Adams-Oliver syndrome Health Article

Definition

Adams-Oliver syndrome (AOS) is a condition involving the combination of congenital scalp defects (called aplasia cutis congenita) and a specific type of limb defect.

Description

Adams-Oliver syndrome is a genetic condition characterized by aplasia cutis congenita, most commonly of the scalp and skull, and terminal transverse limb defects. Congenital heart disease has also been reported in individuals with this condition. The exact cause of the condition is not well-understood. There is extreme variability in the severity of problems between families with AOS.

Genetic profile

There have been both familial and non-familial cases of Adams-Oliver syndrome reported. The majority of genetic cases have been inherited in an autosomal dominant manner, but autosomal recessive and sporadic inheritance have also been reported. A difference in the presentation of AOS in the dominant versus recessive form has not been documented.

Autosomal dominant inheritance means that only one abnormal gene copy is required for the disease to occur. For persons with a copy of the gene, the risk of passing it to their offspring is one in two or 50%.

Autosomal recessive inheritance means that two defective gene copies must be inherited, one from each parent, for the disease to manifest itself. Persons with only one gene mutation are carriers for the disorder. Individuals who are a carrier for the recessive type of Adams-Oliver syndrome do not have any symptoms (asymptomatic) and do not know they are a carrier unless they have had a child with the syndrome. Carrier testing is not available since the gene location is not known at this time. The liklihood that each member of a couple would be a carrier for a mutation in the same gene is higher in people who are related (called consanguineous). When both parents are carriers for the recessive type of Adams-Oliver syndrome, there is a one in four chance (25%) in each pregnancy for a child to have the disease. There is a two in three chance that a healthy sibling of an affected child is a carrier.

Sporadic occurrences of AOS may be caused by a dominant gene with variable expressivity (no one else in the family has symptoms, but some are actually gene carriers), a new (dominant) mutation occuring during the formation of the embryo where neither parent is a carrier, or the existence of both genetic and non-genetic causes for the same syndrome.

Different mechanisms have been postulated to explain how Adams-Oliver syndrome occurs. They include trauma, uterine compression, amniotic band sequence (a condition resulting from strands of the amnion membrane causing amputation of parts of the fetus), vascular disruption (blockage of blood flow to a developing part or parts of the fetus), and a large blood clot in the placenta which blocks certain important blood vessels and interrupts blood supply to developing structures. Recently, Adams-Oliver syndrome has been hypothesized to occur as a result of abnormalities in small vessel structures that occur very early in embryo formation. The vascular anomaly could be the result of a genetic defect causing decreased stability of embryonic blood vessels in the presence of specific forces.