DHFR

Dihydrofolate reductase (DHFR) is an essential enzyme that converts dihydrofolate (DHF) into tetrahydrofolate (THF), a key molecule for DNA synthesis, repair, and methylation reactions. 

Given its central role in cell growth and division, DHFR is a major target of antifolate drugs like methotrexate, and genetic mutations in DHFR can impact folate metabolism, cancer therapy resistance, and neurological health.

What is DHFR?

Dihydrofolate reductase (DHFR) is a gene that codes an essential enzyme that helps convert dihydrofolate (DHF) into tetrahydrofolate (THF), a critical molecule needed for DNA synthesis, repair, and amino acid metabolism. THF is also involved in methylation reactions, which play a role in gene expression and overall cell function. 

Because DHFR is essential for cell growth and division, it is a key target for antifolate drugs like methotrexate (MTX), which are used to treat cancer and autoimmune diseases.

DHFR Deficiency and Clinical Relevance

DHFR deficiency is a rare genetic disorder caused by homozygous DHFR mutations, most notably p.Asp153Val. It leads to megaloblastic anemia and cerebral folate deficiency (CFD). 

The disease manifests in early childhood and worsens without treatment. Folinic acid (5-FTHF) supplementation can reverse anemia and improve neurological symptoms, though epilepsy may persist.

Clinical Scenarios Associated with DHFR Mutations

Several clinical situations may be affected by DHFR mutations:

Megaloblastic Anemia & Neurologic Disease

The p.Asp153Val mutation impairs DHFR function, reducing intracellular folate conversion and leading to megaloblastic anemia and cerebral folate deficiency (CFD), meaning that folate levels in the cerebrospinal fluid (CSF) are dangerously low, even if blood folate levels appear normal.

Various neurological symptoms, such as developmental delays, learning difficulties, and seizures, are associated with DHFR deficiency. 

Genetic testing for DHFR mutations should be considered in patients with macrocytic anemia, unexplained neurological symptoms, and cerebral folate deficiency despite normal plasma folate.

Neural Tube Defects (NTDs)

Some DHFR polymorphisms, including the 19-bp intron 1 deletion, may influence folate metabolism and NTD risk, though evidence remains inconclusive.

Cancer, Autoimmune Conditions & Methotrexate Resistance

DHFR overexpression can promote cancer progression and chemotherapy resistance. 

DHFR is a key target for methotrexate, an antifolate drug used to treat cancer and rheumatoid arthritis by inhibiting DHFR and disrupting DNA synthesis in rapidly dividing cells. However, mutations or structural variations in DHFR can alter enzyme conformation and drug binding, potentially leading to methotrexate resistance.

Specific polymorphisms (C829T, promoter variants) are linked to methotrexate (MTX) resistance in leukemia and autoimmune disease, potentially impacting treatment outcomes in cancer and autoimmune diseases by reducing drug efficacy.

When is DHFR Activity or Related Information Relevant?

A patient's DHFR genetic status may be considered in the following scenarios:

Methotrexate Therapy Management

Since methotrexate interferes with folate metabolism, clinicians monitor related factors to assess its safety and effectiveness. Certain DHFR gene mutations may alter the efficacy of methotrexate, necessitating close monitoring. 

Routine lab tests include:

• Blood counts – to check for bone marrow suppression.
• Liver function tests – to detect potential liver toxicity.
• Kidney function tests – since methotrexate is cleared through the kidneys and can accumulate in cases of kidney dysfunction.

Personalized Methotrexate Dosing (Research)

Emerging research explores how genetic variations in DHFR and other folate metabolism genes impact methotrexate response. These studies aim to develop personalized dosing strategies to maximize effectiveness while minimizing toxicity, particularly in cancer and autoimmune disease treatment.

Clinical Considerations for DHFR Testing

Consider DHFR genetic testing in patients with macrocytic anemia, unexplained neurological symptoms, or cerebral folate deficiency despite normal blood folate.

Test for DHFR polymorphisms in cancer and autoimmune patients with poor methotrexate response to guide alternative treatment strategies.

Initiate folinic acid therapy in confirmed DHFR deficiency to improve anemia and neurological function.

Test Procedure and Interpretation

Testing for DHFR is often performed as a genetic test to look for mutations in the gene that would alter functional protein availability. The following section outlines the testing procedures and interpretation.

Testing Procedure and Preparation

Genetic testing involves blood, saliva, or cheek swab samples, although specialized laboratories may recommend different sample types. 

A cheek swab or saliva sample is easily obtained from the comfort of home, while blood samples typically require a blood draw.

Normal Reference Ranges

Normal reference ranges for DHFR genetic testing are considered to be without mutations that can alter the activity of the DHFR proteins.

Clinical Implications of Positive DHFR Mutations

The clinical implications of a positive DHFR mutation test result will vary by individual, although DHFR mutations in symptomatic patients may signal a need for further assessment and possibly treatment, especially in the setting of various symptoms.

Patients or practitioners with questions about the clinical implications of DHFR mutations should seek further assessment with a genetic counselor or expert. 

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