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NSDHL
NAD(P) dependent 3-beta-hydroxysteroid dehydrogenase NSDHL
The NSDHL gene provides instructions for an enzyme crucial in cholesterol synthesis, with variants linked to conditions such as CHILD syndrome. The NSDHL gene is responsible for producing an enzyme that plays a key role in the body's cholesterol production pathway.
NSDHL is located on the long (q) arm of chromosome X, at band Xq28. Arm ratio per GRCh38 - banding schematic.
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Overview
The NSDHL gene encodes a protein that functions as an NAD(P)-dependent 3-beta-hydroxysteroid dehydrogenase, an enzyme essential for cholesterol biosynthesis within the body. Cholesterol is a vital lipid required for numerous biological processes, including cell membrane formation, hormone production, and the synthesis of bile acids important for digestion. The NSDHL enzyme facilitates a specific step in the conversion of lanosterol to cholesterol, involving the precise removal of a methyl group. Disruptions in this intricate process due to NSDHL gene variants can have significant health implications, notably manifesting in conditions like CHILD syndrome.
While often associated with cardiovascular health when present in high levels, cholesterol is indispensable for foetal development, influencing the normal formation of the brain, limbs, and genital tract. Its role extends to insulating nerve cells as a component of myelin, underscoring its broad importance in human physiology.
What the gene does
The NSDHL gene provides instructions for an enzyme that plays a critical role in the cholesterol synthesis pathway. Specifically, this enzyme is an NAD(P) dependent 3-beta-hydroxysteroid dehydrogenase. Its primary function involves a crucial step in converting lanosterol, a precursor molecule, into cholesterol. This conversion process is complex and involves multiple enzymatic reactions.
The NSDHL enzyme participates in an enzyme complex that is responsible for removing a carbon atom and three hydrogen atoms (a methyl group) from the lanosterol molecule. This precise modification is necessary for the progression of cholesterol synthesis. Cholesterol itself is a fundamental lipid, not only absorbed from dietary sources but also synthesised by the body, fulfilling diverse biological roles. It is an integral component of cell membranes, contributes to the myelin sheath that insulates nerve cells, and acts as a precursor for various hormones and bile acids. Furthermore, during embryonic development, cholesterol critically interacts with signalling proteins to guide the formation of the brain, limbs, and genital tract. Therefore, proper functioning of the NSDHL enzyme is vital for maintaining appropriate cholesterol levels and its associated developmental and physiological processes.
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Chromosome location
The NSDHL gene is situated on the long arm of the X chromosome at position Xq28. This chromosomal location is significant because it defines the gene's inheritance pattern as X-linked. The gene provides instructions for a protein that is 373 amino acids in length.
Protein structure
The NSDHL protein is composed of 373 amino acids. A notable feature of its structure is a specific motif located at amino acid positions 370-373. This motif is responsible for preventing the protein's secretion from the endoplasmic reticulum (ER), indicating its role in retaining the NSDHL enzyme within this cellular compartment where cholesterol synthesis primarily occurs.
Key variants
Variants within the NSDHL gene can alter the genetic instructions for producing the NSDHL enzyme, potentially affecting its structure or function. Many identified variants involve changes to single protein building blocks, called amino acids, within the enzyme. These changes can lead to an enzyme that is less efficient, non-functional, or improperly localised, thereby disrupting the critical process of cholesterol synthesis. The specific impact of a variant often depends on its location within the gene and the nature of the amino acid change.
Sample of pathogenic variants
10 pathogenic / likely-pathogenic variants from ClinVar, ranked by review status (expert-panel-reviewed first). This is a sample; recurrent founder variants in a specific population may not appear here - see the full ClinVar listing via the link above.
| Variant (HGVS) | Protein change | Classification | Evidence | Associated condition |
|---|---|---|---|---|
c.1038_1041dup | p.Gly348fs | Pathogenic | ★☆☆☆ | Child syndrome |
c.1098dup | p.Arg367fs | Pathogenic | ★☆☆☆ | CK syndrome |
c.208C>T | p.Gln70Ter | Pathogenic | ★☆☆☆ | not provided |
c.757C>T | p.Gln253Ter | Pathogenic | ★☆☆☆ | Child syndrome |
c.904del | p.Tyr302fs | Pathogenic | ★☆☆☆ | Child syndrome |
c.906C>A | p.Tyr302Ter | Pathogenic | ★☆☆☆ | Child syndrome |
G50R | - | Pathogenic | - | Child syndrome |
c.451G>T | p.Glu151Ter | Pathogenic | - | Child syndrome |
c.544G>C | p.Ala182Pro | Pathogenic | - | Child syndrome |
c.693GAA[1] | p.Lys232del | Pathogenic | - | CK syndrome |
Evidence stars indicate ClinVar review status. Individual variant interpretation should always be performed by a qualified clinical laboratory - many variants remain classified as Variants of Uncertain Significance (VUS) pending more research.
Associated conditions
Pathogenic variants in the NSDHL gene are associated with inherited conditions primarily affecting development and metabolism. One such condition is CHILD syndrome, an X-linked dominant disorder. CHILD syndrome is characterised by issues affecting the development of the limbs and other body parts, typically presenting signs and symptoms mostly on one side of the body. The underlying mechanism involves the disruption of normal cholesterol synthesis, which is crucial for various developmental pathways.
Inheritance pattern
Conditions caused by pathogenic NSDHL variants typically follow x-linked dominant inheritance.
X-linked dominant: all daughters of an affected father inherit the altered X and are affected. Sons receive the father's Y and are unaffected.
UK clinical status
The NSDHL gene is included on several of the NHS national genomic testing panels in the UK, indicating its ascertainment in diagnostic pathways. It is listed as 'green' in DDG2P (a database of genes associated with developmental disorders) and is part of panels for Early onset or syndromic epilepsy (R59), Foetal anomalies (R21), Intellectual disability (R29), Likely inborn error of metabolism (R98), Palmoplantar keratodermas (R166), Peroxisomal disorders, Rare genetic inflammatory skin disorders (R332), Skeletal dysplasia (R104), and Undiagnosed metabolic disorders.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Diet & lifestyle considerations
Maintaining a balanced lifestyle is generally beneficial for overall health, though no specific lifestyle interventions have been conclusively shown to prevent conditions associated with NSDHL gene variants. General population advice suggests a healthy diet and regular physical activity can support metabolic health. Research indicates that dietary cholesterol, while a recognised risk factor for heart disease in high levels, is essential for normal bodily functions and development. However, personalised dietary or lifestyle advice should always come from a qualified healthcare professional.
Supplement considerations
There is currently no conclusive evidence to suggest that specific supplements can prevent or treat conditions associated with NSDHL gene variants. The body's cholesterol synthesis pathway is complex, and disruption due to a gene variant is not typically addressed by over-the-counter supplements. Individuals considering any supplements should consult with a healthcare professional to ensure they are appropriate and safe, especially given the potential for interactions or adverse effects.
Frequently asked questions
What is the primary function of the NSDHL gene?
The NSDHL gene provides instructions for an enzyme involved in cholesterol synthesis, specifically removing a methyl group during the conversion of lanosterol to cholesterol.
What conditions are associated with NSDHL gene variants?
Variants in the NSDHL gene are primarily associated with CHILD syndrome, an X-linked dominant disorder affecting development, particularly of the limbs.
How is the NSDHL gene inherited?
The NSDHL gene is located on the X chromosome, meaning it has an X-linked dominant inheritance pattern.
Why is cholesterol important for the body?
Cholesterol is vital for forming cell membranes, producing hormones and bile acids, and playing a crucial role in embryonic development of tissues like the brain and limbs.
Can diet or supplements help with NSDHL-related conditions?
There is no conclusive evidence that specific diets or supplements can prevent or treat NSDHL-related conditions. Any dietary changes or supplement use should be discussed with a healthcare professional.
References
- Porter FD, Herman GE. Malformation syndromes caused by disorders of cholesterol synthesis. Journal of lipid research. 2011. PMID: 20929975
- Bornholdt D, König A, Happle R. Mutational spectrum of NSDHL in CHILD syndrome. Journal of medical genetics. 2005. PMID: 15689440
- Caldas H, Herman GE. NSDHL, an enzyme involved in cholesterol biosynthesis, traffics through the Golgi and accumulates on ER membranes and on the surface of lipid droplets. Human molecular genetics. 2003. PMID: 14506130
- Porter FD. Human malformation syndromes due to inborn errors of cholesterol synthesis. Current opinion in pediatrics. 2003. PMID: 14631207
- König A, Happle R, Bornholdt D. Mutations in the NSDHL gene, encoding a 3beta-hydroxysteroid dehydrogenase, cause CHILD syndrome. American journal of medical genetics. 2000. PMID: 10710235