This article discusses a case of 5,10-Methylenetetrahydrofolate reductase (MTHFR) deficiency, a rare autosomal recessive disorder, presenting as adult-onset spastic paraplegia. MTHFR deficiency is characterized by low plasma methionine levels, hyperhomocysteinemia, and homocysteinuria. The clinical symptoms of MTHFR deficiency can vary widely, from severe neurodevelopmental delays to gait disorders. The case study highlights the clinical heterogeneity of MTHFR deficiency and emphasizes the need for clinicians to be aware of this rare disease. The patient in the case study was treated with multivitamins, folate, and methylcobalamin, resulting in significant improvement in symptoms and biochemical abnormalities. The article concludes by stating that this case expands the understanding of MTHFR mutations and provides a basis for genetic diagnosis and counseling. [Extracted from the article]