FB2026_01 , released March 12, 2026
FB2026_01 , released March 12, 2026
Human Disease Model Report: mitochondrial trifunctional protein deficiency 2
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General Information
Name
mitochondrial trifunctional protein deficiency 2
FlyBase ID
FBhh0000338
Overview

This report describes mitochondrial trifunctional protein deficiency, HADHB-related. Mitochondrial trifunctional protein deficiency can be caused by mutation in either HADHA or HADHB; in both cases, it exhibits autosomal recessive inheritance. The HADHB gene encodes the beta subunit of the mitochondrial trifunctional protein. There is one fly ortholog, Mtpβ, for which RNAi targeting constructs, alleles caused by insertional mutagenesis, and an amorphic allele created by targeted recombination have been generated. See also the human disease model report for 'mitochondrial trifunctional protein deficiency 1 (FBhh0000337).

The human HADHB gene has not yet been introduced into flies.

Animals homozygous for an amorphic allele of Dmel\Mtpβ have a shorter lifespan and locomotor defects; females exhibit reduced fertility. Neuron-specific knockdown of Mtpβ, effected by RNAi, is also observed to induce abnormal motor neuron terminal morphology and learning disability. Physical and genetic interactions have been described for Mtpβ; see below and in the Mtpβ gene report.

[updated May 2025 by FlyBase; FBrf0222196]

Disease Summary Information
Parent Disease Summary: mitochondrial trifunctional protein deficiency
Symptoms and phenotype

Mitochondrial trifunctional protein deficiency is a rare condition that prevents the body from converting certain fats to energy, particularly when fasting.

Signs and symptoms of mitochondrial trifunctional protein deficiency may begin during infancy or later in life. Features that occur during infancy include feeding difficulties,lethargy, hypoglycemia, hypotonia, and liver problems. Infants with this disorder are also at high risk for serious heart problems, breathing difficulties, coma, and sudden death. Signs and symptoms of mitochondrial trifunctional protein deficiency that may begin after infancy include hypotonia, muscle pain, a breakdown of muscle tissue, and peripheral neuropathy. Problems related to mitochondrial trifunctional protein deficiency can be triggered by periods of fasting or by illnesses such as viral infections. [From Genetics Home Reference, mitochondrial trifunctional protein deficiency, 2016.06.16]

The mitochondrial trifunctional protein, composed of 4 alpha and 4 beta subunits, catalyzes 3 steps in mitochondrial beta-oxidation of fatty acids: long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD), long-chain enoyl-CoA hydratase, and long-chain thiolase activities. Trifunctional protein deficiency is characterized by decreased activity of all 3 enzymes. Clinically, classic trifunctional protein deficiency can be classified into 3 main clinical phenotypes: neonatal onset of a severe, lethal condition resulting in sudden unexplained infant death (SIDS; MIM:272120), infantile onset of a hepatic Reye-like syndrome, and late-adolescent onset of primarily a skeletal myopathy (Spiekerkoetter et al., 2003, pubmed:12754706).

Some patients with MTP deficiency show a protracted progressive course associated with myopathy, recurrent rhabdomyolysis, and sensorimotor axonal neuropathy. These patients tend to survive into adolescence and adulthood (den Boer et al., 2003, pubmed:12838198]).

See also isolated LCHAD deficiency (MIM:609016), which is caused by mutation in the HADHA gene. [From MIM:609015, 2016.06.16]

Specific Disease Summary: mitochondrial trifunctional protein deficiency 2
OMIM report

[MITOCHONDRIAL TRIFUNCTIONAL PROTEIN DEFICIENCY 2; MTPD2](https://omim.org/entry/620300)

Human gene(s) implicated

[HYDROXYACYL-CoA DEHYDROGENASE/3-KETOACYL-CoA THIOLASE/ENOYL-CoA HYDRATASE, BETA SUBUNIT; HADHB](https://omim.org/entry/143450)

Symptoms and phenotype

Mitochondrial trifunctional protein deficiency is a rare condition that prevents the body from converting certain fats to energy, particularly when fasting.

Signs and symptoms of mitochondrial trifunctional protein deficiency may begin during infancy or later in life. Features that occur during infancy include feeding difficulties,lethargy, hypoglycemia, hypotonia, and liver problems. Infants with this disorder are also at high risk for serious heart problems, breathing difficulties, coma, and sudden death. Signs and symptoms of mitochondrial trifunctional protein deficiency that may begin after infancy include hypotonia, muscle pain, a breakdown of muscle tissue, and peripheral neuropathy. Problems related to mitochondrial trifunctional protein deficiency can be triggered by periods of fasting or by illnesses such as viral infections. [From Genetics Home Reference, mitochondrial trifunctional protein deficiency, 2016.06.16]

The mitochondrial trifunctional protein, composed of 4 alpha and 4 beta subunits, catalyzes 3 steps in mitochondrial beta-oxidation of fatty acids: long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD), long-chain enoyl-CoA hydratase, and long-chain thiolase activities. Trifunctional protein deficiency is characterized by decreased activity of all 3 enzymes. Clinically, classic trifunctional protein deficiency can be classified into 3 main clinical phenotypes: neonatal onset of a severe, lethal condition resulting in sudden unexplained infant death (SIDS; MIM:272120), infantile onset of a hepatic Reye-like syndrome, and late-adolescent onset of primarily a skeletal myopathy (Spiekerkoetter et al., 2003, pubmed:12754706). [From MIM:620300, 2025.05.28]

Some patients with MTP deficiency show a protracted progressive course associated with myopathy, recurrent rhabdomyolysis, and sensorimotor axonal neuropathy. These patients tend to survive into adolescence and adulthood (den Boer et al., 2003, pubmed:12838198). [From MIM:620300, 2025.05.28]

Genetics

Mitochondrial trifunctional protein deficiency-2 (MTPD2) is caused by homozygous or compound heterozygous mutation in the HADHB gene, the beta subunit of the mitochondrial trifunctional protein, on chromosome 2p23. [From MIM:620300, 2025.05.28]

Cellular phenotype and pathology
Molecular information

The HADHB gene encodes the beta subunits of the mitochondrial trifunctional protein. The heterocomplex contains 4 alpha and 4 beta subunits and catalyzes 3 steps in mitochondrial beta-oxidation of fatty acids, including the long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) step. The beta subunit harbors the 3-ketoacyl-CoA thiolase activity. (Kamijo et al., 1994, pubmed:8135828). [From MIM:143450, 2025.05.28]

External links
Disease synonyms
mitochondrial trifunctional protein deficiency, HADHB-related
MTPD
MTPD2
Ortholog Information
Human gene(s) in FlyBase
    Human gene (HGNC)
    D. melanogaster ortholog (based on DIOPT)
    Comments on ortholog(s)

    One to one: 1 human to 1 Drosophila.

    Other mammalian ortholog(s) used
      D. melanogaster Gene Information (1)
      Gene Snapshot
      Mitochondrial trifunctional protein β subunit (Mtpβ) encodes a protein involved in fatty acid beta-oxidation. [Date last reviewed: 2019-09-12]
      Gene Groups / Pathways
      Comments on ortholog(s)

      Ortholog of human HADHB (1 Drosophila to 1 human). Dmel\Mtpβ shares 68% identity and 82% similarity with human HADHB.

      Orthologs and Alignments from DRSC
      DIOPT - DRSC Integrative Ortholog Prediction Tool - Click the link below to search for orthologs in Humans
      Other Genes Used: Viral, Bacterial, Synthetic (0)
        Summary of Physical Interactions (5 groups)
        protein-protein
        Interacting group
        Assay
        References
        experimental knowledge based
        anti tag coimmunoprecipitation, peptide massfingerprinting, anti tag western blot
        anti tag coimmunoprecipitation, peptide massfingerprinting, anti tag western blot
        experimental knowledge based
        experimental knowledge based
        Alleles Reported to Model Human Disease (Disease Ontology) (3 alleles)
        Models Based on Experimental Evidence ( 3 )
        Modifiers Based on Experimental Evidence ( 0 )
        Allele
        Disease
        Interaction
        References
        Alleles Representing Disease-Implicated Variants
        Genetic Tools, Stocks and Reagents
        Sources of Stocks
        Contact lab of origin for a reagent not available from a public stock center.
        Bloomington Stock Center Disease Page
        Related mammalian, viral, bacterial, or synthetic transgenes
        Allele
        Transgene
        Publicly Available Stocks
        Selected Drosophila transgenes
        Allele
        Transgene
        Publicly Available Stocks
        RNAi constructs available
        Allele
        Transgene
        Publicly Available Stocks
        Selected Drosophila classical alleles
        Allele
        Allele class
        Mutagen
        Publicly Available Stocks
        ends-out gene targeting
        References (6)