Homocystinuria due to MTHFR deficiency

Homocystinuria is an inherited pathology that affects homocysteine metabolism and has an autosomal recessive pattern. Homocysteine is an essential amino acid for cell and tissue growth.

This metabolism defect is mainly due to deficiency of the enzyme cystathionine beta synthase or CBS, which is known as classical homocystinuria, but there are other genetic disorders that affect homocysteine metabolism such as homocystinuria due to MTHFR deficiency and methylmalonic acidemia type cblC, cblD, and cblD.  

In homocystinuria due to MTHFR deficiency, MTHFR refers to the gene involved in the development of the pathology which is located on chromosome 1p36.3 and codes for the enzyme 5, 10 methylenetetrahydrofolate reductase. Some mutations in this gene alter the function of the enzyme, inactivating it and initiating the development of the disease.

Homocystinuria can occur when the body does not produce enough of the MTHFR enzyme or the one produced is not functional. The main function of the MTHFR enzyme is to catalyze the conversion of homocysteine to methionine, two highly relevant amino acids.

Therefore, when this occurs, as it does during the course of this pathology, there is an increase in homocysteine levels and a decrease in methionine levels in blood and urine, which in turn triggers the development of the characteristic clinical picture of the disease.


Homocystinuria due to MTHFR deficiency results in a multisystem disorder affecting connective tissue, muscles, central nervous system (CNS), and cardiovascular system, leading to signs and symptoms that may appear in the first year of life as apnea, microcephaly and seizures, or in adulthood, in which mainly cognitive impairment, psychiatric disorders, and strokes occur.

Elevated plasma homocysteine levels may also be due to other causes such as nutritional deficiencies of vitamin cofactors, certain medications or the presence of other conditions. Other factors associated with increased homocysteine are age, male sex, smoking, coffee consumption, high blood pressure, unfavorable lipid profile, elevated creatinine and poor diet.


Treatment with a special diet and drugs can prevent the development of the complications mentioned previously, but it must be started in the first years of life to be truly effective. Therefore, it is crucial to study and know the predisposition to develop the disease.

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