In 2005, about 20 percent (82,600 million gallons per day (Mgal/d)) of total national water withdrawals (about 410,000 Mgal/d) came from groundwater sources. (All 2010 water use information is from the report Estimated use of water in the United States in 2010.) Very little saline groundwater was used in 2005.
The MTHFR nucleotide at position 677 in the gene has two possibilities: C (cytosine) or T (thymine). C at position 677 (leading to an alanine at amino acid 222) is the normal allele. The 677T allele (leading to a valine substitution at amino acid 222) encodes a thermolabile enzyme with reduced activity.
If the MTHFR mutation test is negative, then the C677T and A1298C mutations were not detected and the tested person's elevated homocysteine level is likely due to another cause. Other, more rare MTHFR genetic mutations will not be detected with typical testing.t may be ordered if a person has a close relative with known MTHFR genetic mutations, particularly if that person also has elevated homocysteine levels. MTHFR C677T and A1298C gene mutations are the most common and the ones that are typically tested.