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J Med Genet 1999;36:629-632 doi:10.1136/jmg.36.8.629
  • Short report

Two pairs of proven monozygotic twins discordant for familial amyloid neuropathy (FAP) TTR Met 30

  1. Miguel Munar-Quésa,
  2. Jorge L Pedrosab,
  3. Teresa Coelhoc,
  4. Leonor Gusmãod,
  5. Raquel Serucad,
  6. António Amorimd,
  7. Jorge Sequeirose
  1. aGrupo de Estudio de la PAF, Palma de Mallorca, Spain, bHospital Oliveira de Azeméis, Portugal, cCentro de Estudos de Paramiloidose, Porto, Portugal, dIPATIMUP, Univ Porto, Portugal, eUnIGENe, IBMC, and ICBAS, Univ Porto, R Campo Alegre 823, 4150 Porto, Portugal
  1. Dr Sequeiros.
  • Received 23 June 1998
  • Revised 24 April 1999

Abstract

Twin studies are an important tool in medical genetics for the evaluation of the relative roles of genetic and non-genetic factors in several diseases. Familial amyloidotic polyneuropathy type I (FAP-I), TTR Met 30, was present in two sets of proven monozygotic (MZ) twins, one from Majorca and the other from Portugal. Monozygosity was established by analysis of DNA polymorphisms. Both pairs were discordant for age at onset and some clinical manifestations of FAP-I. We reviewed the differences in age at onset and clinical features in both sets and in two other pairs of presumed MZ twins with FAP-I and compared them with those in MZ twin pairs with other Mendelian disorders, such as neurofibromatosis type 1, Huntington’s disease, facioscapulohumeral muscular dystrophy, and myotonic dystrophy. We conclude that, in addition to the postulated modifying genes, there must be a significant contribution from non-genetic factors to the phenotypic variability of FAP-I (age at onset and clinical expression), either because of enviromental differences or stochastic events during (or after) the twinning process.

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