GENE REFERENCE / HGNC:4982

HMBS

hydroxymethylbilane synthase

protein-coding gene11q23.3Gene information

What does this gene do?

The HMBS gene provides instructions for making an enzyme known as hydroxymethylbilane synthase. This enzyme is involved in the production of a molecule called heme. Heme is vital for all of the body's organs, although it is most abundant in the blood, bone marrow, and liver. Heme is an essential component of iron-containing proteins called hemoproteins, including hemoglobin (the protein that carries oxygen in the blood).

The production of heme is a multi-step process that requires eight different enzymes. Hydroxymethylbilane synthase is responsible for the third step in this process, which combines four molecules of porphobilinogen (the product of the second step) to form a compound called hydroxymethylbilane. In subsequent steps, five other enzymes produce and modify compounds that ultimately lead to heme.

Source: MedlinePlus, National Library of Medicine. Source publication: 2020-08-18. Source review: 2009-07.

ClinGen reviews

ClinGen reviews the evidence linking a particular gene to a condition. Each rating below describes the strength of that link. It does not classify a variant in your DNA file.

Condition	Inheritance	Evidence
acute intermittent porphyriaMONDO:0008294 · Evaluated 2022-05-27	Semidominant	DefinitiveGeneral Inborn Errors of Metabolism Gene Curation Expert Panel

ClinVar records

These numbers show what has been submitted to ClinVar. They cannot tell you how likely you are to have a condition.

Submitted alleles: 808
Submissions for variants in or overlapping this gene: 1,200
Submissions explicitly reporting this gene: 1,137
Alleles reported pathogenic / likely pathogenic: 181
VariationIDs with uncertain significance: 285
VariationIDs with conflicting classifications: 24

The rows count different things: alleles, submissions or VariationIDs. Their categories can overlap, so do not add them together. Pathogenic/likely pathogenic counts exclude structural variants that merely overlap a gene. A dash in the source means “not reported,” not zero.

NCBI produces the gene-summary file each week using counts recorded at the start of the month. The numbers may differ from those on the live ClinVar website. Read the field definitions ↗

View this gene in ClinVar ↗

YOUR DNA FILE

Can your DNA file tell you about HMBS?

From a DNA test kit (such as 23andMe, AncestryDNA or MyHeritage). These kits check a fixed list of about 600,000 to 700,000 positions across your whole genome. ClinVar lists 181 alleles in HMBS reported as pathogenic or likely pathogenic. A kit checks only some of these positions, and often none of them.

From whole genome sequencing (a VCF file). Sequencing reads most of your genome. Your file lists the places where your DNA differs from the reference genome. Some regions are hard to sequence, including parts of some genes that have near-identical copies elsewhere, and a VCF file does not record which positions were read well.

If a variant is not in your file, that does not mean you don’t have it.

What BioDecode checks

BioDecode compares every variant in your file with ClinVar, on your own computer. For each match, it shows the ClinVar classification, the review status and the condition it was reported for. Your file is not uploaded.

A ClinVar classification applies to one particular variant and the condition it was reported for. It does not tell you about other variants in HMBS.

BioDecode cannot fill gaps in your test, diagnose a condition or replace clinical testing.

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