Gene
HMBS
hydroxymethylbilane synthase
- HGNC 4982(opens in a new tab)
- Ensembl gene ENSG00000256269(opens in a new tab)
- NCBI Gene 3145(opens in a new tab)
Summary
- Cytogenetic location
- 11q23.3
- Coordinates
- Chromosome 11: 119,084,881–119,093,549 (GRCh38)
- Exons
- 14 exons across 8.7 kb
- Protein
- 361 amino acids
- Previous symbols
- PBGD, UPS, PORC
- MANE Select transcript
- ENST00000652429.1NM_000190.4
- Locus type
- gene with protein product
- Very high
- Confident
- Low
- Very low
Reference genomeGRCh38hg38
Positions on gene and variant pages follow this choice, in this browser.
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Get my Genome TestCurated reports relevant to this gene
Hepatic Porphyria Disorders
- Hepatic Porphyria
A group of metabolic diseases due to deficiency of one of a number of liver enzymes in the biosynthetic pathway of heme. They are characterized by the accumulation and increased excretion of porphyrins or its precursors. Clinical features include neurological symptoms (porphyria, acute intermittent), cutaneous lesions due to photosensitivity (porphyria cutanea tarda), or both (hereditary coproporphyria). Hepatic porphyrias can be hereditary or acquired as a result of toxicity to the hepatic tissues.
- ClinGen rates the link definitive
- 4 GenCC submitters rate it definitive or strong
Porphyria
Porphyria is a group of diseases in which substances called porphyrins build up, negatively affecting the skin or nervous system. Most types are inherited, but porphyria cutanea tarda may also be due to increased iron in the liver, hepatitis C, alcohol, or HIV/AIDS.
- ClinGen rates the link definitive
- 4 GenCC submitters rate it definitive or strong
What knowing changes
Attack prevention through trigger avoidance, IV dextrose or hemin during acute attacks, RNA interference therapy (givosiran), genetic counseling
How HMBS is laid out
- Coding sequence
- Untranslated region
- Intron
- Direction of transcription
- Known disease-causing sites
Exons of the gene's MANE Select transcript (release v1.5), from NCBI and EMBL-EBI, on the GRCh38 reference genome.
Chromosome bands from UCSC's GRCh38 ideogram (2022-10-29).
Nearby genes from Ensembl release 116, on GRCh38.
Exons make up 1.5 kb of the gene's 8.7 kb; 1,086 of those bases code for the protein.
How a genome test reads HMBS
39
positions in HMBS where ClinVar classes a change as pathogenic or likely pathogenic
None of them falls in a region short reads find hard.
A whole genome covers all 8.7 kb of HMBS, introns included, not only the 1.5 kb of exons.
Traits linked to HMBS
The Human Phenotype Ontology lists these as features of the rare conditions HMBS can cause. Each trait's page lists the other genes linked to it.
Abnormality of the nervous system
- Apraxia
- Ataxia
- Babinski sign
- Degeneration of cerebellum
- Delayed CNS myelination
- Loss of ability to walk
- Nerve damage causing decreased feeling and movement
- Unsteady walk
Show 30 more traits
- Cognitive impairment
- Cranial nerve paralysis
- Decreased reflex response
- Delayed ability to walk
- Febrile seizure (within the age range of 3 months to 6 years)
- Global developmental delay
- Intention tremor
- Mental deterioration
- Partial absence of cerebellar vermis
- Peripheral neuropathy
- Anxiety
- Brain imaging abnormality
- Confusion
- Depression
- Difficulty staying or falling asleep
- Epilepsy
- Excessive daytime sleepiness
- Hallucinations
- Memory impairment
- Motor axonal neuropathy
- Motor polyneuropathy
- Paranoia
- Restlessness
- Somatic sensory dysfunction
- Coma
- Tremor
- Acute episodes of neuropathic symptoms
- Paralysis
- Pins and needles feeling
- Psychotic episodes
Laboratory abnormality
- Elevated urinary coproporphyrin level
- Increased urine urobilinogen
- Abnormal circulating enzyme concentration or activity
- Elevated urinary delta-aminolevulinic acid
- Increased urinary porphobilinogen
- Porphyrinuria
- High blood bilirubin levels
- Increased CSF lactate
Show 5 more traits
Abnormality of the digestive system
- Abdominal pain
- Constipation
- Enlarged liver
- Nausea and vomiting
- Abdominal bloating
- Diarrhea
- Hepatocellular carcinoma
- Ileus
Show 4 more traits
Abnormality of the musculoskeletal system
- Low muscle tone in trunk
- Spastic paraparesis
- Back pain
- Hunched back
- Limb pain
- Respiratory paralysis
- Weakness of muscles of respiration
- Weakness of outermost muscles
Show 1 more trait
External links
Gene records
Transcript
Protein
Where this comes from
- HGNC: the gene's symbol, name, other symbols and location.
- MANE Select v1.5, from NCBI and EMBL-EBI: the transcript, its exons and coding sequence.
- GenCC and ClinGen, released 2026-10-16: which conditions the gene is linked to, and how strongly.
- The ACMG secondary findings list, SF v3.2.
- ClinVar and the GIAB stratifications: known disease-causing sites, and the regions short reads find hard.
- The Human Phenotype Ontology, release 2026-09-01: the traits linked to the gene. Find out more at hpo.jax.org.
- Data release 2026.10.16-c6eea6bf.
Cite this page
Dante Labs. (n.d.). HMBS gene: hydroxymethylbilane synthase. Retrieved 17 October 2026, from https://dantelabs.com/genes/hmbs
Dante Labs. HMBS gene: hydroxymethylbilane synthase [Internet]. [cited 17 October 2026]. Available from: https://dantelabs.com/genes/hmbs
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