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P3H1
prolyl 3-hydroxylase 1
P3H1 is located on the short (p) arm of chromosome 1, at band 1p34.2. Arm ratio per GRCh38 - banding schematic.
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Overview
P3H1 is located on chromosome 1 and encodes prolyl 3-hydroxylase 1, an enzyme that performs post-translational modification of collagen molecules. Collagen serves as the primary structural protein in bone, skin, cartilage, and many other tissues, providing mechanical strength and architectural support. The hydroxylation reaction catalysed by P3H1 occurs within the endoplasmic reticulum before collagen fibres are secreted into the extracellular space. Proper collagen modification is critical for tissue integrity, and disruption of this process can compromise connective tissue function across multiple organ systems. Variants in P3H1 have been identified in individuals with collagen-related disorders, though the gene is not currently included in routine UK carrier screening panels.
What the gene does
Prolyl 3-hydroxylase 1 catalyses the hydroxylation of proline residues at specific positions within collagen alpha chains, converting proline to 3-hydroxyproline. This chemical modification occurs co-translationally as collagen chains are synthesised in the endoplasmic reticulum. The enzyme functions as part of a protein complex alongside cartilage-associated protein (CRTAP) and cyclophilin B (encoded by PPIB), which together coordinate the collagen modification process. The 3-hydroxyproline residues created by P3H1 contribute to thermal stability of the collagen triple helix and influence how collagen molecules interact with one another during fibre assembly. Additionally, P3H1 appears to play a role in regulating the rate of collagen folding, ensuring that triple-helix formation proceeds correctly. Without adequate P3H1 activity, collagen chains may fold improperly or form structurally compromised fibres that cannot provide normal mechanical support to tissues.
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Chromosome location
P3H1 is located at chromosome band 1p34.2 on the short arm of chromosome 1. This chromosomal region contains several genes involved in fundamental cellular processes. The precise exon count and transcript structure for P3H1 vary across different isoforms, reflecting the complexity of collagen-processing pathways. The gene produces a protein that localises primarily to the endoplasmic reticulum, where the majority of collagen biosynthesis occurs.
Protein structure
Domain architecture has not been experimentally characterised in detail for this protein. The prolyl 3-hydroxylase 1 protein contains regions necessary for enzymatic activity and protein-protein interactions required for assembly of the collagen-modifying complex. Structural features enable the enzyme to recognise specific sequences within collagen substrates and position the catalytic machinery appropriately for hydroxylation reactions.
Key variants
Variants in P3H1 range from missense changes affecting single amino acids to deletions and nonsense variants that truncate the protein. Pathogenic variants typically impair the enzyme's ability to hydroxylate collagen substrates or disrupt formation of the functional protein complex. The spectrum of variant effects correlates with clinical severity, with complete loss of function generally producing more pronounced phenotypes than partial activity reduction. Interpretation of P3H1 variants requires consideration of their impact on enzyme activity and collagen stability.
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.105_120del | p.Asp36fs | Pathogenic | ★★☆☆ | Osteogenesis imperfecta type 8 |
c.1051G>T | p.Glu351Ter | Pathogenic/Likely pathogenic | ★★☆☆ | Osteogenesis imperfecta type 8 |
c.1881_1882del | p.Phe627fs | Pathogenic | ★★☆☆ | Osteogenesis imperfecta type 8 |
c.1914+1G>A | - | Pathogenic | ★★☆☆ | Osteogenesis imperfecta type 8 |
c.1918dup | p.Glu640fs | Pathogenic | ★★☆☆ | Osteogenesis imperfecta type 8 |
c.2024G>A | p.Trp675Ter | Pathogenic/Likely pathogenic | ★★☆☆ | P3H1-related disorder |
c.2055+1G>C | V686L | Pathogenic/Likely pathogenic | ★★☆☆ | Osteogenesis imperfecta type 8 |
c.2062del | p.Val688fs | Pathogenic/Likely pathogenic | ★★☆☆ | Osteogenesis imperfecta type 8 |
c.2154del | p.Glu719fs | Pathogenic/Likely pathogenic | ★★☆☆ | Osteogenesis imperfecta type 8 |
c.2164C>T | p.Gln722Ter | Pathogenic/Likely pathogenic | ★★☆☆ | Osteogenesis imperfecta type 8 |
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
Variants in P3H1 have been associated with forms of osteogenesis imperfecta, a group of genetic conditions characterised by bone fragility and connective tissue abnormalities. The clinical presentation can include recurrent fractures, skeletal deformities, short stature, and in some cases features affecting other organ systems such as hearing or dentition. The severity of bone fragility varies considerably depending on how severely P3H1 function is compromised. Because collagen is distributed throughout the body, individuals may experience effects beyond the skeleton, though bone manifestations typically predominate.
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 P3H1 protein do?
The P3H1 protein functions as prolyl 3-hydroxylase 1, an enzyme that adds hydroxyl groups to proline residues in collagen chains. This modification helps stabilise collagen structure and ensures proper assembly of collagen fibres in bone, skin, and other connective tissues.
How is P3H1 inherited?
Inheritance patterns for P3H1-related conditions can vary. Many collagen disorders follow autosomal recessive inheritance, meaning variants must be present in both gene copies for clinical features to manifest, though specific inheritance depends on the variant and associated condition.
Is P3H1 included in UK genetic testing panels?
P3H1 is not currently listed on NHS England Genomic Medicine Service testing panels for routine use. Testing may be available through specialist clinical genetics services when there is specific clinical suspicion of a P3H1-related disorder.