Analbuminemia in a Slovak Romany (gypsy) family: case report and mutational analysis

Performance evaluation of different albumin assays for the detection of analbuminemia

Analbuminemia is characterized by the near absence of albumin in the plasma. Different methods are available for measuring albumin levels, but they do not necessarily agree with one another. It is a concern that analbuminemic samples could be falsely characterized due to the incorrect estimation of albumin. The objective of the work was to evaluate the performance of different assays in detecting analbuminemia. Albumin knockout (Alb-/-) mouse plasma was used to test the suitability of different albumin assays for their ability to properly characterize extreme albumin deficiency. Bromocresol green (BCG), bromocresol purple (BCP), enzyme-linked immunosorbent assay (ELISA), liquid chromatography-tandem mass spectrometry (LC-MS/MS), and gel electrophoresis were tested. The LC-MS/MS assay exhibited broad coverage of the amino acid sequence of albumin and indicated 8,400-fold lower (P<0.0001) albumin expression in Alb-/- than wildtype (WT), demonstrating its suitability for identifying extreme albumin deficiency. ELISA estimated albumin at 1.5±0.1 g/dL in WT and was below the detection limit in all Alb-/- samples. Gel electrophoresis yielded consistent results with LC-MS/MS and ELISA. The BCG assay overestimated albumin with apparently appreciable albumin concentrations in Alb-/- mice, yet the assay still indicated a significant difference between genotypes (Alb-/-, 1.2±0.05 g/dL, WT, 3.7±0.1 g/dL, P<0.0001). BCP drastically overestimated albumin and could not successfully identify the known analbuminemic phenotype of Alb-/- mice. By using Alb-/- plasma as a reference material and LC-MS/MS as a reference method, ELISA and gel electrophoresis appear appropriate for identifying analbuminemia, while BCG and BCP are not suitable. It is concluded that dye-binding assays should be avoided when extreme hypoalbuminemia or analbuminemia is suspected.

Alterations in the Plasma Protein Expression Pattern in Congenital Analbuminemia—A Systematic Review

Albumin is a highly abundant plasma protein with multiple functions, including the balance of fluid between body compartments and fatty acid trafficking. Humans with congenital analbuminemia (CAA) do not express albumin due to homozygosity for albumin gene mutation. Lessons about physiological control could be learned from CAA. Remarkably, these patients exhibit an apparently normal lifespan, without substantial impairments in physical functionality. There was speculation that tolerance to albumin deficiency would be characterized by significant upregulation of other plasma proteins to compensate for analbuminemia. It is unknown but possible that changes in plasma protein expression observed in CAA are required for the well-documented survival and general wellness. A systematic review of published case reports was performed to assess plasma protein pattern remodeling in CAA patients who were free of other illnesses that would confound interpretation. From a literature search in Pubmed, Scopus, and Purdue Libraries (updated October 2022), concentration of individual plasma proteins and protein classes were assessed. Total plasma protein concentration was below the reference range in the vast majority of CAA patients in the analysis, as upregulation of other proteins was not sufficient to prevent the decline of total plasma protein when albumin was absent. Nonetheless, an impressive level of evidence in the literature indicated upregulated plasma levels of multiple globulin classes and various specific proteins which may have metabolic functions in common with albumin. The potential role of this altered plasma protein expression pattern in CAA is discussed, and the findings may have implications for other populations with hypoalbuminemia.

Congenital analbuminaemia: molecular defects and biochemical and clinical aspects

BACKGROUND

DNA and mRNA sequencing of the coding regions of the human albumin gene (ALB) and of its intron/exon junctions has revealed twenty-one different molecular defects causing congenital analbuminaemia (CAA).

SCOPE OF REVIEW

To describe the mutations in molecular terms and to present the current knowledge about the most important biochemical and clinical effects of CAA.

MAJOR CONCLUSIONS

CAA is rare, but its frequency seems to be significantly higher in restricted and minimally admixed populations. The condition affects especially the lipid metabolism but apart from a possible increased risk for atherosclerotic complications, it is generally associated with mild clinical symptoms in adults. By contrast, several reports indicate that analbuminaemic individuals may be at risk during the perinatal and childhood periods, in which they seem to show increased morbidity and mortality. The twenty-one causative defects include seven nonsense mutations, seven changes affecting splicing, five frame-shift/deletions, one frame-shift/insertion and one mutation in the start codon. These results indicate that the trait is an allelic heterogeneous disorder caused by homozygous (nineteen cases) or compound heterozygous (single case) inheritance of defects. Most mutations are unique, but one, named Kayseri, is responsible for about half of the known cases.

GENERAL SIGNIFICANCE

Study of the defects in the ALB resulting in CAA allows the identification of "hot spot" regions and contributes to understanding the molecular mechanism underlying the trait. Such studies could also give molecular information about different aspects of ALB regulation and shed light on the regulatory mechanisms involved in the synthesis of the protein. This article is part of a Special Issue entitled Serum Albumin.

A novel splicing mutation causes analbuminemia in a Portuguese boy

Analbuminemia is a rare autosomal recessive disorder manifested by the absence or severe reduction of circulating serum albumin in homozygous or compound heterozygous subjects. It is an allelic heterogeneous defect, caused by a variety of mutations within the albumin gene. The analbuminemic condition was suspected in a Portuguese boy who presented with low albumin level (about 3.8 g/L) and a significant hypercholesterolemia, but with no clinical findings. The albumin gene was screened by single strand conformational polymorphism and heteroduplex analysis and submitted to direct DNA sequencing. The proband was found to be homozygous for a previously unreported G>A change at position c.1289+1, the first base of intron 10, which inactivates the strongly conserved GT dinucleotide at the 5' splice site consensus sequence of the intron. The effect of this mutation was evaluated by examining the cDNA obtained by RT-PCR from the albumin mRNA extracted from proband's leukocytes. The splicing defect results in the skipping of the preceding exon. The subsequent reading frame-shift in exon 11 produces a premature stop codon located 33 codons downstream the 5' end of the exon. This extensive cDNA alteration is responsible for the analbuminemic trait. Both parents were found to be heterozygous for the same mutation. DNA and cDNA sequence analysis established the diagnosis of congenital analbuminemia in the proband. The effects of the so far identified splice-site mutations in the albumin gene are discussed.

Congenital analbuminemia with acute glomerulonephritis: a diagnostic challenge

Congenital analbuminemia is a rare autosomal recessive disease in which albumin is not synthesized. Patients with this disorder generally have minimal symptoms despite complete absence of the most abundant serum protein. We report a family in which the proband presented with acute glomerulonephritis and was found to have underlying congenital analbuminemia. Consequently, the patient's two older sisters were diagnosed with the same condition. Sequencing of the human serum albumin gene was performed, and a homozygous mutation in exon 3 was found in all three patients. Together with these three patients of Arab ethnicity, this mutation, known as Kayseri, is the most frequently described mutation in congenital analbuminemia. This article discusses clinical features and diagnostic challenges of this disorder, particularly in this case, where concomitant renal disease was present.

Mutations and polymorphisms of the gene of the major human blood protein, serum albumin

We have tabulated the 77 currently known mutations of the familiar human blood protein, serum albumin (ALB). A total of 65 mutations result in bisalbuminemia. Physiological and structural effects of these mutations are included where observed. Most of the changes are benign. The majority of them were detected upon clinical electrophoretic studies, as a result of a point mutation of a charged amino acid residue. Three were discovered by their strong binding of thyroxine or triiodothyronine. A total of 12 of the tabulated mutations result in analbuminemia, defined as a serum albumin concentration of <1 g/L. These were generally detected upon finding a low albumin concentration in patients with mild edema, and involve either splicing errors negating translation or premature stop codons producing truncated albumin molecules. A total of nine mutations, five of those with analbuminemia and four resulting in variants modified near the C-terminal end, cause frameshifts. Allotypes from three of the point mutations become N-glycosylated and one C-terminal frameshift mutation shows O-glycosylation.

Analbuminemia in a Swedish male is caused by the Kayseri mutation (c228_229delAT)

BACKGROUND

Analbuminemia is a rare autosomal recessive disorder manifested by the absence, or severe reduction, of circulating serum albumin. Here we report the first case of hereditary analbuminemia in the ethnic Swedish population, and we define the molecular defect that causes the analbuminemic trait.

METHODS

Total DNA, extracted from peripheral blood samples from the analbuminemic proband and his parents, was PCR-amplified using oligonucleotide primers designed to amplify the 14 exons, the exon-intron splice junctions, and the 5' and 3' untranslated regions of the albumin gene. The products were screened for mutations by single-strand conformation polymorphism and heteroduplex analyses. The latter allowed the identification of the abnormal fragment, which was then sequenced.

RESULTS

The analbuminemic trait of the proband was caused by a homozygous AT deletion at nucleotides c. 228-229, the 91st and 92nd bases of exon 3. This defect, previously identified as Kayseri mutation [M. Galliano, M. Campagnoli, A. Rossi, et al. Molecular diagnosis of analbuminemia: a novel mutation identified in two Amerindian and two Turkish families. Clin Chem 2002;48: 844-849.], produces a frameshift leading to a premature stop, two codons downstream.

CONCLUSIONS

The Kayseri mutation appears to be the most common cause of analbuminemia in humans, and is found in individuals belonging to geographically distant, and apparently unrelated ethnic groups.