Genetics of Alstrom Syndrome

Alstrom Syndrome is a genetic disorder that is termed 'autosomal recessive'.   It is caused by alterations (or mutations) in the gene ALMS1 that cause it not to function properly.  It is inherited by both males and females with equal probability.

Almost all of our genes come in pairs, one inherited from each of our parents. Most parents are not aware that they carry an alteration in ALMS1 gene until the birth of an affected child.  A carrier of Alstrom Syndrome has one copy of the altered or mutated gene.   So each parent of an affected child carries only one copy of the gene and unknowingly passes it to their offspring. A recessive condition like Alstrom Syndrome results when a child inherits two copies of the altered ALMS1, one from each parent. Both parents must be carriers in order for any of their children to be affected.  In the case of Alström Syndrome, there are no visible symptoms of the disorder in an individual who carries only one altered copy of ALMS1. The only consequence of being a carrier is the possibility of transmitting Alstrom Syndrome to a child.

Couples in which the man and the woman are each carriers of an alteration in ALMS1, have a 25% chance with each pregnancy of conceiving a child with Alstrom Syndrome. There is a 50% chance of producing a child who is a carrier like the parents and a 25% chance that the child will be neither a carrier nor affected. These numbers are illustrated in the following chart: