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Hereditary transthyretin amyloidosis (aTTR; MIM 105210) is an autosomal dominant condition characterized by the progressive buildup of abnormal deposits of amyloid protein (amyloidosis) in the body's organs and tissues, most commonly in the peripheral nervous system. Hereditary aTTR amyloidosis is caused by mutations in the TTR (NM_000371.4) gene and usually begins in the third to fifth decade of life. Hereditary aTTR amyloidosis can lead to peripheral neuropathy and impairment of the autonomic nervous system, and may also affect the heart, kidneys, eyes, and gastrointestinal tract. Individuals with cardiac amyloidosis present with arrhythmia, progressive cardiomyopathy, or orthostatic hypotension, and occasionally mild peripheral neuropathy. Individuals with leptomeningeal amyloidosis may have the following CNS findings: dementia, psychosis, visual impairment, headache, seizures, motor paresis, ataxia, myelopathy, hydrocephalus, or intracranial hemorrhage. The diagnosis of hereditary aTTR amyloidosis is established based on characteristic clinical features, amyloid deposits identified on biopsy that bind to anti-TTR antibodies, and identification of a heterozygous mutation in TTR by molecular genetic testing.