American Journal of Medical Genetics 128A:190–194 (2004) Clinical Report A Severe Form of Amyloidotic Polyneuropathy in a Costa Rican Family With a Rare Transthyretin Mutation (Glu54Lys) Andreas Busse, 1 * Marı ´a A. Sa ´ nchez, 2 Victoria Monterroso, 3 Marco V. Alvarado, 4 and Pedro Leo ´n 1,4 1 Cell and Molecular Biology Research Center (CIBCM), University of Costa Rica, Costa Rica 2 School of Microbiology, University of Costa Rica, Costa Rica 3 Department of Anatomic Pathology, Hospital Mexico, National Social Security System Costa Rica (CCSS), Costa Rica 4 School of Medicine, University of Costa Rica, Costa Rica Four affected siblings in a Costa Rican family presented an aggressive polyneuropathy with widespread involvement of many visceral organs and onset during the third decade of life with rapid loss of muscle mass in the lower limbs and severe dysautonomy. The medical histories include vitreous opacity, cardiac enlargement, dermal and gastrointestinal infiltration, and autonomic dysfunction including circulatory compromise and gastrointestinal disturbances. Histological studies using Congo red stain and immunohistochemical assays with antibodies against the transthyretin (TTR) protein showed widespread deposition of amyloid in extracellular areas, including dermis and gastrointestinal lamina propia, endo- and perineural spaces, and vascular walls. A mutation search in the trans- thyretin (ttr) gene was performed seeking the cause of this severe form of familial amyloido- tic polyneuropathy (FAP). We applied single- stranded conformational polymorphism (SSCP)- analyses followed by sequencing of the four exons of the ttr gene, revealing a point mutation in exon 3, a G to A transition that causes a Glu54Lys codon change. Western blots of plasma proteins incu- bated with anti-transthyretin antibodies after gel electrophoresis provided separation of wild- type and mutant TTR protein in affected family members. ß 2004 Wiley-Liss, Inc. KEY WORDS: familial amiloidosis; transthyre- tin; point mutation; Costa Rica INTRODUCTION Familial amyloidotic polyneuropathy (FAP) is a systemic disease with a generalized and progressive alteration of many tissues and organ types and an autosomal dominant pattern of inheritance. It is known to be clinically and genetically heterogeneous [Kisilevsky and Young, 1996; McKusick, 2003], with many different proteins capable of forming insoluble amyloid precipitates [Bucciantini et al., 2002]. All types of amyloidosis apparently result from proteins or peptides capable of forming beta-pleated sheets that precipitate in the extracellular matrix, often associated to basal laminas [Kisi- levsky and Young, 1996]. Amyloid deposits trigger a sequence of similar pathologic events. Beside direct damages of the target organs leading to tissue disorganization and physiologic dysfunction, complement activation presumably contributes to axon injury in the vicinity of amyloid plaques [Hafer-Macko et al., 2000]. Most FAP cases have been linked to single point mutations in the plasma transporter protein transthyretin, initially described as a prealbumin (OMIM 176300). Today more than 80 mutations in the ttr gene are known, including a few non- amyloidogenic variants [Connors et al., 2000]; the vast majority of ttr mutations are associated with a clinical phenotype. The most frequent type causes a substitution of methionine for valine at position 30 (Val30Met) in the TTR protein, resulting in the classic Swedish-Portuguese-Japanese FAP (Andrade or Portuguese type, OMIM 176300.0001). Different ttr mutations result in different phenotypes, from milder types promoting amyloid deposition in restricted tissues, as the carpal tunnel syndrome (OMIM 176300.0033) reported by Murakami et al. [1994], to more aggressive types that favor the generalized formation of amyloid in many tissues, with the concomitant loss of many normal functions. Even wild-type TTR can give rise to amyloid deposits as is the case in senile systemic amyloidosis [Christmanson et al., 1991]. Yazaki et al. [2000] found a 1:1 ratio of wild-type to variant TTR in amyloid fibrils of the myocardium in five patients with cardiac amyloidosis in FAP with different TTR mutations, while a sixth patient had 80% of wild-type TTR in his cardiac amyloid. This patient had undergone a liver transplantation, which remains the only cure for FAP, but in his case cardiac amyloidosis was not cured by the transplant. On the other hand, McCutchen et al. [1995] described a stabilizing TTR- variant. They showed the Thr119Met nonpathogenic variant to be more stable toward acid denaturation (lysosomal conditions) than wild-type TTR, which in turn is more amyloidogenic. For this reason the double mutant Val30Met/ Thr119Met is protected against the classically severe FAP pathology. Another TTR variant, less protective but still with stabilizing effect on the tetrameric structure is the TTR Arg104His variant, but a compound heterozygotic patient (Val30Met/Arg104His) still presented a very mild form of FAP [Almeida et al., 2000]. Here, we report on the identification of the first FAP case in Costa Rica, a point mutation that substitutes a lysine for a Grant sponsor: The Foundation CR-USA; Grant sponsor: Vice Rectory for Research. *Correspondence to: Andreas Busse, Centro de Investigacio ´ n en Biologı ´a Celular y Molecular (CIBCM), Ciudad de Investigacio ´n, Universidad de Costa Rica, San Pedro, San Jose ´, Costa Rica. E-mail: busseandreas@hotmail.com; pela@conare.ac.cr Received 9 May 2003; Accepted 13 October 2003 DOI 10.1002/ajmg.a.30007 ß 2004 Wiley-Liss, Inc.