Phenylalanine is also needed to produce both of the thyroid hormones,
so we would expect MS patients to have an increased risk of developing hypothyroidism. The following study on MS and thyroid disorders found
that thyroid disorders were at least three times more common in women
with MS than in female controls, and that, this was accounted for mainly
by the prevalence of hypothyroidism.

Association of MS with Thyroid Disorders.
Karni, A., O. Abramsky. 1999. Neurology 53(4):883-5.