Some cases of the carney complex occur due to mutations of the PRKAR1A gene. This mutation may occur randomly for no apparent reason (i.e., new mutation) with no family history or be inherited as an autosomal dominant trait. The majority of cases of Carney complex have occurred in individuals with a family history of the disorder.
Genetic diseases are determined by the combination of abnormal genes for a particular trait that are on the chromosomes received from the father and the mother. Dominant genetic disorders occur when only a single copy of an abnormal gene is necessary for the appearance of the disease. The abnormal gene can be inherited from either parent, or can be the result of a new mutation (gene change) in the affected individual. The risk of passing the abnormal gene from affected parent to offspring is 50 percent for each pregnancy regardless of the sex of the resulting child.
Some individuals with the Carney complex do not have an identifiable mutation of the PRKAR1A gene. Researchers believe that additional, as yet unidentified, genes may cause the disorder in these cases (genetic heterogeneity). Investigators have determined that an as yet unidentified gene on the short arm (p) of chromosome 2 is involved in some cases of Carney complex. These cases are sometimes referred to as Carney complex type II. More research is necessary to determine the gene on this region of chromosome 2 that causes certain cases of Carney complex.
Investigators have determined that the PRKAR1A gene is located on the long arm (q) of chromosome 17 (17q22-q24). Chromosomes, which are present in the nucleus of human cells, carry the genetic information for each individual. Human body cells normally have 46 chromosomes. Pairs of human chromosomes are numbered from 1 through 22 and the sex chromosomes are designated X and Y. Males have one X and one Y chromosome and females have two X chromosomes. Each chromosome has a short arm designated “p” and a long arm designated “q”. Chromosomes are further subdivided into many bands that are numbered. For example, “chromosome 11p13” refers to band 13 on the short arm of chromosome 11. The numbered bands specify the location of the thousands of genes that are present on each chromosome.
The PRKAR1A gene is believed to be a tumor suppressor gene. A tumor suppressor is a gene that slows down cell division, repairs damage to the DNA of cells, and tells cells when to die, a normal process called apoptosis. The PRKAR1A gene creates (encodes) a protein known as protein kinase A (PKA) R1alpha regulatory subunit. A mutation of the PRKAR1A gene leads to increased PKA signaling in affected tissues. It is believed that PKA can suppress or stimulate cell growth and proliferation. However, the exact function of this protein and how mutations of the PRKAR1A gene ultimately lead to the symptoms of Carney complex are not fully understood.
The Carney complex affects males and females in equal numbers. Approximately 600 affected individuals have been reported since the disorder was first described in the medical literature in 1985. The disorder can present at any age, but the mean age at diagnosis is 20.
The Carney complex is rare. Several hundred cases have been reported worldwide. It is estimated that between 60% and 75% of cases of Carney complex run in families. The remaining 25% to 40% of cases appear to be sporadic and may be due to a de novo, meaning new gene mutation.