Familial amyloid neuropathy due to transthyretin gene mutations (TTR-FAP) is a rare autosomal dominant inherited disease resulting in the abnormal multi-system deposition of amyloid proteins. These deposits produce a multi-organ disease. AP is usually fatal 10 to 15 years after onset of symptoms if untreated. The prevalence of the disease remains still poorly understood and usually the search for this pathology is done in a third line of investigation. So the average time to diagnosis is extremely long, from 12 to 24 month. Now that the investigators have etiological treatment ( famidis (Vyndaqel®) and Diflunisal (Dolobid)) of this disease, it is essential to be able to detect FAP patients as early as possible. With this study, investigator decided to test for TTR mutation all patients presented with neuropathy of unknown etiology at the first line of investigation. The goal of this study is to evaluate the prevalence of FAP-TTR among neuropathy and defined the best strategy to test this population for TTR mutations.

Inclusion Criteria:

• Adult patient (male and female) aged not more than 90 years old
• Patients with neuropathy identified by EDX exam or small fibre neuropathy identified from a skin biopsy.
• Patients who have undergone the minimal assessment for neuropathy as defined by the HAS (French National Health Authority): biological analysis (fasting glucose, CBC, liver and renal functions, CRP, pituitary TSH)
• Patients belonging to the social security system
• Patient who gave written informed consent

NON-INCLUSION CRITERIA Patients under legal supervision or guardianship Patients with a confirmed documented diagnosis of the cause of neuropathy Patients with evidence of Charcot Marie Tooth neuropathy: very slowly progressive course, pes cavus.

Patients who have already been investigated for a TTR mutation Pregnant women Minors