In case this helps...

I discovered by genetic testing that I'm a carrier of the Biotinidase Deficiency variant. This causes me to have very low "normal" values of the enzyme. As best I understand it, the enzyme is responsible for allowing your body to make use of biotin (B7) in food sources. I'm not supposed to affected with just low levels, but since taking biotin supplements, a metabolic problem I was experiencing has disappeared completely. Biotin is involved in the metabolic process involved.

I also took the Nutra Eval test at one point, and it didn't show any problems with my biotin levels. Without high enough levels of this enzyme, though, I think it was indeed impeding my ability to make use of it, and supplements have absolutely helped me.