“Introduction:  Lipid myopathies are rare diseases that can present acutely with rhabdomyolysis triggered by several factors or as chronic conditions characterized by myalgias and exercise intolerance. Disease onset can occur in all ages, from early stages of life to late-adult onset. Overall, genes involved in lipid myopathies can be distinguished in those involved in mitochondrial function and others coding for cytoplasmatic factors. Some of them, like forms associated to ACAD9 mutations, VLCAD and MADD, show clinical benefit from integration with riboflavin.

Case study: We present the case of a 20-year-old male patient with no family history ofneuromuscular diseases, that started complaining of exercise intolerance and hyperCKemia. The lactic acid and ammonia dosage after effort in ischemic conditions was normal and his ower limb muscle MRI was unremarkable. Muscle biopsy showed presence of multiple lipid vacuoles positive at Oil red O staining, confirmed at electron microscopy. He was then tested for several genetic
metabolic myopathies by NGS panel including ACADVL, AGL, AMPD1, CPT2, ETFA, ETFB, ETFDH, GBE1, GYS1, GYS2, LDHA, PFKM, PGK1, PHKA1, PNPLA2, PYGM and SLC22A5 genes, all negative. Also, plasmatic acylcarnitines and aminoacids did not show significant variations. We introduced treatment with riboflavin with ex juvantibus criteria and the patient experienced a nearly complete remission of symptoms.

Conclusions: Histopathology and clinical features are consistent with a lipid myopathy responsive to riboflavin integration. Given the normal results obtained by analysis of VLCAD and MADD associated genes, we plan to study the ACAD9 gene among others with an extended panel for lipid myopathies.”