3-Hydroxy-3-Methylglutaryl CoA (HMG-CoA) lyase Deficiency

Gene : HMGCL

What is 3-Hydroxy-3-Methylglutaryl CoA (HMG-CoA) Lyase Deficiency?

HMG-CoA Lyase deficiency is a disorder caused by a deficiency of the enzyme HMG-CoA Lyase, which is responsible for helping to break down protein. People with this disorder develop symptoms during the first year of their life. These signs include vomiting, diarrhea, dehydration, being tired, and muscle weakness. Certain triggers such as illness, fasting, or eating large amounts of protein can cause episodes of worsening symptoms. During these episodes, people with this disorder develop additional complications, including very low blood sugar, eating and breathing problems, diarrhea, and coma. If left untreated, these episodes can cause brain damage, resulting in intellectual disability. These episodes could also be fatal without treatment. Between episodes, affected children appear normal, though the possibility of developing an enlarged heart or pancreas and vision and hearing loss increases with each episode. If treatment with a strictly managed diet and avoidance of protein and fasting is initiated before symptoms appear, it is possible for affected children to live healthy lives with normal growth and development. However, neurologic damage is still possible during episodes of stress from illness. HMG-CoA Lyase deficiency is caused by pathogenic variants in the HMGCL gene.

How is HMG-CoA Lyase deficiency inherited?

HMG-CoA Lyase deficiency is inherited in an autosomal recessive manner. This type of inheritance requires the presence of two copies of a pathogenic variant in the gene for a person to have the genetic disease. Both parents must be carriers of a pathogenic variant in the gene in order to be at risk to have an affected child. The child must inherit a pathogenic variant from each carrier parent in order to be affected. There is a 1 in 4 chance that a baby will inherit two mutated copies of the gene and be affected when both parents are carriers.

What does it mean to be a carrier?

There are generally no signs or symptoms associated with being a carrier for HMG-CoA Lyase deficiency. However, the risk to have a child affected with HMG-CoA lyase is increased. Testing of reproductive partners is recommended for carriers of HMG-CoA lyase.

How common is HMG-CoA Lyase?

HMG-CoA Lyase deficiency is very rare. It has been identified in fewer than 100 individuals worldwide. Most of the people identified with this disorder are from Saudi Arabia, Portugal, or Spain.

Family References and Resources
Clinician References
What is Analyzed?
  • Full gene sequencing
Affected Systems




Carrier Rates
Detection Rate
Carrier Frequency
General Population 98% 1 in 500

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