• Vitamin C is an important vitamin. However, it is advised to avoid vitamin C in high doses (Vitamin C has been shown to reduce PMP22 expression by suppressing PMP22 transcription  (sources: https://bestfoot4wardblog.com/2020/02/20/hnpp-the-latest/ and https://n.neurology.org/content/82/10_Supplement/P7.089 -
  Brett Parker, Sezgi Arpag, Raymond Roos, Jun Li  Effect of Ascorbic Acid in Human and Mice with Haploinsufficiency of PMP22 (P7.089), Neurology Journals, April 8, 2014, issue 82, https://doi.org/10.1212/WNL.82.10_supplement.P7.089

• ! You will still need vitamin C!

Following research states that when one has a casein intolerance (protein in cow's milk), that the antibodies in our bodies also attack a protein called MAG (myelin-associated glycoprotein). This protein is either important for the myelin in the central nervous system and for the myelin in the peripheral nervous system. Although this is a recent finding, and this hasn't been tested for HNPP, it might be worth to replace cow's milk for a few weeks in order to find out if this makes a difference. There are a lot of alternatives. Please check with a medical professional if you want to replace cow's milk.

Source: https://www.pnas.org/doi/10.1073/pnas.2117034119 Chunder R, Weier A, Mäurer H, Luber N, Enders M, Luber G, Heider T, Spitzer A, Tacke S, Becker-Gotot J, Kurts C, Iyer R, Ho PP, Robinson WH, Lanz TV, Kuerten S. Antibody cross-reactivity between casein and myelin-associated glycoprotein results in central nervous system demyelination. Proc Natl Acad Sci U S A. 2022 Mar 8;119(10):e2117034119. doi: 10.1073/pnas.2117034119. Epub 2022 Mar 2. PMID: 35235454; PMCID: PMC8916005.

To be avoided in high doses

(source: CMTA USA: https://www.facebook.com/CMTAssociation/posts/did-you-know-megadoses-of-vitamin-b6-pyridoxine-are-potentially-harmful-for-peop/565928290093996/)