# Mitochondrial cardiomyopathy with skeletal muscle myopathy caused by m.3260A > G mutation in MT-TL1 gene: a case report

## TL;DR

A young man with muscle weakness and heart issues was diagnosed with a rare mitochondrial disorder caused by a specific gene mutation.

## Contribution

The case highlights a rare mitochondrial myopathy and cardiomyopathy caused by the m.3260A > G mutation in MT-TL1.

## Key findings

- The patient's symptoms improved with thiamine after other treatments failed.
- The m.3260A > G mutation in MT-TL1 was identified as the cause of mitochondrial cardiomyopathy and skeletal muscle myopathy.

## Abstract

Mitochondrial myopathies are a group of rare hereditary disorders that primarily affect muscle tissue, and present with muscle weakness, fatigue, exercise intolerance, and muscle pain. A key aspect of mitochondrial myopathies is the involvement of different organ systems, such as the cardiovascular system. Various disease features, including clinical and genetic heterogeneity, pose serious difficulties in the diagnostic process. We report a case of a young adult male, who presented with findings that suggested myositis, and was diagnosed with skeletal muscle myopathy and mitochondrial cardiomyopathy, caused by a m.3260A > G variant in the MT-TL1 gene.

A 22-year-old Latvian Caucasian man presented with a half-year history of fatigue, weakness, heaviness in the chest, and loss of breath, as well as a swollen right lower leg for about a week. Laboratory findings revealed increased creatine phosphokinase, creatinine kinase MB, and troponin T levels. All performed autoantibody tests for autoimmune disorders were negative, and no evidence of paraneoplastic syndrome was found. During repeated stays in the hospital, the patient developed heart failure and experienced decreasing muscle strength and muscle pain throughout the whole body. Following an unsuccessful therapy with corticosteroids and later L-carnitine, addition of thiamine lead to an overall improvement in the patient’s condition. Based on the family history, a genetic test was performed, which revealed a m.3260A > G variant in the MT-TL1 gene.

Several factors cause the process of establishing the correct diagnosis of mitochondrial myopathies and cardiomyopathies to be challenging. The presented case aims to raise awareness of rare mitochondrial myopathies, to help clinicians speed up the diagnostic process.

The online version contains supplementary material available at 10.1186/s13256-025-05633-0.