FHL1-related clinical, muscle MRI and genetic features in six Chinese patients with reducing body myopathy

Reducing body myopathy is a rare X-linked myopathy characterized by the presence of reducing bodies. The causative gene has been identified as FHL1. We presented with the clinical, muscle magnetic resonance imaging and genetic features of 6 unrelated Chinese patients with reducing body myopathy. We divided the patients into 2 groups according to their age at onset. In addition to limb muscle weakness, pronounced axial muscle involvement was a striking feature common to both groups. Muscle magnetic resonance imaging revealed fatty infiltration predominantly in the postero-medial muscles of the thigh and the soleus muscle of the calf, sparing the gluteus and sartorius muscles. Muscle pathology demonstrated the muscle fibres with reducing bodies distributed in small groups. Genetic analysis revealed FHL1 hemizygote variants in the 6 patients, including 4 novel and 2 reported variants. These variants were located in the LIM2 domain of FHL1 in 4 patients, but 2 located in the LIM4 domain. To the best of our knowledge, this is the first report of reducing body myopathy in the Chinese population. Our findings expand the genetic spectrum of reducing body myopathy.