A Tunisian POLG mutation expands the clinical spectrum of POLG-related disorders

Mitochondrial Neuro-Gastro-Intestinal Encephalopathy (MNGIE) is a rare and fatal mitochondrial disorder caused by biallelic mutations in the TYMP gene. In rare cases, it can be caused by pathogenic variants in the POLG gene, with a clinical presentation similar to that of TYMP-related MNGIE, except for the absence of leukoencephalopathy. Here we report the cases of six Tunisian patients presenting with a homogeneous clinical MNGIE-like phenotype, characterized by an early infantile onset. Key features included psychomotor delay or regression, peripheral neuropathy, gastrointestinal disturbances, hypotrophy or growth retardation, and elevated cerebrospinal fluid protein levels. All patients originated from the same governorate and carried the same homozygous POLG variant c.2391G > T (p.Met797Ile), which may suggest a founder effect.