Genetic expression of a transthyretin mutation in typical and late‐onset Portuguese families with familial amyloidotic polyneuropathy

Two studies were conducted to explore questions concerning the expression of a mutant transthyretin (TTR) gene, found in Portuguese patients with familial amyloidotic polyneuropathy (FAP). In a kindred with typical onset of the disease, complete agreement between genotype and phenotype was seen for all carriers of the variant TTR with a methionine-for-valine substitution at position 30 (TTR[Met³⁰]). In another study involving a FAP kindred with a late onset of clinical disease, TTR(Met³⁰) was found in plasma in asymptomatic persons with ages above the usual age of onset of the disease. No evidence was obtained for the existence of a different mutation in TTR or for repression of the expression of the mutant TTR gene in this kindred. The factors responsible for the delay in the development of clinical manifestations in late-onset patients are not known and warrant further study.