A Novel Variant in the TAMM41-Associated Mitochondrial Myopathy

Pathogenic variants in TAMM41 were recently linked to mitochondrial myopathy, presenting with neonatal hypotonia, generalized weakness, developmental delay, ptosis, and ophthalmoparesis. Here, we present a long-term follow-up of an additional case, a Brazilian patient harboring a novel TAMM41 variant in compound heterozygosity with a previously described pathogenic variant. Patient exhibited mild developmental delay, acquired independent gait, but subsequently developed motor regression and weakness associated with recurrent infections, severe axial involvement, and marked restrictive pulmonary dysfunction. Muscle biopsy revealed decreased COX and SDH staining, which may serve as an important diagnostic clue for this condition. This case expanded the genetic spectrum of TAMM41-related mitochondrial myopathy and provided a brief review of disorders associated with reduced SDH staining.