The alpha-subunit is encoded by the Hydroxyacyl-CoA Dehydrogenase Trifunctional Multienzyme Complex Subunit Alpha (HADHA) gene (OMIM 600890), while the beta-subunit is encoded by the 3-ketoacyl-CoA thiolase, acetyl-CoA acyltransferase (HADHB) gene (OMIM 143450), both genes being nuclear and located on chromosome 2 (2p23.3). Mutations in the HADHA gene typically result in LCHAD deficiency, while mutations in the HADHB gene typically result in rarer MTP deficiencies where all 3 enzymatic functions are lost. (i.e. long-chain enoyl-CoA hydratase, long-chain 3-hydroxyacyl-CoA dehydrogenase, and long-chain 3-ketoacyl-CoA thiolase).
Type of mutations: 
Black: Lethal Cardiomyopathic, Blue: Intermediate-Hepatic, Red: Mild- Neuromuscular.
Suspected pathological mechanism: Pathological mechanism is linked to an energy crisis and incapacity of having a metabolic switch from glucose to lipid.
Diagnostic testing: Identification of biallelic pathogenic variants in HADHB by molecular genetic testing. Elevation of long-chain 3-hydroxyacylcarnitine species in plasma. Targeted molecular genetic testing of the family variants or plasma acylcarnitine profile, plasma free and total carnitine to allow early diagnosis. Immunoblot of HADHB of patients’ fibroblasts showing downregulation of HADHB.
HADHB