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STAR
steroidogenic acute regulatory protein
STAR is located on the short (p) arm of chromosome 8, at band 8p11.23. Arm ratio per GRCh38 - banding schematic.
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Clinical tests that include this
Overview
The STAR gene encodes the steroidogenic acute regulatory protein, a key regulator in the production of steroid hormones. These hormones include cortisol, aldosterone, and sex hormones such as testosterone and oestrogen, all of which are synthesised from cholesterol within specialised cells in the adrenal glands and reproductive organs.
The STAR protein facilitates the rate-limiting step in this process by enabling cholesterol to move from the outer to the inner mitochondrial membrane, where steroid synthesis begins. Without functional STAR protein, cells cannot efficiently produce steroid hormones, leading to potential hormonal imbalances that can affect development, metabolism, and reproductive function.
What the gene does
The steroidogenic acute regulatory protein functions primarily in steroidogenic tissues, including the adrenal cortex, ovaries, and testes. Its essential role is to transport cholesterol across the aqueous space between the outer and inner mitochondrial membranes, a process that represents the rate-limiting step in steroid hormone biosynthesis.
The protein achieves this by interacting with the outer mitochondrial membrane and facilitating cholesterol transfer to cytochrome P450 side-chain cleavage enzyme (CYP11A1) located on the inner membrane. This enzyme then initiates the conversion of cholesterol to pregnenolone, the precursor for all steroid hormones. The activity of STAR is rapidly induced by trophic hormones such as adrenocorticotropic hormone (ACTH) in the adrenal glands and luteinising hormone (LH) in the gonads, allowing cells to respond quickly to physiological demands for steroid production.
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Chromosome location
STAR is located on the short arm of chromosome 8 at position 11.23, designated as 8p11.23. This chromosomal region contains genes involved in various cellular regulatory processes. The precise exon structure and transcript variants for STAR have been characterised, though the total number of exons varies depending on the specific isoform expressed in different tissues.
Protein structure
Domain architecture has not been experimentally characterised in detail for this protein.
Key variants
Genetic variants in STAR can affect the protein's ability to transport cholesterol across mitochondrial membranes. Pathogenic variants typically result in reduced or absent protein function, impairing steroid hormone synthesis. The clinical consequences of such variants depend on the degree of residual protein activity and can range from mild hormonal disturbances to severe deficiency states affecting multiple steroid-dependent processes.
No pathogenic or likely-pathogenic ClinVar variants recorded yet for this gene.
Associated conditions
Variants in STAR are associated with conditions affecting steroid hormone production. The most significant clinical manifestation occurs when both copies of the gene carry pathogenic variants, leading to impaired synthesis of cortisol, aldosterone, and sex steroids. Such deficiencies can affect adrenal function, salt balance, blood pressure regulation, and sexual development. The severity and specific features depend on the nature of the genetic variants and the degree to which they compromise protein function.
No disease links recorded for this gene in our reference set.
UK clinical status
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Frequently asked questions
What does the STAR protein do?
The STAR protein transports cholesterol into mitochondria, enabling cells in the adrenal glands and reproductive organs to produce steroid hormones such as cortisol, aldosterone, testosterone, and oestrogen.
Where in the body is STAR active?
STAR is predominantly active in steroidogenic tissues, including the adrenal cortex, ovaries, and testes. These are the primary sites where steroid hormones are synthesised from cholesterol.
How do STAR variants affect health?
Pathogenic variants in STAR impair cholesterol transport, reducing the production of steroid hormones. The health impact depends on which hormones are affected and can include adrenal insufficiency, electrolyte imbalances, and disorders of sexual development.