RESUMEN
BACKGROUND: Mitochondrial diseases present with variable multi-organ symptoms. Common disease-causing mutations in mitochondrial DNA (mtDNA) are regularly screened in diagnostic work-up, but novel mutations may remain unnoticed. METHODS: Patients (N = 66) with a clinical suspicion of mitochondrial disease were screened for their mtDNA coding region using conformation sensitive gel electrophoresis and sequencing. Long-PCR was used to detect deletions followed by POLG1 sequencing in patients with multiple deletions. RESULTS: We discovered three novel mtDNA variants that included m.8743G > C, m.11322A > G and m.15933G > A. The novel MTTT variant m.15933G > A is suggested to be pathogenic. Analysis revealed also multiple mtDNA deletions in two patients and five nonsynonymous variants that were putatively pathogenic according to in-silico prediction algorithms. In addition, a rare haplogroup H associated m.7585_7586insT variant was discovered. CONCLUSIONS: Among patients with a suspected mitochondrial disease, a novel MTTT variant m.15933G > A was discovered and is suggested to be pathogenic. In addition, several putatively pathogenic nonsynonymous variants and rare variants were found. These findings highlight the importance of coding region mtDNA screening among patients with clinical features suggesting a mitochondrial disease, but who lack the common mitochondrial disease mutations.
Asunto(s)
ADN Mitocondrial/genética , Enfermedades Mitocondriales/genética , Secuencia de Bases , ADN Polimerasa gamma , ADN Mitocondrial/clasificación , ADN Mitocondrial/metabolismo , ADN Polimerasa Dirigida por ADN/genética , Electroforesis en Gel de Poliacrilamida , Femenino , Haplotipos , Humanos , Masculino , Persona de Mediana Edad , Enfermedades Mitocondriales/patología , Conformación de Ácido Nucleico , Sistemas de Lectura Abierta/genética , Filogenia , Eliminación de SecuenciaRESUMEN
BACKGROUND: Mitochondrial diseases caused by mutations in mitochondrial DNA (mtDNA) affect tissues with high energy demand. Epilepsy is one of the manifestations of mitochondrial dysfunction when the brain is affected. We have studied here 79 Finnish patients with epilepsy and who have maternal first- or second-degree relatives with epilepsy, sensorineural hearing impairment or diabetes mellitus. METHODS: The entire mtDNA was studied by using conformation sensitive gel electrophoresis and PCR fragments that differed in mobility were directly sequenced. RESULTS: We found a common nonsynonymous variant m.15218A > G (p.T158A, MTCYB) that occurs in haplogroup U5a1 to be more frequent in patients with epilepsy. The m.15218A > G variant was present in five patients with epilepsy and in four out of 403 population controls (p = 0.0077). This variant was present in two branches in the phylogenetic network constructed on the basis of mtDNA variation among the patients. Three algorithms predicted that m.15218A > G is damaging in effect. CONCLUSIONS: We suggest that the m.15218A > G variant is mildly deleterious and that mtDNA involvement should be considered in patients with epilepsy and who have a maternal history of epilepsy, sensorineural hearing impairment or diabetes mellitus.
Asunto(s)
ADN Mitocondrial/genética , Diabetes Mellitus/genética , Epilepsia/genética , Pérdida Auditiva Sensorineural/genética , Mitocondrias/genética , Secuencia de Bases , Femenino , Finlandia , Variación Genética , Humanos , Masculino , Enfermedades Mitocondriales/genética , Linaje , Filogenia , Polimorfismo de Nucleótido Simple , Análisis de Secuencia de ADNRESUMEN
BACKGROUND: The genetic background of type 2 diabetes is complex involving contribution by both nuclear and mitochondrial genes. There is an excess of maternal inheritance in patients with type 2 diabetes and, furthermore, diabetes is a common symptom in patients with mutations in mitochondrial DNA (mtDNA). Polymorphisms in mtDNA have been reported to act as risk factors in several complex diseases. FINDINGS: We examined the nucleotide variation in complete mtDNA sequences of 64 Finnish patients with matrilineal diabetes. We used conformation sensitive gel electrophoresis and sequencing to detect sequence variation. We analysed the pathogenic potential of nonsynonymous variants detected in the sequences and examined the role of the m.16189 T>C variant. Controls consisted of non-diabetic subjects ascertained in the same population. The frequency of mtDNA haplogroup V was 3-fold higher in patients with diabetes. Patients harboured many nonsynonymous mtDNA substitutions that were predicted to be possibly or probably damaging. Furthermore, a novel m.13762 T>G in MTND5 leading to p.Ser476Ala and several rare mtDNA variants were found. Haplogroup H1b harbouring m.16189 T > C and m.3010 G > A was found to be more frequent in patients with diabetes than in controls. CONCLUSIONS: Mildly deleterious nonsynonymous mtDNA variants and rare population-specific haplotypes constitute genetic risk factors for maternally inherited diabetes.
Asunto(s)
ADN Mitocondrial/genética , Diabetes Mellitus Tipo 2/genética , Madres , Polimorfismo Genético , Adulto , Secuencia de Bases , Estudios de Casos y Controles , Complejo I de Transporte de Electrón/genética , Electroforesis en Gel de Poliacrilamida , Femenino , Finlandia , Predisposición Genética a la Enfermedad , Haplotipos , Herencia , Humanos , Masculino , Persona de Mediana Edad , Proteínas Mitocondriales/genética , Datos de Secuencia Molecular , Linaje , Medición de Riesgo , Factores de Riesgo , Análisis de Secuencia de ADN , Adulto JovenRESUMEN
The 8993T-->C mutation in mitochondrial DNA (mtDNA) has been described previously to be associated with infantile- or childhood-onset phenotypes, ranging from Leigh's syndrome to neurogenic weakness, ataxia, and retinitis pigmentosa syndrome. We report a kindred with adult-onset slowly progressive ataxia and polyneuropathy and with the heteroplasmic 8993T-->C mutation. Our findings suggest that the 8993T-->C mtDNA mutation should be considered in the differential diagnosis of nondominant adult-onset ataxia and axonal neuropathy.