In analbuminemia, a very rare inherited syndrome, subjects produce little or no albumin (1/100th to 1/1000th normal), presumably because of a mutation in the albumin gene; yet, they have only moderate edema and few related symptoms owing to a compensatory increase in other plasma proteins. Because of the virtual absence of albumin the defect must be identified at the DNA level. In this study the mutation causing analbuminemia in an Italian family was investigated by analysis of DNA from a mother and her daughter. The mother was homozygous for the trait and had a serum albumin value of <0.01 g/dl (about 1/500th normal); the daughter was heterozygous for the trait and had a nearly normal albumin value. Molecular cloning and sequence analysis of DNA from both mother and daughter showed that the mutation is caused by a nucleotide insertion in exon 8; this produces a frameshift leading to a premature stop, seven codons downstream. The methods of heteroduplex hybridization and single-strand conformation polymorphism were used to compare the DNA of the mother and daughter to the DNA of two unrelated analbuminemic individuals (one Italian and one American). This showed that all three analbuminemic individuals had different mutations; these also differed from the mutation in the only human case previously studied at the DNA level, which was a splicing defect affecting the ligation of the exon 6-exon 7 sequences. Thus, analbuminemia may result from a variety of mutations and is genetically heterogeneous.Serum albumin is the most abundant secreted protein in the body; it comprises about 50%o of the total protein in serum where it has a normal concentration of 3.5-4.5 g/dl (1

Analbuminemia is a very rare recessive disorder in which subjects have little or no circulating albumin, although albumin is normally the most abundant plasma protein and has many functions. Analbuminemla is caused by a variety of mutations in the albumin gene and is exhibited only by subjects homozygous for the defect. Previously the mutation had been identified at the molecular level in only two human cases; in one case it resulted from an exon-splicing defect, and in the other case it was caused by a nucleotide insertion that caused a frameshift and premature stop codon. In this investigation we identified the mutations in three unrelated subjects from different countries. In each instance a single-nucleotide mutation produced a stop codon, but the mutations occurred at three different sites: (i) in an Italian male a C -> T transition at nt 2368 in the genomic sequence of albumin, (u) a C -. T transition at nt 4446 for an American female, and (iU) a G -+ A transition at nt 7708 in a Canadian male. The size of the albumin fragment that might have been produced for the three cases varied from 31-to 213-amino acid residues, but no evidence for a circulating albumin fragment was obtained. The paradox is that analbuminea is extremely rare (frequency <

An electrophoretically slow albumin variant was detected with a phenotype frequency of about 1:1000 in Sweden and was also found in a family of Scottish descent from Kaikoura, New Zealand, and in five families in Tradate, Italy.Structural study established that the major variant component was arginyl-albumin, in which arginine at the -1 position of the propeptide is still attached to the processed albumin. A minor component with the amino-terminal sequence of proalbumin was also present as 3-6% of the total albumin. After amplification ofthe gene segment encoding the prepro sequence of albumin, specific hybridization of DNA to an oligonudeotide probe encoding cysteine at position -2 indicated the mutation of arginine at the -2 position to cysteine (-2 Argm-Cys). This produced the propeptide sequence Arg-Gly-Val-Phe-Cys-Arg. This was confirmed by sequence analysis after pyridylethylation of the cysteine. This mutation produces an alternate signal peptidase cleavage site in the variant proalbumin precursor of arginyl-albumin giving rise to two possible products, arginylalbumin and the variant proalbumin. Another plasma from Bremen had an alloalbumin with a previously described substitution (1 Asp-* Val), which also affects propeptide cleavage.Hypermutability oftwo CpG dinucleotides in the codons for the diarginyl sequence may account for the frequency of mutations in the propeptide. Mutation at these two sites results in a series of recurrent proalbumin variants that have arisen independently in diverse populations.Many rare genetic variants of human serum albumin (alloalbumins) have recently been studied because of interest in their population distribution, site of mutation, and structural change (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16). Three types of alloalbumins have been identified: (i) more than 20 different point mutants that have a single substitution in the mature processed albumin molecule, which contains 585 amino acid residues (for a list with references see ref. 1); (ii) several carboxyl-terminal variants (9, 10); and (iii) a series ofproalbumins (11-16). A proalbumin is a serum albumin molecule that retains a basic aminoterminal hexapeptide because of incomplete post-translational processing. During the second stage of processing in liver a Ca2+-dependent diarginyl-specific proalbumin "convertase" removes the normal propeptide Arg-Gly-ValPhe-Arg-Arg; then the mature albumin with the aminoterminal sequence Asp-Ala-His-Lys-is secreted into the circulation. Proalbumins are characterized by their slower electrophoretic mobility and reduced binding of 63Ni2+ compared to normal (common) albumin A (12,13,15).A number of specific point mutations in or near the propeptide that affect the processing of proalbumins have been identified and have proved useful for study of the

At least 35 allelic variants of human serum albumin have been sequenced at the protein level. All except two COOH-terminal variants, Catania and Venezia, are readily explainable as single-point substitutions. The two chain-termination variants are clustered in certain locations in Italy and are found in numerous unrelated individuals. In order to correlate the protein change in these variants with the corresponding DNA mutation, the two variant albumin genes have been cloned, sequenced, and compared to normal albumin genomic DNA. In the Catania variant, a single base deletion and subsequent frameshift leads to a shortened and altered COOH terminus. Albumin Venezia is caused by a mutation that alters the first consensus nucleotide of the 5' donor splice junction of intron 14 and the 3' end of exon 14, which is shortened from 68 to 43 base pairs. This change leads to an exon skipping event resulting in direct splicing of exon 13 to exon 15. The predicted Venezia albumin product has a truncated amino acid sequence (580 residues instead of 585), and the COOHterminal sequence is altered after Glu-571. The variant COOH terminus ends with the dibasic sequence Arg-Lys that is apparently removed through stepwise cleavage by serum carboxypeptidase B to yield several forms of circulating albumin.

Of the >50 different genetic variants of human serum albumin (afloalbumins) (1-3, 12, 19), many alloalbumins appear to be unique to a particular ethnic group (i-3, 13, 14, 20