A 35 year old woman presents with a tingling sensation in both hands and feet for 2 months, in association with worsening numbness. No other symptoms were present.

Her medical and surgical histories are unremarkable, while her family history is only significant for a brother who died in childhood from Menkes disease.

Currently, she is not on any medications. She is a strict vegan, and does not drink or smoke.

A complete blood count is significant for a Hb of 9.3 g/dL, erythrocyte count of 3.1× 10^12/L, and a MCV of 126 fL. A fasting plasma glucose level is 84 mg/dL.