In one aspect, the invention provides methods of identifying genetic mutations that are associated with peripheral neurological disease. The methods comprise identifying a difference between a nucleic acid sequence of a small integral protein of the lysosome/late endosome ("SIMPLE") gene from a mammalian subject exhibiting peripheral neuropathy and a nucleic acid sequence of a SIMPLE gene from a subject which is not exhibiting peripheral neuropathy, wherein the difference is a genetic mutation associated with peripheral neurological disease. In another aspect, isolated nucleic acid molecules encoding SIMPLE missense mutations are provided. In another aspect, a method of screening a subject to determine if the subject has a genetic predisposition to develop Charcot-Marie-Tooth type 1C neuropathy is provided. In another aspect, the invention provides kits for determining susceptibility or presence of Charcot-Marie-Tooth type 1C neuropathy in a mammalian subject.