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PNPO
pyridoxamine 5'-phosphate oxidase
The PNPO gene provides instructions for an enzyme crucial in the metabolism of vitamin B6, specifically converting inactive forms into the active coenzyme pyridoxal 5'-phosphate (PLP). PNPO is essential for producing the active form of vitamin B6, pyridoxal 5'-phosphate (PLP), which is vital for numerous bodily functions including protein metabolism and neurotransmitter synthesis.
PNPO is located on the long (q) arm of chromosome 17, at band 17q21.32. Arm ratio per GRCh38 - banding schematic.
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Overview
The PNPO gene, or pyridoxamine 5'-phosphate oxidase, encodes an enzyme integral to vitamin B6 metabolism. This enzyme is responsible for synthesising pyridoxal 5'-phosphate (PLP), the biologically active form of vitamin B6, from its precursor forms obtained through diet.
PLP acts as a coenzyme for a wide array of enzymatic reactions throughout the body, playing critical roles in brain function, protein metabolism, and the synthesis of neurotransmitters. Understanding the PNPO gene and its function is important due to its association with certain neurological conditions.
What the gene does
The PNPO gene directs the production of the enzyme pyridoxamine 5'-phosphate oxidase. This enzyme plays a vital role in vitamin B6 metabolism by performing a critical activation step. It converts the dietary forms of vitamin B6, pyridoxine 5'-phosphate and pyridoxamine 5'-phosphate, into pyridoxal 5'-phosphate (PLP).
PLP is the active coenzyme form of vitamin B6 and is essential for numerous enzyme-catalysed reactions throughout human metabolism. These reactions include those involved in protein metabolism and the synthesis of chemicals that transmit signals in the brain, known as neurotransmitters. The PNPO enzyme is expressed in cells across the body, with its highest activity generally observed in the liver [PMID:16520770].
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Chromosome location
The PNPO gene is located on chromosome 17, specifically at position 17q21.32. This genomic address specifies its precise place on the long (q) arm of chromosome 17, within region 2, band 1, sub-band 32 [PMID:12476501].
Protein structure
The PNPO protein, pyridoxamine 5'-phosphate oxidase, is composed of 261 amino acids.
Key variants
Variants in the PNPO gene can lead to altered enzyme function, impacting the body's ability to produce active vitamin B6. These genetic changes can range from single amino acid substitutions to larger deletions or insertions within the gene sequence. Such variants are typically inherited in an autosomal recessive manner.
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.178A>T | p.Lys60Ter | Pathogenic | ★★☆☆ | Pyridoxal phosphate-responsive seizures |
c.246del | p.Leu83fs | Pathogenic | ★★☆☆ | Pyridoxal phosphate-responsive seizures |
c.283C>T | p.Arg95Cys | Pathogenic/Likely pathogenic | ★★☆☆ | Pyridoxal phosphate-responsive seizures |
c.284G>A | p.Arg95His | Pathogenic | ★★☆☆ | Pyridoxal phosphate-responsive seizures |
c.399G>A | p.Trp133Ter | Pathogenic/Likely pathogenic | ★★☆☆ | Pyridoxal phosphate-responsive seizures |
c.412C>T | p.Arg138Cys | Pathogenic/Likely pathogenic | ★★☆☆ | Pyridoxal phosphate-responsive seizures |
c.413G>A | p.Arg138His | Pathogenic/Likely pathogenic | ★★☆☆ | Pyridoxal phosphate-responsive seizures |
c.421C>T | p.Arg141Cys | Pathogenic/Likely pathogenic | ★★☆☆ | Pyridoxal phosphate-responsive seizures |
c.657G>A | p.Trp219Ter | Pathogenic/Likely pathogenic | ★★☆☆ | Inborn genetic diseases |
c.674G>A | p.Arg225His | Pathogenic | ★★☆☆ | Pyridoxal phosphate-responsive seizures |
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 the PNPO gene are primarily associated with pyridoxal phosphate-responsive seizures [PMID:16127118]. This condition, sometimes referred to as pyridoxamine 5'-phosphate oxidase deficiency or PNPO deficiency, typically manifests with seizures developing shortly after birth. These seizures can often be managed through treatment with pyridoxal 5'-phosphate (PLP), the active form of vitamin B6, highlighting the enzyme's critical role.
No disease links recorded for this gene in our reference set.
Inheritance pattern
Conditions caused by pathogenic PNPO variants typically follow autosomal recessive inheritance.
When both parents are carriers, each child has a 25% chance of being affected, 50% of being a carrier, and 25% of being unaffected.
UK clinical status
The PNPO gene is recognised within several UK NHS Genomic Medicine Service (GMS) panels. It holds a 'green' status on the Developmental Disorders Gene2Phenotype (DDG2P) panel, the Early onset or syndromic epilepsy panel, the Likely inborn error of metabolism panel (R98), and the Undiagnosed metabolic disorders panel. This indicates strong evidence for its involvement in these conditions.
Sources: NHS GMS PanelApp · Genomics England PanelApp · NHS National Genomic Test Directory
Frequently asked questions
What is the main function of the PNPO gene?
The PNPO gene provides instructions for an enzyme called pyridoxamine 5'-phosphate oxidase. This enzyme is crucial for converting inactive forms of vitamin B6 into pyridoxal 5'-phosphate (PLP), which is the active form of the vitamin required for many bodily processes.
What happens if the PNPO gene doesn't work correctly?
If the PNPO gene doesn't function correctly, the body cannot produce enough active vitamin B6 (PLP). This can lead to a condition called pyridoxal phosphate-responsive seizures, which often begin shortly after birth and affect brain function.
How is a condition related to PNPO gene variants typically managed?
Conditions caused by PNPO gene variants, such as pyridoxal phosphate-responsive seizures, are often managed by administering pyridoxal 5'-phosphate (PLP) supplements. This provides the body with the active form of vitamin B6 that it cannot produce effectively on its own.
References
- Mills PB, Surtees RA, Champion MP. Neonatal epileptic encephalopathy caused by mutations in the PNPO gene encoding pyridox(am)ine 5'-phosphate oxidase. Human molecular genetics. 2005. PMID: 15772097
- Kang JH, Hong ML, Kim DW. Genomic organization, tissue distribution and deletion mutation of human pyridoxine 5'-phosphate oxidase. European journal of biochemistry. 2004. PMID: 15182361
- Musayev FN, Di Salvo ML, Ko TP. Structure and properties of recombinant human pyridoxine 5'-phosphate oxidase. Protein science : a publication of the Protein Society. 2003. PMID: 12824491