Mild myopathic phenotype in a patient with homozygous c.416C > T mutation in TK2 gene

George K. Papadimas 1, Efthimia Vargiami 2, Pinelopi Dragoumi 2, Rudy Van Coster 3, Joel Smet 3, Sara Seneca 4, Constantinos Papadopoulos 1, Evangelia Kararizou 1, Dimitrios Zafeiriou 2

11st Department of Neurology, Eginition Hospital, Medical School, National and Kapodistrian University of Athens, Greece; 2 1st Department of Pediatrics, Developmental Center “A. Fokas”, Aristotle University of Thessaloniki, “Hippokratio” General Hospital, Thessaloniki, Greece; 3 Division of Pediatric Neurology and Metabolism, Ghent University Hospital, Belgium; 4 Center for Medical Genetics,, Universitair Ziekenhuis Brussel, UZ Brussel, Belgium

The mitochondrial DNA depletion syndrome (MDDS) is characterized by extensive phenotypic variability and is due to nuclear gene mutations resulting in reduced mtDNA copy number. Thymidine kinase 2 (TK2) mutations are well known to be associated with MDDS. Few severely affected cases carrying the c.416C > T mutation in TK2 gene have been described so far. We describe the case of a 14months boy with the aforementioned TK2 gene pathogenic mutation at a homozygous state, presenting with a mild clinical phenotype. In addition to severe mitochondrial pathology on muscle biopsy, there was also histochemical evidence of adenylate deaminase deficiency. Overall, this report serves to further expand the clinical spectrum of TK2 mutations associated with MDDS.

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