ClinVar

Wong et al. (2006) identified a heteroplasmic 12207G-A transition in the MTTS2 gene in a girl with clinical features of both MERRF (545000) and MELAS (540000) syndromes. Skeletal muscle studies showed ragged red fibers, significant pleomorphic mitochondrial proliferation, complex I deficiency (see 252010), and 92% mutation load. The 12207G-A mutation occurs at the first nucleotide of the 5-prime end of the molecule, which is involved in the formation of the stem region of the amino acid acceptor arm. The mutation was not found in the unaffected mother's peripheral blood or hair follicles nor in 200 controls. Wong et al. (2006) suggested that the mutation likely affects proper processing of the precursor MTTS2 mRNA and may also affect neighboring genes. Clinically, the patient showed severe developmental delay, feeding difficulties, recurrent infections, basal ganglia lesions, cerebral atrophy, proximal muscle weakness, increased serum lactate, and liver dysfunction.