Margaret R. Wallace

Biochemical and molecular genetic characterization of a new variant prealbumin associated with hereditary amyloidosis.

Familial amyloidotic polyneuropathy (FAP) is an autosomal dominant late-onset disorder characterized by the extracellular deposition of amyloid fibrils. In all cases studied these fibrils have been found to be composed of plasma prealbumin (transthyretin) containing a single amino acid substitution. Biochemical studies were conducted on amyloid from one patient and plasma prealbumin from his affected brother, both part of a large kindred from the Appalachian region of the United States. Sequence analysis of the amyloid subunit protein showed it to be prealbumin with about two-thirds of the molecules containing a substitution of alanine for threonine at position 60. Studies of the plasma prealbumin showed that the same substitution was present in 40-45% of the protein. Based on this substitution and the prealbumin cDNA sequence, a Pvu II restriction fragment length DNA polymorphism (RFLP) was predicted and demonstrated in DNA of both patients as well as other family members. This RFLP confirms the predicted DNA mutation responsible for the protein variant, and represents an accurate method for detection of this gene.

Genetic linkage map of human chromosome 21

Two of the most common disorders affecting the human nervous system, Down syndrome and Alzheimers disease, involve genes residing on human chromosome 21. A genetic linkage map of human chromosome 21 has been constructed using 13 anonymous DNA markers and cDNAs encoding the genes for superoxide dismutase 1 (SOD1) and the precursor of Alzheimers amyloid beta peptide (APP). Segregation of restriction fragment length polymorphisms (RFLPs) for these genes and DNA markers was traced in a large Venezuelan kindred established as a reference pedigree for human linkage analysis. The 15 loci form a single linkage group spanning 81 cM on the long arm of chromosome 21, with a markedly increased frequency of recombination occurring toward the telomere. Consequently, 40% of the genetic length of the long arm corresponds to less than 10% of its cytogenetic length, represented by the terminal half of 21q22.3. Females displayed greater recombination than males throughout the linkage group, with the difference being most striking for markers just below the centromere. Definition of the linkage relationships for these chromosome 21 markers will help refine the map position of the familial Alzheimers disease gene and facilitate investigation of the role of recombination in nondisjunction associated with Down syndrome.

Localization of the human prealbumin gene to chromosome 18

A human liver cDNA library was screened using an oligonucleotide probe based on the amino acid sequence of human prealbumin. The cDNA insert of one positive clone was sequenced and found to contain the entire coding sequence of human prealbumin plus untranslated 5 and 3 regions. This cDNA was used to probe DNA from a panel of mouse/human somatic cell hybrids. Only those hybrids containing human chromosome 18 showed the human-specific hybridization pattern, thereby localizing the human prealbumin gene to this chromosome.

Identification of a new hereditary amyloidosis prealbumin variant, Tyr-77, and detection of the gene by DNA analysis.

In the last several years, five human plasma prealbumin (transthyretin) variants have been discovered in association with hereditary amyloidosis, a late-onset fatal disorder. We recently studied a patient of German descent with peripheral neuropathy and bowel dysfunction. Biopsied rectal tissue contained amyloid that stained with anti-human prealbumin. Amino acid sequence analysis of the patients plasma prealbumin revealed both normal and variant prealbumin molecules, with the variant containing a tyrosine at position 77 instead of serine. We predicted a single nucleotide change in codon 77 of the variant prealbumin gene, which we then detected in the patients DNA using the restriction enzyme SspI and a specifically tailored genomic prealbumin probe. DNA tests of other family members identified several gene carriers. This is the sixth prealbumin variant implicated in amyloidosis, and adds to the accumulating evidence that the prealbumin amyloidoses are more varied and prevalent than previously thought.

Late‐onset familial amyloid polyneuropathy in an American family of English origin

Recent advances permit biochemical and genetic classification of familial amyloidotic polyneuropathy. We report a family with the methio-nine-30 prealbumin variant, which is atypical in late age of onset and the appearance of proximal arm weakness before more typical generalized neuropathy.

Studies of a DNA marker (G8) genetically linked to Huntington disease in British families.

SummaryClose genetic linkage has been shown between the DNA sequence G8 (locus D4S10) and 16 British families with Huntington disease using the HindIII, EcoR1, Nci1, and Pst1 polymorphisms detected by G8, and by combining all the polymorphisms to give a combined haplotype. Two recombinants have been detected in these families giving a maximum lod score of 17.60 at a Θ of 0.02. These results confirm the originally reported linkage between the loci and provide evidence against significant multilocus heterogeneity for Huntington disease.

DNA Tests for Four Prealbumin Mutations in Hereditary Amyloidosis

A number of variant prealbumin (transthyretin) proteins with single amino acid substitutions have been found to be associated with systemic autosomal dominant amyloidosis. One variant described in Portuguese, Japanese, Swedish and other kindreds contains a methionine at position 30 (Met-30). Another form described in a Jewish patient has an isoleucine at position 33 (Ile-33). The Appalachian form contains an alanine at position 60 (Ala-60). Another kindred that is of German origin has been found with a tyrosine at position 77 (Tyr-77), and the Indiana/Swiss amyloidosis has a serine at position 84 (Ser-84). Point mutations in the prealbumin gene have been predicted for each form, and all five of these single base changes theoretically create new sites for specific restriction enzymes.