Aquaporin 3 is found in "normal skeletal myofibres" (2).

I suspect it will be found that the problem is not a mutation, but something interfering with the normal proper function of the aqp3 channels.

Aquaporin 3 is, in addition to being a water channel, also an arsenic transporter.

Arsenic has been implicated in Alzheimer's in at least a few instances. For example, this statement appears in Reference 3 below:

"Arsenic can induce apoptosis in cortical neurons of rats. This process is based on the activation of JNK3 and p38 MAPK by arsenic...[which] can activate p38 MAPK and JNK3...."

And the title of the last paper speaks for itself: “Arsenic exposure may be a risk factor for Alzheimer's disease.”

References:
1. Mulders SM, Olde Weghuis D, van Boxtel JA, van Kessel AG, Echevarria M, van Os CH, Deen PM. Localization of the human gene for aquaporin 3 (AQP3) to chromosome 9, region p21-->p12, using fluorescent in situ hybridization. Cytogenet Cell Genet. 1996;72(4):303-5. Abstract

2. Wakayama Y, Jimi T, Inoue M, Kojima H, Shibuya S, Murahashi M, Hara H, Oniki H. Expression of aquaporin 3 and its localization in normal skeletal myofibres. Histochem J. 2002 Jun-Jul;34(6-7):331-7. Abstract

3. Baum L, Chan IH, Cheung SK, Goggins WB, Mok V, Lam L, Leung V, Hui E, Ng C, Woo J, Chiu HF, Zee BC, Cheng W, Chan MH, Szeto S, Lui V, Tsoh J, Bush AI, Lam CW, Kwok T. Serum zinc is decreased in Alzheimer's disease and serum arsenic correlates positively with cognitive ability. Biometals. 2010 Feb;23(1):173-9. Abstract

4. Gharibzadeh S, Hoseini SS. Arsenic exposure may be a risk factor for Alzheimer's disease. J Neuropsychiatry Clin Neurosci. 2008 Fall;20(4):501. Abstract

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