These factors include. 1  Living at high latitudes (closer to the polar regions), particularly during winter months. 2  Air quality conditions: high levels of air pollution. 3  Weather conditions: dense cloud covering. 4  The degree to which clothing covers the skin. 5  Use of sunscreen. 6  Skin pigmentation: darker skin types.
A few cases of severe homocysteinemia have been due to rare MTHFR gene mutations (sometimes in combination with a second common MTHFR gene mutation). Symptoms in these patients varied greatly but often involved pronounced neurological symptoms and blood vessel disease.
Two copies of A1298C are not typically associated with increased homocysteine levels. 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.