MTHFR Deficiency Diagnosis and Treatment
The latest diagnostic techniques used to identify a deficiency in
MTHFR begin with a simple test of homocysteine concentrations in plasma
from either whole blood samples or “total homocysteine measurement in
cell free amniotic fluid is also possible,” (Fowler, B. &
C., 1998). It can be measured using conventional amino acid
chromatography or more commonly in recent times, by a radioenzymatic
method that determines total homocysteine levels, including free,
protein-bound, reduced, and oxidized forms (Tonetti et al
the homocysteine levels are determined to be elevated (although
typically, there should not be any present), a direct assay of
fibroblasts and/or blood cells is done to determine the specific
activity level of MTHFR as previously described by Kutzbach &
Stokstad (1971). If the MTHFR activity level is found to be abnormally
low, then DNA is first isolated from cultured fibroblasts to do the
mutation analysis. Specific mutations can then be determined for certain
exons characterized by Goyette et al (1998) or “by direct sequencing
of the purified PCR fragments” performed by an automatic sequencer
using dye-labeled terminators. “Confirmation of mutations found by
direct sequencing [can be] performed on PCR fragments of different exons
using restriction enzymes,” (Tonetti et al 2000)
such as Hinf I for exon 4, Hha I for exon 6, etc.
“The common MTHFR alleles can be identified by direct sequencing. However, because these alleles create (C677T) or abolish (A1298C) specific restriction sites, they are more commonly identified by first digesting the polymerase chain reaction-amplified genomic DNA with the appropriate restriction enzyme (Hinf I for the C677T allele and Mbo II for the A1298C allele) and then separating the fragments using gel electrophoresis. These procedures have been performed on DNA extracted from many sources, including blood, dried blood spots, and amniotic fluid,” (Botto & Yang, 2000).
It should be noted, however, that diagnosis of severe MTHFR deficiency on the basis of DNA analysis alone is not sufficient. This is because there is no single mutation linked to this severe form of the disease, and thus testing for known mutations may fail to recognize an unknown severe mutation.
Once a diagnosis of MTHFR deficiency is identified, treatment can begin. For mild MTHFR deficiency treatment genereally consists only of diet control and folate supplementation. This is due to previous studies indicating that folates will protect mild MTHFR mutant proteins from losing their FAD, thus restoring enzyme function to near normal levels (Guenther & Sheppard et al, 1999).
Treatment of severe MTHFR deficiency must be more agressive, although even then such treatment is not always effective. Treatment of severe MTHFR deficiency uses a combination of therapies aimed at decreasing homocysteine levels and maximizing any residual enzyme activity. The first line of treatment is the use of folate compounds, including folic or folinic acid (Rosenblatt, 1995). In the body, these compounds work by maximizing residual enzyme activity, reportedly through their ability to protect the enzyme from losing its crucial FAD cofactor (Guenther & Sheppard, et. al, 1999). A second therapy included in treatment of the disorder is methyltetrahydrofolate, which is used to compensate for methylenetetrahydrofolate reductase’s inability to produce this product. Also used in treatment are two compounds aimed at compensating for the low methionine levels that result in MTHFR deficiency: 1) methionine itself, and 2) betaine, a substrate for betaine methyltransferase an enzyme that provides alternate route for conversion of homocysteine to methionine (Figure 1). (Rosenblatt, 1995)