HSD17B10

The HSD17B10 gene provides instructions for making an enzyme called HSD10, which is found in many areas of the body. The HSD10 enzyme is located within mitochondria, the energy-producing centers inside cells, where it has several different functions.

The HSD10 enzyme plays an important role in processing steroid hormones and fats. This enzyme also helps break down the protein building block (amino acid) isoleucine. Specifically, it is responsible for the fifth step in this process, in which 2-methyl-3-hydroxybutyryl-CoA is converted into 2-methylacetoacetyl-CoA. Through a similar method, the HSD10 enzyme processes a group of fats called branched-chain fatty acids.

This enzyme is also necessary for several chemical reactions involving female sex hormones (estrogens) and male sex hormones (androgens). HSD10 inactivates a potent form of estrogen called 17β-estradiol by converting it to a weaker form called estrone. This enzyme also generates a potent androgen called dihydrotestosterone from a weak androgen called 3α-androstanediol. The HSD10 enzyme is essential for maintaining appropriate levels of male and female sex hormones.

The HSD10 enzyme is needed for certain chemical reactions involving neurosteroids, which are substances that regulate the activity of the nervous system. This enzyme inactivates two neurosteroids called allopregnanolone and allotetrahydrodeoxycorticosterone. These neurosteroids interact with receptors that prevent the brain from being overloaded with too many signals. By regulating the activity of these neurosteroids, the HSD10 enzyme helps maintain normal brain function.

17β-hydroxysteroid dehydrogenase type 10 deficiency - caused by mutations in the HSD17B10 gene

At least six mutations in the HSD17B10 gene have been found to cause 17β-hydroxysteroid dehydrogenase type 10 (HSD10) deficiency. These mutations change single amino acids in HSD10, which reduces or eliminates the activity of the enzyme. One mutation, which has been found in multiple unrelated individuals, replaces the amino acid arginine with the amino acid cysteine at position 130 in the enzyme (written as Arg130Cys or R130C). This mutation results in a nonfunctional enzyme that is quickly broken down by the cell. It remains unclear how a shortage (deficiency) of the HSD10 enzyme leads to the signs and symptoms of this disorder. Some researchers suspect that the neurological problems associated with HSD10 deficiency are caused by abnormal neurosteroid activity. Other features of the disorder may be related to the inability to process isoleucine and certain fats.

other disorders - caused by mutations in the HSD17B10 gene

One specific mutation in the HSD17B10 gene causes a form of X-linked intellectual disability called MRXS10. This disorder is characterized by intellectual disability, uncontrollable movements of the limbs (choreoathetosis), and abnormal behavior. The mutation replaces the DNA building block (nucleotide) cysteine with the nucleotide adenine at position 605 in the HSD17B10 gene (written as 605C>A). Although this mutation does not change the sequence of amino acids that makes up the HSD10 enzyme, it can disrupt how information in the gene is spliced together to make a blueprint for producing the enzyme. As a result, there is reduced production of the HSD10 enzyme. It remains unclear how the shortage of HSD10 results in the signs and symptoms of MRXS10.

At least 22 individuals with intellectual disability have been found to have small duplications of genetic material that include HSD17B10 and various other genes on the X chromosome. The extra copy of the HSD17B10 gene leads to increased production of the HSD10 enzyme, which likely affects neurosteroid regulation. Extra copies of other genes in this region of the X chromosome may also play a role in intellectual disability.