I think you may have found another family with genetic beriberi--mine.
My toes started the pins-'n-needles thing, got worse...
results of tests: "peripheral neuropathy of moderate severity"
not MS (sister has); not ALS, ...
so I'm part of the 30% with idiopathic neuropathy
B6 level fine, B12 high, B1 not detectable!
Might explain my mother having increasingly weak legs--and me, too.
Father had an enlarged heart (another symptom)--and me, too.
Inherited from both??? or merely coincidence.
Father did have a severe tremor and, wow, do I have an intentional tremor--
but that's not part of not absorbing thiamine.
Anyway, if you want to talk..