A nucleotide insertion and frameshift cause analbuminemia in an Italian family

Congenital Analbuminemia Associated with Hypothyroidism in a Preterm Neonate: The First Case from a Highly Consanguineous Community

Analbuminemia is a rare autosomal recessive disease characterized by extremely low or zero levels of circulating serum albumin. The diagnosis is made by ruling out other causes of hypoalbuminemia and should be confirmed by gene mutation analysis. In this article, we describe the clinical findings of a preterm neonate born to a consanguineous family who presented with progressive lower limb edema at the age of 7 days and who was confirmed as having congenital analbuminemia by genetic testing (homozygous mutation ALB NP_000468.1: p. Val78CysfsTer2) and hypothyroidism. This is the first case of congenital analbuminemia to be reported from Jordan.

Human serum albumin variants in China: a molecular epidemiological investigation and literature review

Background

Bisalbuminemia is a hereditary and/or acquired abnormality characterized by a double albumin (ALB) band on serum protein electrophoresis. However, there have been no epidemiological investigations of ALB variants in Chinese populations.

Methods

This retrospective study examined 71,963 unrelated subjects from five provinces in southern China. ALB variants were screened by cellulose acetate electrophoresis at pH 8.6 and ALB mutations were confirmed by polymerase chain reaction-DNA sequencing.

Results

The average incidence of inherited bisalbuminemia in the southern Chinese population was 0.0264% (19/71,963). Thirteen cases showed slow and six showed fast genetic variants on cellulose acetate electrophoresis. Four kinds of ALB variants were identified: proalbumin Lille (p.Arg23His), ALB Castel di Sangro (p.Lys560Glu), ALB Fukuoka-1 (p.Asp587Asn), and a novel ALB Wuxi (p.Lys562Glu). The gene frequency of ALB variants in the Wuxi region (0.126%, 13/10,297) was significantly higher than in other regions in southern China, and 90.9% (10/11) of cases of proalbumin Lille were also found in the Wuxi region.

Conclusions

This study provides the first report of the detailed prevalence and molecular characterization of ALB variants in southern China. Compared with other areas of China, Wuxi had a different pattern of ALB variants and a high prevalence of proalbumin Lille.

Recurrent Hypoglycemia in a Case of Congenital Analbuminemia

In congenital analbuminemia (CAA), mutations in the albumin gene result in a severe deficiency or absence of plasma albumin. Only about 90 cases have been reported to date, but the specific features of glucose and lipid metabolism in congenital analbuminemia have only been studied in a rat model of analbuminemia. We report the case of a female patient hospitalized for a streptococcal skin infection who showed recurrent hypoglycemia. A diagnosis of CAA was confirmed by mutation analysis and by the detection of a single base variation in the ALB gene. Hypoglycemia was first documented after a fasting period during acute illness. Recurrent hypoglycemia persisted despite good general condition and normal nutrition during antimicrobial therapy with moxifloxacin. Several contributing factors causing this hypoglycemia can be discussed. Individuals with CAA are prone to adverse drug effects caused by changes in drug-protein binding properties. It is unclear if specific changes of glucose and lipid metabolism in CAA constitute a risk factor for hypoglycemia.

Congenital Analbuminemia in a Korean Male Diagnosed with Single Nucleotide Polymorphism in the ALB Gene: The First Case Reported in Korea

Congenital analbuminemia (CAA) is an autosomal recessive disease characterized by extremely low serum levels of albumin. CAA is caused by various homozygous or heterozygous mutations of the ALB gene. Patients often exhibit no clinical symptoms, aside from rare accompanying conditions, such as fatigue, ankle edema, and hypotension. This case report describes the case of a 28-year-old asymptomatic Korean male referred to our center with hypocalcemia, vitamin D deficiency, and hypoalbuminemia who was diagnosed with CAA. To determine the cause of hypoalbuminemia in the patient, laboratory tests, radiological examination, and DNA sequencing were performed. The patient was confirmed to not exhibit any other clinical conditions that can induce hypoalbuminemia and was diagnosed with CAA using DNA sequencing. The present case of CAA is the first to be reported in Korea.

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.

Congenital analbuminemia in a patient affected by hypercholesterolemia: A case report

BACKGROUND

Congenital analbuminemia (CAA) is a very rare disorder. Our data describes the clinical features and laboratory results of a new case established by mutation analysis of the albumin gene in a 39-year-old woman presenting with hypercholesterolemia. Our findings contribute to shed light on the molecular genetics of the disorder and confirm that safe and well tolerated hypocholesterolemic treatment with atorvastatin may be administered in dislipidemic patient with CAA in order to reduce their cardiovascular risk.

CASE SUMMARY

Our patient presented with a history of hypercholesterolemia and referred asthenia and heaviness in both legs. She was born from healthy and non-consanguineous parents and her development was normal. She had not familiarity for early cardiovascular disease, and did not report personal history of hypertension, chronic kidney or liver diseases. Clinical laboratories results showed critically reduced value of albumin whereas other serum proteins were elevated. Main causes of hypoalbuminemia (proteinuria, inflammatory state and insufficient hepatic synthesis) were ruled out by normal procedures and laboratory tests. So the hypothesis of a CAA was tested through mutation analysis of the albumin gene that revealed a homozygous CA deletion in exon 12, at nucleotide positions c1614-1615. This finding brought to the diagnosis of CAA. Currently the patient receives Atorvastatin 20 mg od and undergoes clinical and laboratory follow-up every six months. She never needed albumin infusions.

CONCLUSION

Our experience shows how treatment with atorvastatin may be safely administered and well tolerated in patients affected by CAA.

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.

Human plasma lipocalins and serum albumin: Plasma alternative carriers?

Lipocalins are an evolutionarily conserved family of proteins that bind and transport a variety of exogenous and endogenous ligands. Lipocalins share a conserved eight anti-parallel β-sheet structure. Among the different lipocalins identified in humans, α-1-acid glycoprotein (AGP), apolipoprotein D (apoD), apolipoprotein M (apoM), α1-microglobulin (α1-m) and retinol-binding protein (RBP) are plasma proteins. In particular, AGP is the most important transporter for basic and neutral drugs, apoD, apoM, and RBP mainly bind endogenous molecules such as progesterone, pregnenolone, bilirubin, sphingosine-1-phosphate, and retinol, while α1-m binds the heme. Human serum albumin (HSA) is a monomeric all-α protein that binds endogenous and exogenous molecules like fatty acids, heme, and acidic drugs. Changes in the plasmatic levels of lipocalins and HSA are responsible for the onset of pathological conditions associated with an altered drug transport and delivery. This, however, does not necessary result in potential adverse effects in patients because many drugs can bind both HSA and lipocalins, and therefore mutual compensatory binding mechanisms can be hypothesized. Here, molecular and clinical aspects of ligand transport by plasma lipocalins and HSA are reviewed, with special attention to their role as alterative carriers in health and disease.

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.

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.

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

BACKGROUND

Analbuminemia (OMIM # 103600) is a rare autosomal recessive disorder manifested by the absence or severe reduction of circulating serum albumin in homozygous or compound heterozygous subjects. The trait is caused by a variety of mutations within the albumin gene.

DESIGN

We report here the clinical and molecular characterisation of two new cases of congenital analbuminemia diagnosed in two members of the Druze population living in a Galilean village (Northern Israel) on the basis of their low level of circulating albumin. The albumin gene was screened by single-strand conformation polymorphism and heteroduplex analysis, and the mutated region was submitted to DNA sequencing.

RESULTS

Both the analbuminemic subjects resulted homozygous for a previously unreported c.1 A>C transversion, for which we suggest the name Afula from the hospital where the two cases were investigated. This mutation causes the loss of the primary start codon ATG for Met1, which is replaced by a - then untranslated - triplet CTG for Leu. (p.Met1Leu). The use of an alternative downstream ATG codon would probably give rise to a completely aberrant polypeptide chain, leading to a misrouted intracellular transport and a premature degradation.

CONCLUSIONS

The discovery of this new ALB mutation, probably inherited from a common ancestor, sheds light on the molecular mechanism underlying the analbuminemic trait and may serve in the development of a rapid genetic test for the identification of a-symptomatic heterozygous carriers in the Druze population in the Galilee.

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.

Human serum albumin: from bench to bedside

Human serum albumin (HSA), the most abundant protein in plasma, is a monomeric multi-domain macromolecule, representing the main determinant of plasma oncotic pressure and the main modulator of fluid distribution between body compartments. HSA displays an extraordinary ligand binding capacity, providing a depot and carrier for many endogenous and exogenous compounds. Indeed, HSA represents the main carrier for fatty acids, affects pharmacokinetics of many drugs, provides the metabolic modification of some ligands, renders potential toxins harmless, accounts for most of the anti-oxidant capacity of human plasma, and displays (pseudo-)enzymatic properties. HSA is a valuable biomarker of many diseases, including cancer, rheumatoid arthritis, ischemia, post-menopausal obesity, severe acute graft-versus-host disease, and diseases that need monitoring of the glycemic control. Moreover, HSA is widely used clinically to treat several diseases, including hypovolemia, shock, burns, surgical blood loss, trauma, hemorrhage, cardiopulmonary bypass, acute respiratory distress syndrome, hemodialysis, acute liver failure, chronic liver disease, nutrition support, resuscitation, and hypoalbuminemia. Recently, biotechnological applications of HSA, including implantable biomaterials, surgical adhesives and sealants, biochromatography, ligand trapping, and fusion proteins, have been reported. Here, genetic, biochemical, biomedical, and biotechnological aspects of HSA are reviewed.

Molecular diagnosis of analbuminemia: a new case caused by a nonsense mutation in the albumin gene

Analbuminemia is a rare autosomal recessive disorder manifested by the absence, or severe reduction, of circulating serum albumin (ALB). We report here a new case diagnosed in a 45 years old man of Southwestern Asian origin, living in Switzerland, on the basis of his low ALB concentration (0.9 g/L) in the absence of renal or gastrointestinal protein loss, or liver dysfunction. The clinical diagnosis was confirmed by a mutational analysis of the albumin (ALB) gene, carried out by single-strand conformational polymorphism (SSCP), heteroduplex analysis (HA), and DNA sequencing. This screening of the ALB gene revealed that the proband is homozygous for two mutations: the insertion of a T in a stretch of eight Ts spanning positions c.1289 + 23–c.1289 + 30 of intron 10 and a c.802 G > T transversion in exon 7. Whereas the presence of an additional T in the poly-T tract has no direct deleterious effect, the latter nonsense mutation changes the codon GAA for Glu244 to the stop codon TAA, resulting in a premature termination of the polypeptide chain. The putative protein product would have a length of only 243 amino acid residues instead of the normal 585 found in the mature serum albumin, but no evidence for the presence in serum of such a truncated polypeptide chain could be obtained by two dimensional electrophoresis and western blotting analysis.

A novel frameshift deletion in the albumin gene causes analbuminemia in a young Turkish woman

BACKGROUND

Analbuminemia is a rare autosomal recessive disorder manifested by the absence, or severe reduction, of circulating serum albumin. The analbuminemic trait was diagnosed in a young Turkish woman on the basis of her clinical symptoms (bilateral lower limb edema) and biochemical findings (minimal albumin amount and variable increases in other protein fractions).

METHODS

Total DNA from the analbuminemic proband and her parents was PCR-amplified using oligonucleotide primers designed to amplify the 14 exons of the albumin gene (ALB) and the flanking intron regions. The products were screened for mutations by single-strand conformation polymorphism (SSCP) and heteroduplex analyses (HA).

RESULTS

HA allowed the identification of the mutation site in exon 12. Direct DNA sequencing of this abnormal fragment revealed that the analbuminemic trait was caused by a homozygous CA deletion at nucleotide positions c. 1614-1615 in the codons for Cys538 and Thr539. The subsequent frameshift should give rise to a putative truncated albumin variant in which the sequence Cys(538)-Thr-Leu-Ser has been changed to Cys(538)-Thr-Phe-Stop. The parents were heterozygous for the same mutation.

CONCLUSIONS

Gel-based mutation detection and DNA sequencing substantiate the clinical diagnosis of congenital analbuminemia in our patient and show that the condition is caused by a novel mutation within the ALB gene. These results contribute to shed light on the molecular basis of this rare condition.

A novel frame-shift deletion causing analbuminaemia in an Italian paediatric patient

BACKGROUND

Analbuminaemia (OMIM #103600) is a rare autosomal recessive disorder manifested by the absence or severe reduction of circulating serum albumin in homozygous or compound heterozygous subjects. The trait is caused by a variety of mutations within the albumin gene.

DESIGN

We report here the clinical and molecular characterization of a new case of congenital analbuminaemia in a 4-year-old Italian girl diagnosed on the basis of the low level of circulating albumin (= 10.0 g L(-1)). The albumin gene was screened by single-strand conformation polymorphism and heteroduplex analysis and the mutated region submitted to DNA sequencing.

RESULTS

The proband was found to be homozygous, and both parents heterozygous, for a novel deletion in exon 8 (c.920delT). The subsequent frame-shift should have given rise to a putative polypeptide chain of 304 amino acid residues, which we could not identify in the proband's serum.

CONCLUSIONS

A novel analbuminaemia causing mutation was identified and characterized at the clinical level in a child. The molecular diagnosis of the trait is based on the rapid localization of the mutation within the albumin gene by single-strand conformation polymorphism and heteroduplex analysis, followed by DNA sequencing of the mutated region.

Trans-splicing into highly abundant albumin transcripts for production of therapeutic proteins in vivo

Spliceosome-mediated RNA trans-splicing has emerged as an exciting mode of RNA therapy. Here we describe a novel trans-splicing strategy, which targets highly abundant pre-mRNAs, to produce therapeutic proteins in vivo. First, we used a pre-trans-splicing molecule (PTM) that mediated trans-splicing of human apolipoprotein A-I (hapoA-I) into the highly abundant mouse albumin exon 1. Hydrodynamic tail vein injection of the hapoA-I PTM plasmid in mice followed by analysis of the chimeric transcripts and protein, confirmed accurate and efficient trans-splicing into albumin pre-mRNA and production of hapoA-I protein. The versatility of this approach was demonstrated by producing functional human papillomavirus type-16 E7 (HPV16-E7) single-chain antibody in C57BL/6 mice and functional factor VIII (FVIII) and phenotypic correction in hemophilia A mice. Altogether, these studies demonstrate that trans-splicing to highly abundant albumin transcripts can be used as a general platform to produce therapeutic proteins in vivo.

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.

Analbuminemia Produced by a Novel Splicing Mutation

Analbuminemia is a rare autosomal recessive disorder manifested by the absence or severe reduction of circulating human serum albumin in homozygous or compound heterozygous individuals. It is an allelic heterogeneous defect, caused by a variety of mutations within the albumin gene. The analbuminemic condition was diagnosed in a Turkish female infant on the basis of low albumin concentration (∼9.0 g/L). The albumin gene was screened by single-strand conformation polymorphism and heteroduplex analysis and submitted to direct sequencing. The proband was found to be homozygous for a T→C transition at nucleotide 13381, the 2nd base of intron 11. The effect of this previously unreported mutation, which inactivates the strongly conserved GT dinucleotide at the 5′ splice site consensus sequence of intron 11, was evaluated by examining the cDNA obtained by reverse transcription-PCR from the albumin mRNA extracted from the proband leukocytes. This analysis revealed that the mutation, named Bartin for the geographical origin of the patient’s family, results in the skipping of exon 11. The subsequent frameshift within exon 12 originates a premature stop codon located 5 codons downstream at position 411. The predicted translation product would consist of 410 amino acids. This novel extensive cDNA alteration is responsible for the analbuminemic trait.

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

BACKGROUND

Analbuminemia is a rare autosomal recessive disorder manifested by the absence, or severe reduction, of circulating serum albumin. Here we report three new cases of hereditary analbuminemia, fortuitously detected in three Slovak Romany children, members of the same family, and define the molecular defect that causes the analbuminemic trait.

METHODS

Total DNA, extracted from peripheral blood samples from six members of the family, was PCR-amplified using oligonucleotide primers designed to amplify the 14 exons of the human albumin gene and the flanking intron regions. The products were screened for mutations by single-strand conformation polymorphism (SSCP) and heteroduplex analyses (HA). HA allowed the identification of the abnormal fragment, which was then sequenced.

RESULTS

In the 3 patients the analbuminemic trait was caused by the same mutation, an AT deletion at nucleotides 2430-31, the 91 th and 92 th bases of exon 3. This defect, previously identified as Kayseri mutation, produces a frameshift leading to a premature stop, two codons downstream. The predicted translation product would consist of 54 amino acid residues. The parents were found to be heterozygous for the mutation.

CONCLUSIONS

Our results confirm that the combination of SSCP and HA represents a powerful tool to study the molecular defects causing analbuminemia in humans.

Analbuminemia in a Swiss family is caused by a C → T transition at nucleotide 4446 of the albumin gene

OBJECTIVE

To define the molecular defect that causes analbuminemia in an apparently healthy boy, son of non-consanguineous Swiss parents.

DESIGN AND METHODS

Total DNA, extracted from peripheral blood samples from the proband and from both parents, was PCR-amplified using oligonucleotide primers designed to amplify the 14 exons of the human albumin gene and the flanking intron regions. The products were screened for mutations by single-strand conformation polymorphism (SSCP) and heteroduplex analyses (HA) either directly or after digestion with restriction enzymes. The combination of these methods identified the abnormal fragment, which was then sequenced.

RESULTS

DNA sequence analysis identified in the homozygous proband a C --> T transition at nucleotide 4446. The mutation changes the codon CGA for Arg 114 to a stop codon TGA, resulting in premature termination and is therefore responsible for the analbuminemic trait. The same mutation has been previously reported to cause analbuminemia in an American female. The putative protein product would have a length of 113 residues. The parents were found to be heterozygous for the mutation.

CONCLUSIONS

Gel-based mutation detection and DNA sequencing confirmed the diagnosis of congenital analbuminemia in the proband. Our results show that the combination of SSCP and HA represents a powerful tool to study the molecular defects causing analbuminemia in humans.

Congenital analbuminaemia: biochemical and clinical implications. A case report and literature review

Congenital analbuminaemia was diagnosed in a small-for-gestational-age neonate presenting with placental and body oedema, an unusual presentation of this rare autosomal recessive disorder. A review of 39 reported cases in the literature shows that the clinical symptoms are always remarkably mild and that the diagnosis is rarely made in infancy. The absence of albumin appears to be partly counterbalanced by high levels of non-albumin proteins and circulatory adaptations. However, congenital analbuminemia can have important complications: lipodystrophy and hypercholesterolaemia, possibly leading to atherosclerosis. Other possible complications reported in literature are hypercoagulability, osteoporosis, respiratory tract infections, intrauterine growth retardation and intrauterine death. Moreover, albumin-binding drugs should be used with caution.

CONCLUSION

Congenital analbuminaemia is a rare disorder with remarkably mild signs and symptoms at all ages. Although often thought to be innocent, this disorder may have important clinical complications.

An outline of inherited disorders of the thyroid hormone generating system

To date, various genetic defects impairing the biosynthesis of thyroid hormone have been identified. These congenital heterogeneous disorders result from mutations of genes involved in many steps of thyroid hormone synthesis, storage, secretion, delivery, or utilization. In contrast to thyroid dyshormonogenesis, the elucidation of the underlying etiology of most cases of thyroid dysgenesis is much less understood. It is suggested that genetic factors might play a role in some cases of thyroid dysgenesis and the best candidate genes involved are those encoding transcription factors known to play a role in the embryonic development of the thyroid gland. Moreover, discordance for thyroid dysgenesis is the rule for monozygotic twins as recently reported and this may result from epigenetic phenomena, early somatic mutations, or postzygotic events. In the final part of this review the molecular defects involved in proteins that transport thyroid hormone in the circulation are described: thyroxine-binding globulin (TBG), transtiretin and albumin, that may be associated with altered thyroid function tests and other pathologic conditions such as amyloidotic polyneuropathy.

Idiopathic hypoalbuminemia explained by reduced synthesis rate and an increased catabolic rate

OBJECTIVE

To determine the contribution of albumin synthetic and catabolic rates to steady state levels in a patient with idiopathic hypoalbuminemia.

METHODS

Using L-[1-(13)C] valine, both FSR (fractional synthesis rate) as well as FCR (fractional catabolic rate) were studied. Human albumin cDNA analysis and determination of the exact albumin mass by electrospray mass spectrometry were performed.

RESULTS

Compared with controls, plasma albumin concentration in the patient was reduced (6.7 vs. 37.0 +/- 2.6 g/L). Albumin FSR (= FCR in steady state) was increased compared to controls. The ASR (absolute synthesis rate) of albumin was decreased based on the enrichment in plasma valine and KIV, but estimated to be normal based on VLDL apoB100 at plateau compared to controls. Direct estimation of albumin FCR rejected the latter. No mutation was found in the transcribed region of albumin gene. The exact mass of albumin (66.493 Da) was not different from controls.

CONCLUSION

The hypoalbuminemia was a result of accelerated clearance of albumin from plasma in addition to defective albumin synthesis. This study also shows that the chosen method of the precursor pool could lead to misinterpretation of data in hepatic protein synthesis.

Molecular Diagnosis of Analbuminemia: A Novel Mutation Identified in Two Amerindian and Two Turkish Families

Background: Analbuminemia is a rare autosomal recessive disorder in which individuals have little or no circulating albumin, usually the most abundant plasma protein. We describe a new mutation associated with analbuminemia.

Methods: We studied four apparently unrelated patients who had congenital analbuminemia: two of Amerindian and two of Turkish origin. The 14 exons and the flanking intron sequences of the albumin gene were amplified by PCR and screened for mutations by single-strand conformational polymorphism and heteroduplex analysis. The mutated DNA fragments were sequenced directly.

Results: In all four cases, analbuminemia was caused by the same mutation, an AT deletion at nucleotides 2430–2431, the 91st and 92nd bases of exon 3. This novel defect, named Kayseri, produces a frameshift leading to a premature stop two codons downstream. The predicted translation product would consist of 54 amino acid residues.

Conclusions: The AT deletion at nucleotides 2430–2431 is a novel mutation associated with analbuminemia.

A novel splicing mutation causes an undescribed type of analbuminemia

Analbuminemia is a rare autosomal recessive disorder manifested by the absence or severe reduction of circulating serum albumin in homozygous subjects. In this report we describe a new molecular defect that caused the analbuminemic trait in a newborn of Iraqi origin. When the parents' DNA was analyzed, both subjects were found to be heterozygous for the same mutation found in the infant. All the 14 exon and flanking intron sequences of the albumin gene were amplified via PCR and screened for mutations by SSCP and heteroduplex analysis. A mutation in the DNA region encoding exon 1 and its flanking intron was revealed by the presence of a heteroduplex. The fragment, which was directly DNA sequenced, contains a previously unreported single nucleotide change, consisting in a G to A substitution at nucleotide 118 in the structural gene of the human protein. This mutation, involving the first base of intron 1, destroys the GT dinucleotide consensus sequence found at the 5' end of most intervening sequences and causes the defective pre-mRNA splicing responsible for the analbuminemic trait.

A nucleotide insertion and frameshift cause albumin Kénitra, an extended and O-glycosylated mutant of human serum albumin with two additional disulfide bridges

Albumin Kenitra is a new type of genetic variant of human serum albumin that has been found in two members of a family of Sephardic Jews from Kenitra (Morocco). The slow-migrating variant and the normal protein were isolated by anion-exchange chromatography and, after treatment with CNBr, the digests were analyzed by two-dimensional electrophoresis in a polyacrylamide gel. The CNBr peptides of the variant were purified by reverse-phase high performance liquid chromatography and submitted to sequence analysis. Albumin Kenitra is peculiar because it has an elongated polypeptide chain, 601 residues instead of 585, and its sequence is modified beginning from residue 575. DNA structural studies showed that the variant is caused by a single-base insertion, an adenine at nucleotide position 15 970 in the genomic sequence, which leads to a frameshift with the subsequent translation to the first termination codon of exon 15. Mass spectrometric analyses revealed that the four additional cysteine residues of the variant form two new S-S bridges and showed that albumin Kenitra is partially O-glycosylated by a monosialylated HexHexNAc structure. This oligosaccharide chain has been located to Thr596 by amino-acid sequence analysis of the tryptic fragment 592-597.

Albumin banks peninsula: a new termination variant characterised by electrospray mass spectrometry

Albumin Banks Peninsula is an electrophoretically fast variant that is expressed at only 2% of the total serum albumin. Electrospray ionisation analysis indicated a mass decrease of 755 Da relative to normal albumin and carboxypeptidase A digestion, together with CNBr peptide mapping, indicated a C-terminal truncation. This was confirmed by PCR and DNA sequence analysis which showed the introduction of a new AG acceptor splice site near the 3' end of intron 13. Predictably this results in the replacement of the C-terminal GKKLVAASQAALGL sequence by SLCSG and would be associated with an 861 Da decrease in molecular mass. We surmised that the new Cys was most probably cysteinylated as this albumin species would have a mass decrease of 742 Da and be very close to the measured value of 755 Da. Cysteinylation was confirmed when a mass decrease of 863 Da was measured between the proteins after reduction of their disulfide bonds.

Structural characterization of four genetic variants of human serum albumin associated with alloalbuminemia in Italy

A long-term electrophoretic survey on plasma proteins, which was carried out in several clinical laboratories in Italy, identified 28 different genetic variants of human serum albumin and four cases of analbuminemia. We have previously characterized 16 point mutations, 3 C-terminal mutants, and the genetic defects in two analbuminemic subjects. Here, we report the molecular defects of four alloalbumins that have been characterized by protein structural analysis. Of these, three represent new single-point mutations: albumins Tregasio, Val122-->Glu, Bergamo, Asp314-->Gly, and Maddaloni, Val533-->Met. The fourth, albumin Besana Brianza, has the same Asp494-->Asn mutation that introduces a glycosylation site which has been previously reported in a variant from New Zealand, albumin Casebrook. However, in contrast to albumin Casebrook, albumin Besana Brianza is only partially glycosylated and the oligosaccharide is heterogeneous, consisting of a biantennary complex type N-glycan with either two or one sialic acid residue(s) on the antennae. Both albumin Maddaloni and Besana Brianza represent mutations at hypermutable CpG dinucleotide sites; albumin Maddaloni is a mutant that does not involve a charged amino acid.

Lipoprotein kinetics in patients with analbuminemia. Evidence for the role of serum albumin in controlling lipoprotein metabolism

In vitro data suggested that albumin is a key factor controlling apolipoprotein (apo) synthesis by hepatocytes. Studies in analbuminemic rats have shown an increase in secretion of apoB-containing lipoprotein from the liver. We studied the kinetic aspects of apoB- and apoAI-containing lipoprotein metabolism in two sisters with analbuminemia using a constant 14-hour infusion of leucine labeled with stable isotopes. Compared with control subjects, total cholesterol was higher in the two patients (432 and 461 versus 155 +/- 14 mg/dL), as was apoB (257 and 230 versus 72 +/- 7 mg/dL). Triglycerides were slightly increased (134 and 105 versus 89 +/- 9 mg/dL), whereas apoAI was lower (109 and 105 versus 124 +/- 6 mg/dL). VLDL-apoB production was higher, as was the production of IDL-apoB and LDL-apoB (32.8 and 36.0 versus 24.8 +/- 5.9, 32.1 and 27.2 versus 16.4 +/- 2.3, and 14.1 and 17.6 versus 10.3 +/- 1.2 mg.kg-1.d-1, respectively). The fractional catabolic rate of all the apoB-containing lipoproteins was decreased (0.23 and 0.37 versus 0.48 +/- 0.05, 0.27 and 0.28 versus 0.62 +/- 0.08, and 0.012 and 0.009 versus 0.022 +/- 0.002.h-1, respectively). A similar mechanism could explain the dyslipidemia observed in other conditions associated with low albumin levels, such as nephrotic syndrome.

A genetic variant of albumin (albumin Asola; Tyr140-->Cys) with no free -SH group but with an additional disulfide bridge

A slow migrating variant of human serum albumin, present in lower amount than the normal protein, has been detected by routine clinical electrophoresis at pH 8.6 in two members of a family living in Asola (Lombardia, Italy). Ion-exchange chromatography of serum samples failed to separate the normal protein from the variant. Analysis of the albumin peak by SDS/PAGE revealed that the variant had a lower apparent molecular mass than its normal counterpart. However, the abnormal band was not detectable when the separation was performed under reducing conditions or when both albumins were carboxymethylated. Isoelectric-focusing analysis of CNBr fragments localized the mutation to fragment CNBr 3 (residues 124-298). This fragment was isolated on a preparative scale and subjected to tryptic digestion. Sequence determination of the abnormal tryptic peptide revealed that the variant arises from a Tyr140--> Cys substitution. This result was confirmed by DNA sequence analysis, which showed a single transition of TAT-->TGT at nucleotide position 5074. Despite the presence of an additional cysteine residue, several lines of evidence indicated that albumin Asola has no free -SH group; therefore, we propose the formation of a new S-S bond between Cys140 and Cys34, the only free sulphydryl group present in the normal protein. The relatively low level of the variant in serum and its abnormal mobility on cellulose acetate electrophoresis and SDS/PAGE are probably caused by a gross conformational change of the molecule induced by the new S-S bridge.

Analbuminemia: three cases resulting from different point mutations in the albumin gene

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. Analbuminemia 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, (ii) a C-->T transition at nt 4446 for an American female, and (iii) 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 analbuminemia is extremely rare (frequency < 1 x 10(6)); yet the virtual absence of albumin is tolerable despite its multiple functions.

Genetic variants of human serum albumin in Italy: point mutants and a carboxyl-terminal variant

Of the > 50 different genetic variants of human serum albumin (alloalbumins) that have been characterized by amino acid or DNA sequence analysis, almost half have been identified in Italy through a long-term electrophoretic survey of serum. Previously we have reported structural studies of 11 Italian alloalbumins with point mutations, 2 different carboxyl-terminal variants, and 1 case of analbuminemia in an Italian family. This article describes confirmation by DNA sequencing of mutations previously inferred from protein sequencing of 4 of the above alloalbumins; it also reports the mutations identified by protein and DNA sequence analysis of 4 other Italian alloalbumins not previously recorded: albumin Larino, His3-->Tyr; Tradate-2 (protein sequencing only), Lys225-->Gln; Caserta, Lys276-->Asn; and Bazzano, a carboxyl-terminal variant. The first 3 have point mutations that produce a single amino acid substitution, but a nucleotide deletion causes a frameshift and an altered and truncated carboxyl-terminal sequence in albumin Bazzano. In these 4 instances the expression of the alloalbumin is variable, ranging from 10% to 70% of the total albumiN, in contrast to the usual 50% each for the normal and mutant albumin. The distribution of point mutations in the albumin gene is nonrandom; most of the 47 reported point substitutions involve charged amino acid residues on the surface of the molecule that are not concerned with ligand-binding sites.