Endocrine

Multiple endocrine neoplasia is a group of disorders that affect the body’s network of hormone-producing glands called the endocrine system. Hormones are chemical messengers that travel through the bloodstream and regulate the function of cells and tissues throughout the body.

Multiple endocrine neoplasia type 1 affects about 1 in 30,000 people; multiple endocrine neoplasia type 2 affects an estimated 1 in 35,000 people. Among the subtypes of type 2, type 2A is the most common form, followed by FMTC. Type 2B is relatively uncommon, accounting for about 5 percent of all cases of type 2. 

Mutations in the MEN1, RET, and CDKN1B genes can cause multiple endocrine neoplasia.

Mutations in the MEN1 gene cause multiple endocrine neoplasia type 1.

Multiple endocrine neoplasia type 1 usually has an autosomal dominant pattern of inheritance. People with this condition are born with one mutated copy of the MEN1 gene in each cell. In most cases, the altered gene is inherited from an affected parent. The remaining cases are a result of new mutations in the MEN1 gene and occur in people with no history of the disorder in their family.

Carney complex is a disorder characterized by an increased risk of several types of tumors. Affected individuals also usually have changes in skin coloring (pigmentation). Signs and symptoms of this condition commonly begin in the teens or early adulthood.

People with Carney complex may also develop tumors of other endocrine tissues, including the thyroid, testes, and ovaries. A tumor called an adenoma may form in the pituitary gland, which is located at the base of the brain.

Carney complex is a rare disorder; fewer than 750 affected individuals have been identified.

Mutations in the PRKAR1A gene cause most cases of Carney complex. This gene provides instructions for making one part (subunit) of an enzyme called protein kinase A, which promotes cell growth and division (proliferation). The subunit produced from the PRKAR1A gene, called type 1 alpha, helps control whether protein kinase A is turned on or off.

Carney complex is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. In approximately 80 percent of cases, an affected person inherits the mutation from one affected parent. The remaining cases result from new mutations in the gene and occur in people with no history of Carney complex in their family.

Permanent neonatal diabetes mellitus is a type of diabetes that first appears within the first 6 months of life and persists throughout the lifespan. This form of diabetes is characterized by high blood sugar levels (hyperglycemia) resulting from a shortage of the hormone insulin. Insulin controls how much glucose (a type of sugar) is passed from the blood into cells for conversion to energy.

About 1 in 400,000 infants are diagnosed with diabetes mellitus in the first few months of life. However, in about half of these babies the condition is transient and goes away on its own by age 18 months. The remainder are considered to have permanent neonatal diabetes mellitus.

Permanent neonatal diabetes mellitus may be caused by mutations in several genes.

About 30 percent of individuals with permanent neonatal diabetes mellitus have mutations in the KCNJ11 gene. An additional 20 percent of people with permanent neonatal diabetes mellitus have mutations in the ABCC8 gene. 

Mutations in the KCNJ11 or ABCC8 gene that cause permanent neonatal diabetes mellitus result in K-ATP channels that do not close, leading to reduced insulin secretion from beta cells and impaired blood sugar control.

Permanent neonatal diabetes mellitus can have different inheritance patterns. When this condition is caused by mutations in the KCNJ11 or INS gene it is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. In about 90 percent of these cases, the condition results from new mutations in the gene and occurs in people with no history of the disorder in their family. In the remaining cases, an affected person inherits the mutation from one affected parent.