A novel mutation in the albumin gene (c.1A>C) resulting in analbuminemia

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.

Progress and Challenges in the Biology of FNDC5 and Irisin

In 2002, a transmembrane protein-now known as FNDC5-was discovered and shown to be expressed in skeletal muscle, heart, and brain. It was virtually ignored for 10 years, until a study in 2012 proposed that, in response to exercise, the ectodomain of skeletal muscle FNDC5 was cleaved, traveled to white adipose tissue, and induced browning. The wasted energy of this browning raised the possibility that this myokine, named irisin, might mediate some beneficial effects of exercise. Since then, more than 1000 papers have been published exploring the roles of irisin. A major interest has been on adipose tissue and metabolism, following up the major proposal from 2012. Many studies correlating plasma irisin levels with physiological conditions have been questioned for using flawed assays for irisin concentration. However, experiments altering irisin levels by injecting recombinant irisin or by gene knockout are more promising. Recent discoveries have suggested potential roles of irisin in bone remodeling and in the brain, with effects potentially related to Alzheimer's disease. We discuss some discrepancies between research groups and the mechanisms that are yet to be determined. Some important questions raised in the initial discovery of irisin, such as the role of the mutant start codon of human FNDC5 and the mechanism of ectodomain cleavage, remain to be answered. Apart from these specific questions, a promising new tool has been developed-mice with a global or tissue-specific knockout of FNDC5. In this review, we critically examine the current knowledge and delineate potential solutions to resolve existing ambiguities.

Loss of UGP2 in brain leads to a severe epileptic encephalopathy, emphasizing that bi-allelic isoform-specific start-loss mutations of essential genes can cause genetic diseases

Developmental and/or epileptic encephalopathies (DEEs) are a group of devastating genetic disorders, resulting in early-onset, therapy-resistant seizures and developmental delay. Here we report on 22 individuals from 15 families presenting with a severe form of intractable epilepsy, severe developmental delay, progressive microcephaly, visual disturbance and similar minor dysmorphisms. Whole exome sequencing identified a recurrent, homozygous variant (chr2:64083454A > G) in the essential UDP-glucose pyrophosphorylase (UGP2) gene in all probands. This rare variant results in a tolerable Met12Val missense change of the longer UGP2 protein isoform but causes a disruption of the start codon of the shorter isoform, which is predominant in brain. We show that the absence of the shorter isoform leads to a reduction of functional UGP2 enzyme in neural stem cells, leading to altered glycogen metabolism, upregulated unfolded protein response and premature neuronal differentiation, as modeled during pluripotent stem cell differentiation in vitro. In contrast, the complete lack of all UGP2 isoforms leads to differentiation defects in multiple lineages in human cells. Reduced expression of Ugp2a/Ugp2b in vivo in zebrafish mimics visual disturbance and mutant animals show a behavioral phenotype. Our study identifies a recurrent start codon mutation in UGP2 as a cause of a novel autosomal recessive DEE syndrome. Importantly, it also shows that isoform-specific start-loss mutations causing expression loss of a tissue-relevant isoform of an essential protein can cause a genetic disease, even when an organism-wide protein absence is incompatible with life. We provide additional examples where a similar disease mechanism applies.

Diagnosis, Phenotype, and Molecular Genetics of Congenital Analbuminemia

Congenital analbuminemia (CAA) is an inherited, autosomal recessive disorder with an incidence of 1:1,000,000 live birth. Affected individuals have a strongly decreased concentration, or complete absence, of serum albumin. The trait is usually detected by serum protein electrophoresis and immunochemistry techniques. However, due to the existence of other conditions in which the albumin concentrations are very low or null, analysis of the albumin (ALB) gene is necessary for the molecular diagnosis. CAA can lead to serious consequences in the prenatal period, because it can cause miscarriages and preterm birth, which often is due to oligohydramnios and placental abnormalities. Neonatally and in early childhood the trait is a risk factor that can lead to death, mainly from fluid retention and infections in the lower respiratory tract. By contrast, CAA is better tolerated in adulthood. Clinically, in addition to the low level of albumin, the patients almost always have hyperlipidemia, but they usually also have mild oedema, reduced blood pressure and fatigue. The fairly mild symptoms in adulthood are due to compensatory increment of other plasma proteins. The condition is rare; clinically, only about 90 cases have been detected worldwide. Among these, 53 have been studied by sequence analysis of the ALB gene, allowing the identification of 27 different loss of function (LoF) pathogenic variants. These include a variant in the start codon, frame-shift/insertions, frame-shift/deletions, nonsense variants, and variants affecting splicing. Most are unique, peculiar for each affected family, but one, a frame-shift deletion called Kayseri, has been found to cause about one third of the known cases allowing to presume a founder effect. This review provides an overview of the literature about CAA, about supportive and additional physiological and pharmacological information obtained from albumin-deficient mouse and rat models and a complete and up-to-date dataset of the pathogenic variants identified in the ALB gene.

A novel insertion (c.1098dupT) in the albumin gene causes analbuminemia in a consanguineous family

Congenital analbuminemia (OMIM # 616000) is an extremely rare autosomal recessive disorder, caused by variations in the albumin gene (ALB), which is generally thought to be a relatively benign condition in adulthood, but seems to be potentially life threatening in the pre- and peri-natal period. The subject of our study was a consanguineous family, in which we identified two analbuminemic individuals. Mutation analysis of ALB revealed that both are homozygous for a previously unreported insertion in exon 9 (c.1098dupT), causing a subsequent frame-shift with the generation of a premature stop codon, and an aberrant truncated putative protein product, p.Val367fsTer12. This variation is present in heterozygous condition in several other members of the family. The phenotype and the molecular genetics of CAA are discussed.

A nucleotide deletion and frame-shift cause analbuminemia in a Turkish family

Congenital analbuminemia is an autosomal recessive disorder, in which albumin, the major blood protein, is present only in a minute amount. The condition is a rare allelic heterogeneous defect, only about seventy cases have been reported worldwide. To date, more than twenty different mutations within the albumin gene have been found to cause the trait. In our continuing study of the molecular genetics of congenital analbuminemia, we report here the clinical and biochemical findings and the mutation analysis of the gene in two Turkish infants. For the molecular analysis, we used our strategy, based on the screening of the gene by single-strand conformation polymorphism, heteroduplex analysis and direct DNA sequencing. The results showed that both patients are homozygous for the deletion of a cytosine residue in exon 5, in a stretch of four cytosines starting from nucleotide position 524 and ending at position 527 (NM_000477.5(ALB):c.527delC). The subsequent frame-shift inserts a stop codon in position 215, markedly reducing the size of the predicted protein product. The parents are both heterozygous for the same mutation, for which we propose the name Erzurum from the city of origin of the family. In conclusion, our results show that in this family congenital analbuminemia is caused by a novel frame-shift/deletion defect, confirm the inheritance of the trait, and contribute to advance our understanding of the molecular basis underlying this condition.

A novel splicing mutation in the albumin gene (c.270+1G>T) causes analbuminaemia in a German infant

Congenital analbuminaemia is a rare autosomal recessive disorder manifested by the presence of a very low amount of circulating serum albumin. The clinical diagnosis may be challenging because of the absence of unambiguous symptoms and because hypoalbuminemia may have many causes different from a genetic lack of the protein. We describe the clinical and molecular characterization of a new case of congenital analbuminaemia in an infant of apparently non-consanguineous parents from Treves, Germany. For molecular diagnosis, we used our strategy, based on the screening of the albumin gene by single-strand conformation polymorphism, heteroduplex analysis and direct DNA sequencing, which revealed that the proband is homozygous and both parents are heterozygous, for a novel G > T transversion at nucleotide c.270+ 1, the first base of intron 3. The mutation inactivates the strongly conserved GT dinucleotide at the 5' splice site consensus sequence of this intron. In conclusion, we report the clinical findings and the molecular defect of this case, which contributes to a better understanding of the biological mechanism of congenital analbuminaemia.

Variation in genes controlling warfarin disposition and response in American Indian and Alaska Native people: CYP2C9, VKORC1, CYP4F2, CYP4F11, GGCX

OBJECTIVES

Pharmacogenetic testing is projected to improve health outcomes and reduce the cost of care by increasing therapeutic efficacy and minimizing drug toxicity. American Indian and Alaska Native (AI/AN) people historically have been excluded from pharmacogenetic research and its potential benefits, a deficiency we sought to address. The vitamin K antagonist warfarin is prescribed for prevention of thromboembolic events, although its narrow therapeutic index and wide interindividual variability necessitate close monitoring of drug response. Therefore, we were interested in variation in CYP2C9, VKORC1, CYP4F2, CYP4F11, and GGCX, which encode enzymes important for the activity of warfarin and synthesis of vitamin K-dependent blood clotting factors.

METHODS

We resequenced these genes in 188 AI/AN people in partnership with Southcentral Foundation in Anchorage, Alaska and 94 Yup'ik people living in the Yukon-Kuskokwim Delta of southwest Alaska to identify known or novel function-disrupting variation. We conducted genotyping for specific single nucleotide polymorphisms in larger cohorts of each study population (380 and 350, respectively).

RESULTS

We identified high frequencies of the lower-warfarin dose VKORC1 haplotype (-1639G>A and 1173C>T) and the higher-warfarin dose CYP4F2*3 variant. We also identified two relatively common, novel, and potentially function-disrupting variants in CYP2C9 (M1L and N218I), which, along with CYP2C9*3, CYP2C9*2, and CYP2C9*29, predict that a significant proportion of AI/AN people will have decreased CYP2C9 activity.

CONCLUSION

Overall, we predict a lower average warfarin dose requirement in AI/AN populations in Alaska than that seen in non-AI/AN populations of the USA, a finding consistent with clinical experience in Alaska.

Nutritional and other types of oedema, albumin, complex carbohydrates and the interstitium - a response to Malcolm Coulthard's hypothesis: Oedema in kwashiorkor is caused by hypo-albuminaemia

The various types of oedema in man are considered in relation to Starling's hypothesis of fluid movement from capillaries, with the main emphasis on nutritional oedema and the nephrotic syndrome in children. It is concluded that each condition has sufficient anomalous findings to render Starling's hypothesis untenable. The finding that the endothelial glycocalyx is key to control of fluid movement from and into the capillaries calls for complete revision of our understanding of oedema formation. The factors so far known to affect the function of the glycocalyx are reviewed. As these depend upon sulphated proteoglycans and other glycosaminoglycans, the argument is advanced that the same abnormalities will extend to the interstitial space and that kwashiorkor is fundamentally related to a defect in sulphur metabolism which can explain all the clinical features of the condition, including the formation of oedema.

Congenital analbuminemia caused by a novel aberrant splicing in the albumin gene

Introduction:

Congenital analbuminemia is a rare autosomal recessive disorder manifested by the presence of a very low amount of circulating serum albumin. It is an allelic heterogeneous defect, caused by variety of mutations within the albumin gene in homozygous or compound heterozygous state. Herein we report the clinical and molecular characterization of a new case of congenital analbuminemia diagnosed in a female newborn of consanguineous (first degree cousins) parents from Ankara, Turkey, who presented with a low albumin concentration (< 8 g/L) and severe clinical symptoms.

Materials and methods:

The albumin gene of the index case was screened by single-strand conformation polymorphism, heteroduplex analysis, and direct DNA sequencing. The effect of the splicing mutation was evaluated by examining the cDNA obtained by reverse transcriptase - polymerase chain reaction (RT-PCR) from the albumin mRNA extracted from proband’s leukocytes.

Results:

DNA sequencing revealed that the proband is homozygous, and both parents are heterozygous, for a novel G>A transition at position c.1652+1, the first base of intron 12, which inactivates the strongly conserved GT dinucleotide at the 5′ splice site consensus sequence of this intron. The splicing defect results in the complete skipping of the preceding exon (exon 12) and in a frame-shift within exon 13 with a premature stop codon after the translation of three mutant amino acid residues.

Conclusions:

Our results confirm the clinical diagnosis of congenital analbuminemia in the proband and the inheritance of the trait and contribute to shed light on the molecular genetics of analbuminemia.

Novel therapeutics for the treatment of familial Mediterranean fever: from colchicine to biologics

Familial Mediterranean fever (FMF), an inherited autosomal recessive disorder, is characterized by sporadic, paroxysmal attacks of fever and serosal inflammation, lasting 1-3 days. Patients may develop renal amyloidosis, arthritis, serositis, and skin and oral lesions. Diagnosis is based on clinical features, response to treatment with colchicine, and genetic analysis. Colchicine prevents attacks and renal amyloidosis, in addition to reversing proteinuria. Nonresponders may receive novel therapy, including interleukin (IL)-1 receptor antagonists and IL-1 decoy receptor. Recently, new options have been considered.

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.