Hereditary neuropathy or pain disorder

Gene: CPOX

Green List (high evidence)

Comment on mode of inheritance: As reviewed by Sharon Whatley, variants in CPOX may cause autosomal dominant or autosomal recessive porphyria. Monoallelic variants in CPOX have very low clinical penetrance (<1%) and may be challenging to report as diagnostic. Hence, BIALLELIC, autosomal or pseudoautosomal MOI would be more appropriate. This gene has been tagged for MOI Expert Review. CPOX is associated with Coproporphyria 121300 (AR and AD) and Harderoporphyria 618892 (AR) in OMIM (accessed 20th Oct 2025).

Created: 4 Nov 2025, 1:47 p.m. | Last Modified: 4 Nov 2025, 1:47 p.m.

Panel Version: 7.29

Comment on list classification: Both mono- and bi- allelic variants in CPOX are known to cause hereditary coproporphyria (HCP), which may result in severe abdominal pain and progressive peripheral neuropathy. However, specific neuropathy cases are rarely reported with a genetic diagnosis - only 1 individual with peripheral neuropathy and a heterozygous CPOX variant is included in this review (PMID: 35228944 Upchurch et al., 2025). Biochemical testing of faecal coproporphyrin is a much more common diagnostic route. Since CPOX is the only gene known to cause Coproporphyria, this gene may remain Green for Hereditary neuropathy or pain disorder.

Created: 21 Oct 2025, 3:38 p.m. | Last Modified: 21 Oct 2025, 4:06 p.m.

Panel Version: 7.20

HCP patients may present with acute neurovisceral attacks, characterised by severe abdominal pain and neuropsychiatric symptoms - often provoked by drugs, alcohol, or endocrine factors. Diagnosis of HCP is established based on increased faecal coproporphyrin III:I ratio when VP has been excluded by the plasma fluorescence scan wavelength (PMID: 11309681 Lamoril et al., 2001; 38940544 Aarsand et al., 2022). Acute episodes can progress to include seizures, peripheral motor neuropathy and posterior reversible encephalopathy syndrome if left untreated (PMID: 35584894 Schulenburg-Brand et al., 2022)

PMID: 8008008 Barohn et al. 1994
A 23-year-old man with no genetic diagnosis. Presented with epilepsy and a past history of abdominal pain. Electrophysiologic studies demonstrated a peripheral neuropathy with features of axonal degeneration and demyelination.

PMID: 11074238 Kuhnel et al., 2000
53 patients with HCP. Phenotype: abdominal pain (89% of the cohort), neurologic (33%), psychiatric (28%), cardiovascular (25%), and skin symptoms (14%).

PMID: 21103937 Hasanoglu 2011
Male infant from a Turkish consanguineous family presented with the Harderoporphyria phenotype: neonatal hyperbilirubinemia, hemolytic anemia, hepatosplenomegaly, and skin lesions when exposed to UV light. Heterozygous for c.980A>G (p.His327Arg) The patient died at 5 months old due to an apparent acute neurologic porphyric attack. Structural studies predicted that p.H327R interacts with residue W399 in the CPOX active site.

PMID: 24353603 Chen et al., 2013
46yo Chinese woman with a biochemical diagnosis of HCP. Phenotype: acute abdominal pain and progressive bilateral weakness and pain in the limbs. She also experienced significant muscle atrophy and decreased strength. Nerve conduction potential study revealed motor-sensory polyneuropathy. Successfully treated with hemin.

PMID: 24156084 Jiménez-Jiménez et al., 2013
44-year-old patient presenting clinically with acute ataxia who was diagnosed with HCP. Heterozygous for p.Q306X.

PMID: 35228944 Upchurch et al., 2025
26-year-old female with HCP who presented with acute ascending flaccid paralysis and respiratory failure after COVID-19 infection and was initially misdiagnosed and treated for Guillain-Barré syndrome. Patient developed progressively worsening abdominal pain; symmetric, distal-predominant, and ascending weakness developed four weeks later, associated with severe headaches and complex visual hallucinosis. Electrodiagnostic testing: profound axonal sensorimotor peripheral polyneuropathy affecting all extremities. No abnormalities on brain MRI. Successfully treated with hemin. Heterozygous for c.1070G>A (p.Cys357Tyr) - rare in gnomAD v4, Revel score = 0.9. Seq method: unknown.

CPOX is associated with Coproporphyria 121300 (AR and AD) and Harderoporphyria 618892 (AR) in OMIM (accessed 21st Oct 2025).

Created: 21 Oct 2025, 3:35 p.m. | Last Modified: 21 Oct 2025, 4:03 p.m.

Panel Version: 7.20

Mode of inheritance
BIALLELIC, autosomal or pseudoautosomal

Phenotypes
Coproporphyria, OMIM:121300; Harderoporphyria, OMIM:618892

Publications

• 8008008
• 11074238
• 11309681
• 21103937
• 24353603
• 24156084
• 35228944
• 35584894
• 38940544

Green List (high evidence)

Relevant metabolic investigation: Urine porphobilinogen

PMID: 38940544 Aarsand reports that the acute porphyrias are a group of rare inborn errors of metabolism caused by abnormal functioning of haem biosynthesis enzymes and are associated with acute neurovisceral attacks characterized by severe abdominal pain and neuropsychiatric symptoms that may require highly specialized intensive care. The acute porphyrias, acute intermittent porphyria (AIP), variegate porphyria (VP) and hereditary coproporphyria (HCP), usually become symptomatic in early adulthood.

PMID: 11309681 Lamoril reports that HCP is the least common of the autosomal dominant, acute hepatic porphyrias. It results from pathogenic variants in the CPOX gene that encodes the mitochondrial enzyme, coproporphyrinogen oxidase.

PMID: 38940544 Aarsand and 23605133 Whatley report that HCP is an autosomal dominant disorder with an estimated prevalence of HCP in the UK as 1–2 in a million with a rough estimate of the clinical penetrance of 0.4%. Due to this low penetrance, genetic testing alone may be misleading and cause misdiagnosis. IPNET advises that biochemical testing is used to diagnose active HCP as the penetrance is so low.

PMID: 35584894 Schulenburg-Brand reviews the neuropathy that may occur in the acute porphyrias. Weakness and altered sensation are typically mild in an acute attack and improve as the pain resolves. In a small number of cases, severe, progressive peripheral neuropathy develops. Neuropathy can worsen, even after the acute pain resolves, with a Guillain-Barré like picture. Proximal muscle weakness occurs in the upper limbs and can progress to involve the legs and cause respiratory failure. Cranial nerves can be involved, with the facial, vagus and hypoglossal nerves most often affected, causing swallowing difficulties. Sensory neuropathy is less common, but can cause numbness over the torso and thighs, sometimes with severe pain. Cases gradually resolve with respiratory support, and some patients may need prolonged mechanical ventilation. After recovery, some degree of peripheral neuropathy can persist, with foot drop and wrist drop being fairly typical.

Careful consideration should be given to the reporting of a single pathogenic variant as an incidental finding in the CPOX gene, due to its low clinical penetrance (~0.4%).

Created: 11 Sep 2025, 10:23 a.m. | Last Modified: 11 Sep 2025, 10:24 a.m.

Panel Version: 7.8

Mode of inheritance
BOTH monoallelic and biallelic (but BIALLELIC mutations cause a more SEVERE disease form), autosomal or pseudoautosomal

Phenotypes
121300; 618892

Publications

• 38940544
• 11309681
• 23605133
• 35584894

The mode of inheritance of this gene has been updated toBOTH monoallelic and biallelic, autosomal or pseudoautosomalfollowing NHS Genomic Medicine Service approval.

Created: 1 Feb 2023, 10:16 a.m. | Last Modified: 1 Feb 2023, 10:16 a.m.

Panel Version: 2.18

MOI should be changed from "MONOALLELIC, autosomal or pseudoautosomal, NOT imprinted" to "BOTH monoallelic and biallelic, autosomal or pseudoautosomal" as Biallelic variants also cause disease.

Created: 26 Oct 2021, 10:42 a.m. | Last Modified: 26 Oct 2021, 10:42 a.m.

Panel Version: 1.64

Mode of inheritance
BOTH monoallelic and biallelic, autosomal or pseudoautosomal

Green List (high evidence)

Gene rated Green : From feedback from Genomics England Clinical team (Anna de Burca and Meriel McEntagart). Extension of panel scope - syndrome with non-neurological features / Broader phenotype - porphyria, can present similar to AIP according to Alex Rossor. Promote to Green as management implications

Created: 6 Dec 2019, 3:33 p.m. | Last Modified: 6 Dec 2019, 8:47 p.m.

Panel Version: 0.73

Comment on list classification: This gene has changed ratings because the panel for R78 was going to be a broad panel (to include conditions where neuropathy is part of a more complex phenotype or where there is overlap with another neurological presentation eg. HSP) but subsequently during the follow up call on 21st June with the Test Group it was agreed that it was more clinically relevant for R78 to be restricted to genes that are associated with isolated neuropathy, which this panel represents. For genes that represent the broader phenotype see https://panelapp.genomicsengland.co.uk/panels/85/.

Created: 6 Dec 2019, 3:17 p.m. | Last Modified: 6 Dec 2019, 3:17 p.m.

Panel Version: 0.42

Review and rating uploaded from file (Curation_Template_GMS_Neuro_AR_20190521.xlsx) submitted by Alex Rossor (UCL Institute of Neurology) on behalf of London North GLH for GMS Neurology specialist test group.

Created: 11 Jun 2019, 1:40 p.m.

Green List (high evidence)

Mode of inheritance
MONOALLELIC, autosomal or pseudoautosomal, NOT imprinted

Phenotypes
Skin photosensitivity and haemolytic anaemia. Can present acutely similar to AIP