Some forms of Congenital Hyperinsulinism are inherited in an Autosomal Recessive Inheritance pattern. In this case each parent carries one abnormal gene. The disorder only becomes apparent when both copies of the gene are abnormal. In order for an individual to have two abnormal copies of a gene, an abnormal copy of the gene must be inherited from both parents. See diagram.

Even though both parents are carrying one abnormal gene they are usually healthy. Couples who have had a child affected with a recessive disorder (or who are both known to be carriers of a recessive gene by some type of testing) have a 25% chance that any future child will have the disorder, a 25% chance that the child will inherit both normal copies of the gene, and a 50% chance that the child will inherit a normal copy of the gene from one parent, and an abnormal copy of the gene from the other (will be a carrier).

Autosomal Dominant Inheritance

Other forms of Congenital Hyperinsulinism are inherited in an Autosomal Dominant pattern. The abnormal gene that is inherited overrides the normal gene in the pair. Males and females equally transmit this type of disorder. Only one of the parents has to have the affected gene to pass it on to the offspring, and the offspring then has a 50% chance of inheriting the gene and thus the disorder. The same risk applies to each conception, regardless of the outcome of previous conceptions.

A dominant disorder sometimes appears in an individual whose parents do not have the disorder. This occurs when a new mutation has arisen in a gene. In other words, the alteration occurred for the first time in the sperm or egg that resulted in the conception of the child, rather than being inherited from one of the parents. Dominant disorders can be very variable in the clinical presentation.