NR0B1

The NR0B1 gene provides instructions for making a protein called DAX1. This protein plays an important role in the development and function of several hormone-producing (endocrine) tissues in the body. These tissues include the small glands located on top of each kidney (the adrenal glands), two hormone-secreting glands in the brain (the hypothalamus and pituitary), and the gonads (ovaries in females and testes in males). Before birth, the DAX1 protein helps regulate genes that direct the formation of these tissues. DAX1 also helps regulate hormone production in endocrine tissues after they have been formed.

Swyer syndrome - caused by mutations in the NR0B1 gene

Changes affecting the NR0B1 gene have been identified in a small number of people with Swyer syndrome, also known as 46,XY complete or pure gonadal dysgenesis.

People normally have 46 chromosomes in each cell. Two of the 46 chromosomes, known as X and Y, are called sex chromosomes because they help determine whether a person will develop male or female sex characteristics. Females typically have two X chromosomes (46,XX), and males ordinarily have one X chromosome and one Y chromosome (46,XY).

A duplication of a region in the X chromosome can result in an extra copy of the NR0B1 gene, which leads to the production of extra DAX1 protein. Another mutation, which may also increase the amount of DAX1 protein that is produced, deletes a segment of DNA near the NR0B1 gene and probably disrupts the normal regulation of the gene. Before birth, an excess of DAX1 protein impairs the process of male sexual differentiation, causing affected individuals to develop a female appearance despite having the chromosome pattern typical of males.

X-linked adrenal hypoplasia congenita - caused by mutations in the NR0B1 gene

More than 110 NR0B1 mutations that cause X-linked adrenal hypoplasia congenita have been identified. Some of these genetic changes are deletions of all or part of the NR0B1 gene. Other mutations lead to the production of an abnormally short version of the DAX1 protein. Still other mutations change single protein building blocks (amino acids) in a critical region of DAX1.

Most of the mutations responsible for X-linked adrenal hypoplasia congenita prevent the NR0B1 gene from producing any active DAX1 protein. A shortage of DAX1 disrupts the normal development and function of hormone-producing tissues in the body. The main characteristics of this condition result when endocrine glands such as the adrenals, hypothalamus, pituitary, and gonads do not produce the right amounts of specific hormones.

other disorders - caused by mutations in the NR0B1 gene

In some cases, genetic material is deleted from a region of the X chromosome that contains several genes, including NR0B1. This deletion results in a condition called adrenal hypoplasia congenita with complex glycerol kinase deficiency. In addition to the signs and symptoms of adrenal hypoplasia congenita, individuals with this condition may have delayed development and problems regulating their blood sugar levels. In rare cases, the deletion also includes the gene associated with Duchenne muscular dystrophy. People with this larger deletion have progressive muscle weakness and wasting in addition to the other features of adrenal hypoplasia congenita with complex glycerol kinase deficiency.