Clinical characteristics and gene mutation analysis of riboflavin-responsive lipid storage myopathy: report of 3 cases in 2 families and review of literature

Objective The clinical manifestation and electron transfer flavoprotein dehydrogenase ( ETFDH ) gene mutation of riboflavin-responsive lipid storage myopathy were analyzed for early diagnosis and treatment.mutation of riboflavin-responsive lipid storage myopathy were analyzed for early diagnosis and treatment. Methods Clinical material, ETFDH gene mutation and the motor function before and after vitamin B 2 treatment in 3 patients from 2 predigrees were collected from August 2012 to March 2013 in our hospital. Results Case 1 was 16-year-old female. The chief complaint was difficulty of breathing and expectorating for over 3 years. Clinical symptoms included progressive respiratory muscle and proximal limb muscle weakness and worsen by fever, cardiac involvement, myopathic electromyography (EMG) changes and deposition of lipid droplets in muscle fiber by oil red O staining. Case 2 and Case 3 were brothers, the chief complaint of whom was fatigue after exercise for more than 1 year and 1 month, respectively. Clinical symptoms included significantly weakness of lower limbs and neck muscles after exercise and myopathic EMG changes. All 3 patients from two predigrees presented ETFDH gene mutation [c.250G > A (Ala84Thr) homozygous mutations and c.250G > A (Ala84Thr) and c.524G > A (Arg175His) compound heterozygous mutations, respectively]. They all had a dramatic response to vitamin B 2 treatment with muscle strength and motor function recovering to normal. The symptoms of Case 1 were completely disappeared with vitamin B 2 treatment for over 10 months, including respiratory muscle and proximal limb muscle weakness, and the motor function of her limbs returned to normal, characterized by completing over 10 squat-stand in 1 min. Case 2 could walk and run as ordinary people, raise his head without difficulty and play basketball about 2 h without fatigue after vitamin B 2 treatment for over 2 months. Case 3 could participate in any kind of strenuous exercise without fatigue after vitamin B 2 treatment for over 2 months. Conclusions Riboflavin-responsive lipid storage myopathy is mainly characterized by proximal limb and trunk muscle weakness and intolerance of movement, however, rare cases with first symptom of respiratory muscle weakness should also be concerned. In addition, it is a treatable genetic disease. The patients could be cured or significantly improved with vitamin B 2 monotherapy. So vitamin B 2 exploratory treatment should be given when the patients are suspected of riboflavin-responsive lipid storage myopathy. doi: 10.3969/j.issn.1672-6731.2014.06.004