Molecular and phenotypic heterogeneity in mitochondrial trifunctional protein deficiency due to beta-subunit mutations.
The mitochondrial trifunctional protein (TFP) is a multienzyme complex of the fatty acid beta-oxidation cycle. It is composed of four alpha-subunits (HADHA) harboring long-chain enoyl-CoA hydratase and long-chain L-3-hydroxyacyl-CoA dehydrogenase (LCHAD) and four beta-subunits (HADHB) harboring long-chain 3-ketoacyl-CoA thiolase (LKAT). Mutations in either subunit can result in TFP deficiency with reduced activity of all three TFP enzymes. We characterize 15 patients from 13 families with beta-subunit mutations by clinical, biochemical, and molecular features. Three clinical phenotypes are apparent: a severe neonatal presentation with cardiomyopathy, Reye-like symptoms, and early death (n=4); a hepatic form with recurrent hypoketotic hypoglycemia (n=2); and a milder later-onset neuromyopathic phenotype with episodic myoglobinuria (n=9). Maternal HELLP syndrome occurred in two mothers independently of the fetal phenotype. Mutational analysis revealed 16 different mutations, the majority being missense mutations (n=12). The predominance of missense mutations and the milder myopathic phenotype are consistent. Based upon homology to yeast thiolase that has been characterized structurally, the mutation localization within the protein correlates with the clinical phenotype. Outer loop mutations that are expected to alter protein stability less were only present in milder forms. The degree of reduction in thiolase antigen also correlated with the severity of clinical presentation. Although TFP deficiency is highly heterogeneous, there is genotype-phenotype correlation.
Spiekerkoetter
Ute
U
Department of Pediatrics and Vanderbilt Children's Hospital, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA.
Sun
Bin
B
Khuchua
Zaza
Z
Bennett
Michael J
MJ
Strauss
Arnold W
AW
D000293:Adolescent; D000328:Adult; D000595:Amino Acid Sequence; D015153:Blotting, Western; D002648:Child; D002675:Child, Preschool; D004252:DNA Mutational Analysis; D005091:Exons / Q000235:genetics; D005260:Female; D005347:Fibroblasts; D018740:Genetic Heterogeneity; D005838:Genotype; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D063991:Mitochondrial Trifunctional Protein; D063992:Mitochondrial Trifunctional Protein, alpha Subunit; D063993:Mitochondrial Trifunctional Protein, beta Subunit; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000737:chemistry / Q000172:deficiency* / Q000235:genetics*; D009154:Mutation / Q000235:genetics*; D010641:Phenotype; D021122:Protein Subunits / Q000737:chemistry / Q000172:deficiency* / Q000235:genetics*; D012441:Saccharomyces cerevisiae / Q000201:enzymology; D013577:Syndrome
D009097:Multienzyme Complexes; D021122:Protein Subunits; C576205:HADHA protein, human; D063992:Mitochondrial Trifunctional Protein, alpha Subunit; C576206:HADHB protein, human; D063991:Mitochondrial Trifunctional Protein; D063993:Mitochondrial Trifunctional Protein, beta Subunit