A novel mitochondrial ATP8 gene mutation in a patient with apical hypertrophic cardiomyopathy and neuropathy

Abstract

Purpose: To identify the biochemical and molecular genetic defect in a 16-year-old patient presenting with apical hypertrophic cardiomyopathy and neuropathy suspected for a mitochondrial disorder. Methods: Measurement of the mitochondrial energygenerating system (MEGS) capacity in muscle and enzyme analysis in muscle and fibroblasts were performed. Relevant parts of the mitochondrial DNA were analysed by sequencing. Transmitochondrial cybrids were obtained by fusion of 143B206 TK 2 rho zero cells with patient-derived enucleated fibroblasts. Immunoblotting techniques were applied to study the complex V assembly. Results: A homoplasmic nonsense mutation m.8529GRA (p.Trp55X) was found in the mitochondrial ATP8 gene in the patient's fibroblasts and muscle tissue. Reduced complex V activity was measured in the patient's fibroblasts and muscle tissue, and was confirmed in cybrid clones containing patient-derived mitochondrial DNA. Immunoblotting after blue native polyacrylamide gel electrophoresis showed a lack of holocomplex V and increased amounts of mitochondrial ATP synthase subcomplexes. An in-gel activity assay of ATP hydrolysis showed activity of free F 1 -ATPase in the patient's muscle tissue and in the cybrid clones. Conclusion: We describe the first pathogenic mutation in the mitochondrial ATP8 gene, resulting in an improper assembly and reduced activity of the complex V holoenzyme.Mitochondrial (mt) ATP synthase, or complex V (EC 3.6.3.14), uses the proton gradient provided by the activity of the respiratory chain enzymes complexes I, III and IV for ATP synthesis, thereby generating .95% of cellular ATP.

Subcomplexes of mitochondrial complex V reveal mutations in mitochondrial DNA

“…More recently, complex V subcomplexes were also identified in a patient with a mutation in the mitochondrial MT-ATP8 gene [21]. Contrary to the finding of subcomplexes in our patients with mitochondrial tRNA mutations (Table 1, patients 1-12), Carrozzo et al could not detect subcomplexes of complex V in any of seven patients carrying a mitochondrial tRNA mutation [20].…”

Mitochondrial centrality in heart failure

“…Furthermore, clinical evidence indicating that mitochondrial bioenergetic metabolism may be critical and primary in the development of HF has come from the identification in individuals with a variety of cardiomyopathies of specific nuclear gene defects in mitochondrial/ metabolic proteins including ANT, respiratory complex enzyme subunits, molecules involved in complex IV assembly and FAO enzymes (Table 1). Specific mtDNA gene defects associated with clinical CM/HF (often with associated neuropathy) have also been identified in tRNA genes [28], although mutations in structural genes such as ATP6/ATP8 and cytb (mitochondrial genes encoding subunits of complexes V and III, respectively) can also lead to CM/HF [29][30][31].…”

Multisystem manifestations of mitochondrial disorders

“…Mutations at nucleotide 8,993 in the mtDNA-encoded ATP6 subunit of complex V are associated with a neurological presentation of either neuropathy ataxia and retinitis pigmentosa or maternally inherited Leigh's syndrome [111]. A recent report describes a patient with hypertrophic cardiomyopathy and neuropathy and the first pathogenic (homoplasmic) point mutation in ATP8, the second mtDNA-encoded gene of complex V [59].…”

“…Petechiae and acrocyanosis are common features in infants carrying mutations in the mitochondrial ETHE1 gene (Table 3). [8,47,52,96] NDUFV2 [15] tRNA Ile [23,96,112] NDUFS2 [65] tRNA Lys [95,96] NDUFAF1 [33] tRNA Leu(CUN) [45] TAZ (Barth's syndrome) [18] Single deletion/duplication [96,131,135] SCO2 [57,82] Cytochrome b [118] COX15 [7,39] ATP8 [59] X25 frataxin [22,110] Diabetes tRNA Leu(UUR) [1,66,70,121,128] X25 frataxin [22,40] tRNA Lys [1,60,66,128] tRNA Glu [48,49] Single deletion/duplication [11,92] PEO1 [98] POLG1 [25,54] DGUOK [68] MPV17 [107] Nephropathy tRNA Leu(UUR) [46,…”