The variable symptoms of mitochondrial diseases make it challenging for physicians trying to diagnose a condition. To aid their work, researchers identified clinical and molecular symptoms typical of patients carrying a specific mitochondrial mutation, and suggested genetic testing be performed when these symptoms are present.
The study,“Clinical and Molecular Characteristics in 100 Chinese Pediatric Patients with m.3243A>G Mutation in Mitochondrial DNA,” published in the Chinese Medical Journal, identified a range of symptoms that could be used as an indicator of mitochondrial disease, prompting genetic testing to speed up the diagnosis.
Patients in the study were all children with a mutation called m.3243A>G. The mutation is known to cause a condition known as MELAS (mitochondrial encephalomyopathy with lactic acidosis and stroke‑like episodes), and is one of the most common mutations affecting mitochondrial DNA.
Researchers at Peking University First Hospital in China reviewed medical charts of 100 children treated at the hospital from 2007 to 2013. Medical charts were analyzed retrospectively, and researchers found that more than 60 percent of patients waited an average of two years to get a diagnosis. Most patients had several different symptoms, and the most common were seizures, followed by short stature, elevated plasma lactate, abnormal brain imaging findings, vomiting and other stomach problems, vision problems, headache, and muscle weakness.
Each symptom affected nearly half or more of the group, with 76 percent of children having seizures. Other less common symptoms included difficulties in balance or stability, exercise intolerance, and heart disease, present in 35 percent of the children. Another 21 percent had hearing problems and 18 percent had drooping eyelids.
Since mitochondrial DNA is inherited and copied separately from the nuclear DNA, not all cells need to be affected by a mitochondrial mutation. Researchers found that the proportion of white blood cells holding mutated mitochondria corresponded to the age of onset of symptoms, so that children with more affected cells became sick earlier.
Grouping symptoms according to the proportion of affected cells showed that muscle issues were more common in children with more mutated mitochondria. Those with low or medium levels of mutations, in contrast, were more likely to have hearing loss, decreased vision, and stomach problems.