males and females.
There are some types of hereditary nonspherocytic hemolytic anemia that are X-linked disorders. X-linked genetic disorders are conditions caused by a non-working gene on the X chromosome and manifest mostly in males. Females that have a non-working gene present on one of their X chromosomes are carriers for that disorder. Carrier females usually do not display symptoms because females have two X chromosomes and only one carries the non-working gene. Males have only one X chromosome that is inherited from their mother, and a Y chromosome that is inherited from their father. If a male inherits an X chromosome that contains a non-working gene he will develop the disease. Female carriers of an X-linked disorder have a 25% chance with each pregnancy to have a carrier daughter like themselves, a 25% chance to have a non-carrier daughter, a 25% chance to have a son affected with the disease and a 25% chance to have an unaffected son. If a male with an X-linked disorder is able to reproduce, he will pass the non-working gene to all of his daughters who will be carriers. A male cannot pass an X-linked gene to his sons because males always pass their Y chromosome instead of their X chromosome to male offspring.