Muscle and skin fibroblast TDP-43 expression, dynamic mutation analysis of NOTCH2NLC and C9orf72 in patients with FOSMN

Background Facial-onset sensory and motor neuronopathy (FOSMN) syndrome is a rare clinical syndrome in which the etiopathogenesis and disease-causing genes remain unknown. In addition, clinical and molecular pathological studies have rarely been evaluated in a large case series. Methods In this study, we present the clinical features and electrodiagnostic findings of the largest cohort of six patients with FOSMN in East Asia to date. Immunofluorescence assessment of TAR DNA-binding protein (TDP)-43 in muscle and skin fibroblasts, detection of GGC trinucleotide repeat expansions in NOTCH2NLC gene, and GGGGCC hexanucleotide repeat expansions in the C9orf72 gene were also performed. Results All patients exhibited typical symptoms and signs of FOSMN syndrome. Almost all patients showed a delayed or absent blink reflex. Neurogenic damage was found in five patients by electromyography. Two of the five patients with muscle and skin biopsies showed TDP-43-positive inclusions in both the nucleus and cytoplasm of muscular tissue and skin fibroblasts. There were no repeat expansions in the C9orf72 or NOTCH2NLC genes in any of the six patients. Conclusions To date, this is the largest FOSMN cohort in East Asia. TDP-43-positive cytoplasmic inclusions in muscle and skin fibroblasts may be a pathologic feature of the disease. The patient’s dynamic mutation test showed no GGC trinucleotide repeat expansions in the NOTCH2NLC and GGGGCC hexanucleotide repeat expansions in the C9orf72 gene. Further studies are needed with more patients.