Discordant symptoms in monozygotic twins with familial amyloidotic polyneuropathy (FAP) (TTR Met 30)

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Abstract
Two monozygotic twin brothers, 55 years of age, are carriers of the TTR Met 30 gene. Twin no. 1 had onset of typical FAP symptoms seven years ago, while twin no. 2 is absolutely healthy. The twins have the same educational background, are working in the same industry and are living in the same area. The progress of symptoms in twin no. 1 was rather rapid with polyneuropathy, gastrointestinal and heart symptoms. Liver transplantation was per-formed in twin no. 1 in 1993, with a successful result. The discordance of FAP symptoms in identical twins might indicate that environmental factors are of importance for the onset of FAP symptoms. The possible importance of environmental factors is indicated by a population study made in the same area. The TTR Met 30 gene carrier frequency is 1.6 per cent, while the frequency of FAP patients in the same area is only 0.05 per cent, indicating a gene penetrance of only about 5 per cent. To our knowledge this is the first report of discordant symptoms in monozygotic twins with ATTR.