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.
The two most problematic mutations that can occur are C677T and A1298C, which denote the placement of the mutation on the gene. 1  The most common forms of MTHFR mutation involve various combinations of these genes being passed on from each parent: 1  Homozygous: the same gene passed on from both parents- can occur if both pass on the 677 mutation, or the 1298 mutation.