A case of familial transthyretin amyloidosis with TTR Cys 114 gene polymorphism is described (first in Russia and third in the world). The clinical picture of the proband was dominated by symptoms of autonomous polyneuropathy (orthostatic hypotension, erectile dysfunction, diarrhea, tachycardia, foot dyshydrosis) and of somatic nerve lesions (dumbness, impaired surface and deep sensitivity in the limbs). The patient presented with vitreous body opacity, disturbed eye movements, lateralized sensory symptoms, and difficulty of speech (baryphonia). Electromyographic quantitative autonomous testing and measurement of evoked sympathetic skin potentials confirmed affection of peripheral nerves. Heart ultrasound revealed restrictive amyloid cardiopathy. Histological analysis showed amyloid deposition in the intestines and sural nerve. The proband, his daughter, brother (monozygous twin), and brother's daughter had mutant TTR Cys 114 gene. The brother also had amyloid deposits in the absence of clinical signs of the disease. Analysis of familial medical history demonstrated autosomal dominant inheritance of this mutation in 4 generations. Its possible origin and clinical features of the disease are discussed.