Molecular analysis of aldolase B genes in hereditary fructose intolerance

Quality of life of adult patients with hereditary fructose intolerance

BACKGROUND

Although patients with hereditary fructose intolerance (HFI) generally have a good prognosis on a fructose-restricted diet, relatively little is known about their quality of life. The aim of this study was to investigate the quality of life in adult patients with HFI in comparison to patients with dietary-treated, classical phenylketonuria (PKU).

METHODS

Patients with HFI and patients with classical PKU were recruited from the adult metabolic centers in The Netherlands and Belgium and via social media. Patients were asked to fill out the 36-item Short Form Health survey (SF-36) and a modified PKU Quality Of Life (PKU-QoL) questionnaire.

RESULTS

Patients with HFI (n = 19) did not report any restrictions in their health-related quality of life, except for vitality and general mental health, which were scored more unfavorable compared to patients with PKU (n = 19) (p < 0.05, adjusted for level of education and country of origin). The results from the modified PKU-QoL demonstrated a statistically significantly greater impact of the disease in the social domain in HFI. A substantial proportion of both HFI and PKU patients (21%) reported a great to severe emotional impact of their disease. Finally, patients with HFI experienced statistically significantly less food temptations, less guilt if dietary restrictions not followed, and less overall difficulty following dietary restrictions.

CONCLUSIONS

Although patients with HFI showed to have a generally good quality of life, they scored lower on vitality and general mental health, and reported a greater social impact of the disease. These aspects deserve further study and clinical attention.

The Network Basis for the Structural Thermostability and the Functional Thermoactivity of Aldolase B

Thermostability is important for the thermoactivity of proteins including enzymes. However, it is still challenging to pinpoint the specific structural factors for different temperature thresholds to initiate their specific structural and functional perturbations. Here, graph theory was used to investigate how the temperature-dependent noncovalent interactions as identified in the structures of aldolase B and its prevalent A149P mutant could form a systematic fluidic grid-like mesh network with topological grids to regulate the structural thermostability and the functional thermoactivity upon cyclization against decyclization in an extended range of a subunit. The results showed that the biggest grid may determine the melting temperature thresholds for the changes in their secondary and tertiary structures and specific catalytic activities. Further, a highly conserved thermostable grid may serve as an anchor to secure the flexible active site to achieve the specific thermoactivity. Finally, higher grid-based systematic thermal instability may disfavor the thermoactivity. Thus, this computational study may provide critical clues for the structural thermostability and the functional thermoactivity of proteins including enzymes.

De novo 11q13.3q13.4 deletion in a patient with Fanconi renotubular syndrome and intellectual disability: Case report and review of literature

Objective

To explore the genetic etiology of a child with facial dysmorphia, developmental delay, intellectual disability, Fanconi renotubular syndrome, and Chiari malformations.

Materials and methods

Whole exome sequencing (WES), Copy number variation sequencing (CNV-seq), and mitochondrial gene detection (Long-PCR + NGS) were applied to detect possible pathogenic mutations and chromosomal copy number variations (CNVs), together with databases and literature reviews to clarify the pathological significance of the candidate mutations.

Results

The WES revealed a 2.10 Mb interstitial deletion from 11q13.3 to 11q13.4, which was later confirmed by CNV-seq involving 11 OMIM genes, among which SHANK2, DHCR7, NADSYN1, FADD, NUMA1, IL18BP, ANO1, and FGF3 are disease-causing. The mitochondrial gene shows no variations.

Conclusion

The child has carried a de novo 11q13.3q13.4 microdeletion, in which SHANK2 genes may be the key gene responsible for the phenotype of intellectual disability. The renal manifestation of the child, which can be diagnosed as Fanconi renotubular syndrome, has an unknown cause but may result from the effect of the ANO1 gene. This case adds a new phenotype to the deletion of this region.

Hereditary fructose intolerance: A comprehensive review

Hereditary fructose intolerance (HFI) is a rare autosomal recessive inherited disorder that occurs due to the mutation of enzyme aldolase B located on chromosome 9q22.3. A fructose load leads to the rapid accumulation of fructose 1-phosphate and manifests with its downstream effects. Most commonly children are affected with gastrointestinal symptoms, feeding issues, aversion to sweets and hypoglycemia. Liver manifestations include an asymptomatic increase of transaminases, steatohepatitis and rarely liver failure. Renal involvement usually occurs in the form of proximal renal tubular acidosis and may lead to chronic renal insufficiency. For confirmation, a genetic test is favored over the measurement of aldolase B activity in the liver biopsy specimen. The crux of HFI management lies in the absolute avoidance of foods containing fructose, sucrose, and sorbitol (FSS). There are many dilemmas regarding tolerance, dietary restriction and occurrence of steatohepatitis. Patients with HFI who adhere strictly to FSS free diet have an excellent prognosis with a normal lifespan. This review attempts to increase awareness and provide a comprehensive review of this rare but treatable disorder.

Epidemiological aspects of hereditary fructose intolerance: A database study

Hereditary fructose intolerance (HFI) is an inborn error of fructose metabolism of autosomal recessive inheritance caused by pathogenic variants in the ALDOB gene that lead to aldolase B deficiency in the liver, kidneys, and intestine. Patients manifest symptoms, such as ketotic hypoglycemia, vomiting, nausea, in addition to hepatomegaly and other liver and kidney dysfunctions. The treatment consists of a fructose-restricted diet, which results in a good prognosis. To analyze the distribution of ALDOB variants described in patients and to estimate the prevalence of HFI based on carrier frequency in the gnomAD database, a systematic review was conducted to assess ALDOB gene variants among patients with HFI. The prevalence of HFI was estimated from the carrier frequency of variants described in patients, as well as rare variants predicted as pathogenic by in silico tools. The p.(Ala150Pro) and p.(Ala175Asp) variants are the most frequent and are distributed worldwide. However, these variants have particular distribution patterns in Europe. The analysis of the prevalence of HFI showed that the inclusion of rare alleles predicted as pathogenic is a more informative approach for populations with few patients. The data show that HFI has a wide distribution and an estimated prevalence of ~1:10,000.

Molecular and clinical findings of Turkish patients with hereditary fructose intolerance

OBJECTIVES

Hereditary fructose intolerance (HFI) is an autosomal recessive disorder caused by a deficiency in aldolase B that can result in hypoglycemia, nausea, vomiting, abdominal pain, liver and kidney dysfunction, coma, and even death. This study aims to represent the clinical features and molecular genetic analysis data of the patients diagnosed with HFI in our study population.

METHODS

The medical records of the 26 patients with HFI were evaluated retrospectively. Age, gender, clinical findings, metabolic crises, and the results of molecular analyses were recorded.

RESULTS

The patients with HFI had a good prognosis and the aversion to sugar-containing foods was the main complaint. Seven different variants were identified in the Aldolase B (ALDOB) gene in HFI patients. The most frequent mutations were p.Ala150Pro, p.Ala175Asp had a prevalence of 61 and 30%, respectively, in agreement with the literature and other known variants were found with minor frequencies c.360-363del4(3.8%), p.Asn335Lys(3.8%), and three novel mutations c.113-1_15del4 (3.8%), p.Ala338Val(7.6%), and p.Asp156His(3.8%) were identified at a heterozygous, homozygous, or compound heterozygous level.

CONCLUSIONS

This study results revealed three novel mutations in patients with HFI. On the basis of age of presentation, clinical symptoms, and metabolic crisis, there was no clear-cut genotype-phenotype correlation. This article also demonstrates the importance of screening suspected infants in cases of acute liver failure for prompt diagnosis and treatment of HFI.

Fructose and Mannose in Inborn Errors of Metabolism and Cancer

History suggests that tasteful properties of sugar have been domesticated as far back as 8000 BCE. With origins in New Guinea, the cultivation of sugar quickly spread over centuries of conquest and trade. The product, which quickly integrated into common foods and onto kitchen tables, is sucrose, which is made up of glucose and fructose dimers. While sugar is commonly associated with flavor, there is a myriad of biochemical properties that explain how sugars as biological molecules function in physiological contexts. Substantial research and reviews have been done on the role of glucose in disease. This review aims to describe the role of its isomers, fructose and mannose, in the context of inborn errors of metabolism and other metabolic diseases, such as cancer. While structurally similar, fructose and mannose give rise to very differing biochemical properties and understanding these differences will guide the development of more effective therapies for metabolic disease. We will discuss pathophysiology linked to perturbations in fructose and mannose metabolism, diagnostic tools, and treatment options of the diseases.

Hereditary Fructose Intolerance Diagnosed in Adulthood

Hereditary fructose intolerance (HFI) is an autosomal recessive disorder caused by a mutation in the aldolase B gene. HFI patients exhibit nausea, vomiting, abdominal pain, hypoglycemia, and elevated liver enzymes after dietary fructose exposure. Chronic exposure might lead to failure to thrive, liver failure, renal failure, and, eventually, death. HFI usually manifests in infants when they are being weaned off of breastmilk. Because HFI has an excellent prognosis when patients maintain a strict restrictive diet, some patients remain undiagnosed due to the voluntary avoidance of sweet foods. In the past, HFI was diagnosed using a fructose tolerance test, liver enzyme assays or intestinal biopsy specimens. Currently, HFI is diagnosed through the analysis of aldolase B mutations. Here, HFI was diagnosed in a 41-year-old woman who complained of sweating, nausea, and vomiting after consuming sweets. She had a compound heterozygous mutation in the aldolase B gene; gene analysis revealed pathogenic nonsense (c.178C>T, p.Arg60Ter) and frameshift (c.360_363delCAAA, p.Asn120LysfsTer32) variants. This is the first report of a Korean HFI patient diagnosed in adulthood.

Novel Fanconi renotubular syndromes provide insights in proximal tubule pathophysiology

The various forms of Fanconi renotubular syndromes (FRTS) offer significant challenges for clinicians and present unique opportunities for scientists who study proximal tubule physiology. This review will describe the clinical characteristics, genetic underpinnings, and underlying pathophysiology of the major forms of FRST. Although the classic forms of FRTS will be presented (e.g., Dent disease or Lowe syndrome), particular attention will be paid to five of the most recently discovered FRTS subtypes caused by mutations in the genes encoding for L-arginine:glycine amidinotransferase (GATM), solute carrier family 34 (type Ii sodium/phosphate cotransporter), member 1 (SLC34A1), enoyl-CoAhydratase/3-hydroxyacyl CoA dehydrogenase (EHHADH), hepatocyte nuclear factor 4A (HNF4A), or NADH dehydrogenase complex I, assembly factor 6 (NDUFAF6). We will explore how mutations in these genes revealed unexpected mechanisms that led to compromised proximal tubule functions. We will also describe the inherent challenges associated with gene discovery studies based on findings derived from small, single-family studies by focusing the story of FRTS type 2 (SLC34A1). Finally, we will explain how extensive alternative splicing of HNF4A has resulted in confusion with mutation nomenclature for FRTS type 4.

The small intestine shields the liver from fructose-induced steatosis

Per capita fructose consumption has increased 100-fold over the last century¹. Epidemiological studies suggest that excessive fructose consumption, and especially consumption of sweet drinks, is associated with hyperlipidaemia, non-alcoholic fatty liver disease, obesity and diabetes^2-7. Fructose metabolism begins with its phosphorylation by the enzyme ketohexokinase (KHK), which exists in two alternatively spliced forms⁸. The more active isozyme, KHK-C, is expressed most strongly in the liver, but also substantially in the small intestine^9,10 where it drives dietary fructose absorption and conversion into other metabolites before fructose reaches the liver^11-13. It is unclear whether intestinal fructose metabolism prevents or contributes to fructose-induced lipogenesis and liver pathology. Here we show that intestinal fructose catabolism mitigates fructose-induced hepatic lipogenesis. In mice, intestine-specific KHK-C deletion increases dietary fructose transit to the liver and gut microbiota and sensitizes mice to fructose's hyperlipidaemic effects and hepatic steatosis. In contrast, intestine-specific KHK-C overexpression promotes intestinal fructose clearance and decreases fructose-induced lipogenesis. Thus, intestinal fructose clearance capacity controls the rate at which fructose can be safely ingested. Consistent with this, we show that the same amount of fructose is more strongly lipogenic when drunk than eaten, or when administered as a single gavage, as opposed to multiple doses spread over 45 min. Collectively, these data demonstrate that fructose induces lipogenesis when its dietary intake rate exceeds the intestinal clearance capacity. In the modern context of ready food availability, the resulting fructose spillover drives metabolic syndrome. Slower fructose intake, tailored to intestinal capacity, can mitigate these consequences.

Kidney and vascular function in adult patients with hereditary fructose intolerance

Objective: Previous studies have shown that patients with hereditary fructose intolerance (HFI) are characterized by a greater intrahepatic triglyceride content, despite a fructose-restricted diet. The present study aimed to examine the long-term consequences of HFI on other aldolase-B-expressing organs, i.e. the kidney and vascular endothelium.

Methods: Fifteen adult HFI patients were compared to healthy control individuals matched for age, sex and body mass index. Aortic stiffness was assessed by carotid-femoral pulse wave velocity (cf-PWV) and endothelial function by peripheral arterial tonometry, skin laser doppler flowmetry and the endothelial function biomarkers soluble E-selectin [sE-selectin] and von Willebrand factor. Serum creatinine and cystatin C were measured to estimate the glomerular filtration rate (eGFR). Urinary glucose and amino acid excretion and the ratio of tubular maximum reabsorption of phosphate to GFR (TmP/GFR) were determined as measures of proximal tubular function. Results: Median systolic blood pressure was significantly higher in HFI patients (127 versus 122 mmHg, p = .045). Pulse pressure and cf-PWV did not differ between the groups (p = .37 and p = .49, respectively). Of all endothelial function markers, only sE-selectin was significantly higher in HFI patients (p = .004). eGFR was significantly higher in HFI patients than healthy controls (119 versus 104 ml/min/1.73m², p = .001, respectively). All measurements of proximal tubular function did not differ significantly between the groups.

Conclusions: Adult HFI patients treated with a fructose-restricted diet are characterized by a higher sE-selectin level and slightly higher systolic blood pressure, which in time could contribute to a greater cardiovascular risk. The exact cause and, hence, clinical consequences of the higher eGFR in HFI patients, deserves further study.

Recent advances in the pathogenesis of hereditary fructose intolerance: implications for its treatment and the understanding of fructose-induced non-alcoholic fatty liver disease

Hereditary fructose intolerance (HFI) is a rare inborn disease characterized by a deficiency in aldolase B, which catalyzes the cleavage of fructose 1,6-bisphosphate and fructose 1-phosphate (Fru 1P) to triose molecules. In patients with HFI, ingestion of fructose results in accumulation of Fru 1P and depletion of ATP, which are believed to cause symptoms, such as nausea, vomiting, hypoglycemia, and liver and kidney failure. These sequelae can be prevented by a fructose-restricted diet. Recent studies in aldolase B-deficient mice and HFI patients have provided more insight into the pathogenesis of HFI, in particular the liver phenotype. Both aldolase B-deficient mice (fed a very low fructose diet) and HFI patients (treated with a fructose-restricted diet) displayed greater intrahepatic fat content when compared to controls. The liver phenotype in aldolase B-deficient mice was prevented by reduction in intrahepatic Fru 1P concentrations by crossing these mice with mice deficient for ketohexokinase, the enzyme that catalyzes the synthesis of Fru 1P. These new findings not only provide a potential novel treatment for HFI, but lend insight into the pathogenesis of fructose-induced non-alcoholic fatty liver disease (NAFLD), which has raised to epidemic proportions in Western society. This narrative review summarizes the most recent advances in the pathogenesis of HFI and discusses the implications for the understanding and treatment of fructose-induced NAFLD.

Fructosuria and recurrent hypoglycemia in a patient with a novel c.1693T>A variant in the 3' untranslated region of the aldolase B gene

Hereditary fructose intolerance, caused by mutations in the ALDOB gene, is an unusual cause of hypoglycemia. ALDOB encodes the enzyme aldolase B, responsible for the hydrolysis of fructose 1-phosphate in the liver. Here, we report the case of a 33-year-old female patient who consulted due to repetitive episodes of weakness, dizziness and headache after food ingestion. An ambulatory 72-h continuous glucose monitoring revealed multiple short hypoglycemic episodes over the day. After biochemical exclusion of other endocrine causes of hypoglycemia, hereditary fructose intolerance seemed a plausible diagnosis. Repeated measurements of urinary fructose revealed pathologic fructosuria, but genetic testing for the three most common mutations in ALDOB resulted negative. We decided to perform complete Sanger sequencing of the ALDOB gene and encountered a variant consisting of a T>A substitution in position 1963 of the ALDOB transcript (c.1693T>A). This position is located within the 3′ untranslated region of exon 9, 515 nucleotides downstream the stop codon. After complete withdrawal of dietary fructose and sucrose, the patient presented no new hypoglycemic episodes.

Persistent Hypoglycemia in Children: Targeted Gene Panel Improves the Diagnosis of Hypoglycemia Due to Inborn Errors of Metabolism

OBJECTIVES

To evaluate the role of next generation sequencing in genetic diagnosis of pediatric patients with persistent hypoglycemia.

STUDY DESIGN

Sixty-four patients investigated through an extensive workup were divided in 3 diagnostic classes based on the likelihood of a genetic diagnosis: (1) single candidate gene (9/64); (2) multiple candidate genes (43/64); and (3) no candidate gene (12/64). Subsequently, patients were tested through a custom gene panel of 65 targeted genes, which included 5 disease categories: (1) hyperinsulinemic hypoglycemia, (2) fatty acid-oxidation defects and ketogenesis defects, (3) ketolysis defects, (4) glycogen storage diseases and other disorders of carbohydrate metabolism, and (5) mitochondrial disorders. Molecular data were compared with clinical and biochemical data.

RESULTS

A proven diagnosis was obtained in 78% of patients with suspicion for a single candidate gene, in 49% with multiple candidate genes, and in 33% with no candidate gene. The diagnostic yield was 48% for hyperinsulinemic hypoglycemia, 66% per fatty acid-oxidation and ketogenesis defects, 59% for glycogen storage diseases and other carbohydrate disorders, and 67% for mitochondrial disorders.

CONCLUSIONS

This approach provided a diagnosis in ~50% of patients in whom clinical and laboratory evaluation did not allow identification of a single candidate gene and a diagnosis was established in 33% of patients belonging to the no candidate gene class. Next generation sequencing technique is cost-effective compared with Sanger sequencing of multiple genes and represents a powerful tool for the diagnosis of inborn errors of metabolism presenting with persistent hypoglycemia.

Targeting Hepatic Protein Carbonylation and Oxidative Stress Occurring on Diet-Induced Metabolic Diseases through the Supplementation with Fish Oils

The present study addressed the ability of long-chain ω-3 polyunsaturated fatty acids (ω-3 PUFA), i.e., eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), to ameliorate liver protein damage derived from oxidative stress and induced by consumption of high-caloric diets, typical of Westernized countries. The experimental design included an animal model of Sprague-Dawley rats fed high-fat high-sucrose (HFHS) diet supplemented with ω-3 EPA and DHA for a complete hepatic proteome analysis to map carbonylated proteins involved in specific metabolic pathways. Results showed that the intake of marine ω-3 PUFA through diet significantly decreased liver protein carbonylation caused by long-term HFHS consumption and increased antioxidant system. Fish oil modulated the carbonylation level of more than twenty liver proteins involved in critical metabolic pathways, including lipid metabolism (e.g., albumin), carbohydrate metabolism (e.g., pyruvate carboxylase), detoxification process (e.g., aldehyde dehydrogenase 2), urea cycle (e.g., carbamoyl-phosphate synthase), cytoskeleton dynamics (e.g., actin), or response to oxidative stress (e.g., catalase) among others, which might be under the control of diet marine ω-3 PUFA. In parallel, fish oil significantly changed the liver fatty acid profile given by the HFHS diet, resulting in a more anti-inflammatory phenotype. In conclusion, the present study highlights the significance of marine ω-3 PUFA intake for the health of rats fed a Westernized diet by describing several key metabolic pathways which are protected in liver.

Inborn Errors of Metabolism with Hepatopathy: Metabolism Defects of Galactose, Fructose, and Tyrosine

The liver is one of the most essential organs in metabolism and is responsible for metabolizing a wide variety of molecules from amino acids to sugars. Although it is responsible for many essential metabolic processes, it is one of the most severely affected by metabolic disease because, in many cases, it is the first to be exposed to the toxic intermediates. The metabolism of galactose, fructose, and tyrosine involve the liver and although there are systemic findings in metabolic disease involved with these substrates, severe hepatopathy is a common presenting aspect of galactosemia, hereditary fructose intolerance, and tyrosinemia type I.

Management of adults with paediatric-onset chronic liver disease: strategic issues for transition care

Advances in the management of children with chronic liver disease have enabled many to survive into adulthood with or without their native livers, so that the most common of these conditions are becoming increasingly common in adult hepatology practice. Because the aetiologies of chronic liver disease in children may vary significantly from those in adulthood, adults with paediatric-onset chronic liver disease may often present with clinical manifestations unfamiliar to their adulthood physician. Transition of medical care to adult practice requires that the adulthood medical staff (primary physicians and subspecialists) have a comprehensive knowledge of childhood liver disease and their implications, and of the differences in caring for these patients. Pending still unavailable Scientific Society guidelines, this article examines causes, presentation modes, evaluation, management, and complications of the main paediatric-onset chronic liver diseases, and discusses key issues to aid in planning a program of transition from paediatric to adult patients.

Bifunctional homodimeric triokinase/FMN cyclase: contribution of protein domains to the activities of the human enzyme and molecular dynamics simulation of domain movements

Mammalian triokinase, which phosphorylates exogenous dihydroxyacetone and fructose-derived glyceraldehyde, is neither molecularly identified nor firmly associated to an encoding gene. Human FMN cyclase, which splits FAD and other ribonucleoside diphosphate-X compounds to ribonucleoside monophosphate and cyclic X-phosphodiester, is identical to a DAK-encoded dihydroxyacetone kinase. This bifunctional protein was identified as triokinase. It was modeled as a homodimer of two-domain (K and L) subunits. Active centers lie between K1 and L2 or K2 and L1: dihydroxyacetone binds K and ATP binds L in different subunits too distant (≈ 14 Å) for phosphoryl transfer. FAD docked to the ATP site with ribityl 4'-OH in a possible near-attack conformation for cyclase activity. Reciprocal inhibition between kinase and cyclase reactants confirmed substrate site locations. The differential roles of protein domains were supported by their individual expression: K was inactive, and L displayed cyclase but not kinase activity. The importance of domain mobility for the kinase activity of dimeric triokinase was highlighted by molecular dynamics simulations: ATP approached dihydroxyacetone at distances below 5 Å in near-attack conformation. Based upon structure, docking, and molecular dynamics simulations, relevant residues were mutated to alanine, and kcat and Km were assayed whenever kinase and/or cyclase activity was conserved. The results supported the roles of Thr(112) (hydrogen bonding of ATP adenine to K in the closed active center), His(221) (covalent anchoring of dihydroxyacetone to K), Asp(401) and Asp(403) (metal coordination to L), and Asp(556) (hydrogen bonding of ATP or FAD ribose to L domain). Interestingly, the His(221) point mutant acted specifically as a cyclase without kinase activity.

Integration of PCR-Sequencing Analysis with Multiplex Ligation-Dependent Probe Amplification for Diagnosis of Hereditary Fructose Intolerance

Mutations in the ALDOB gene impair the activity of the hepatic aldolase B enzyme, causing hereditary fructose intolerance (HFI), an inherited autosomic recessive disease of carbohydrate metabolism, that can result in hypoglycemia, liver and kidney failure, coma, and death. Noninvasive diagnosis is possible by identifying mutant ALDOB alleles in suspected patients. We report the genetic characterization of a cohort of 18 HFI Caucasian patients, based on PCR-sequencing and Multiplex Ligation-dependent Probe Amplification (MLPA), with the identification of two novel genetic lesions: a small duplication c.940_941dupT (p.Trp314fsX22) and a large deletion encompassing the promoter region and exon 1. MLPA and long range-PCR (LR-PCR) also identified the recently reported g.7840_14288del6448 allele with a surprisingly high frequency (11%) within our patients' cohort. The most common p.Ala150Pro (44%), p.Ala175Asp (19%), p.Asn335Lys (8%), and/or the known c.360-363del4 (5%), p.Tyr204X (2.8%), IVS6 -2A>G (2.8%) mutant alleles were identified in 14 patients at a homozygous or compound-heterozygous level. The integration of PCR-sequencing analysis with exon-dosage tools [MLPA and quantitative fluorescent multiplex-PCR (QFM-PCR)] led to the full genotyping of patients within our cohort and to the identification of the new deletion encompassing the promoter region and exon 1.

A Novel Frameshift Mutation of the ALDOB Gene in a Korean Girl Presenting with Recurrent Hepatitis Diagnosed as Hereditary Fructose Intolerance

Hereditary fructose intolerance is an autosomal recessive disorder that is caused by a deficiency in fructose-1-phosphate aldolase (Aldolase B). Children can present with hypoglycemia, jaundice, elevated liver enzymes and hepatomegaly after intake of dietary fructose. Long-term intake of fructose in undiagnosed patients can result in hepatic failure or renal failure. We experienced a case of hereditary fructose intolerance presenting as recurrent hepatitis-like episodes. Detailed evaluation of her dietary habits revealed her avoidance of sweetened foods and fruits. Genetic analysis of ALDOB revealed that she is a homozygote for a novel frameshifting mutation c[758_759insT]+[758_759insT] (p.[val25 3fsX24]+[val253fsX24]). This report is the first of a Korean patient diagnosed with hereditary fructose intolerance using only molecular testing without undergoing intravenous fructose tolerance test or enzyme assay.

Biopsy Diagnosis of Inherited Liver Disease

Hepatic dysfunction during childhood can be due to acquired or inherited etiologies or a combination. The distinction can be difficult to make on liver biopsy, because the inherited disorders are rare and often lack pathognomonic light microscopic features. Recent progress in understanding the pathogenesis of these disorders has led to advances in molecular genetic screening and confirmatory tests. For a majority of these disorders, the liver biopsy continues to play a crucial role in primary diagnosis or confirmation. This article discusses algorithms that may aid pathologists in differential diagnosis of common inherited disorders of the liver, with emphasis on ancillary diagnostic tools and reference assays that are critical in establishing the diagnosis.

The biochemical basis of hereditary fructose intolerance

Hereditary fructose intolerance is a rare, but potentially lethal, inherited disorder of fructose metabolism, caused by mutation of the aldolase B gene. Treatment currently relies solely on dietary restriction of problematic sugars. Biochemical study of defective aldolase B enzymes is key to revealing the molecular basis of the disease and providing a stronger basis for improved treatment and diagnosis. Such studies have revealed changes in enzyme activity, stability and oligomerisation. However, linking these changes to disease phenotypes has not always been straightforward. This review gives a general overview of the features of hereditary fructose intolerance, then concentrates on the biochemistry of the AP variant (Ala149Pro variant of aldolase B) and molecular pathological consequences of mutation of the aldolase B gene.

Increased prevalence of mutant null alleles that cause hereditary fructose intolerance in the American population

Mutations in the aldolase B gene (ALDOB) impairing enzyme activity toward fructose-1-phosphate cleavage cause hereditary fructose intolerance (HFI). Diagnosis of the disease is possible by identifying known mutant ALDOB alleles in suspected patients; however, the frequencies of mutant alleles can differ by population. Here, 153 American HFI patients with 268 independent alleles were analyzed to identify the prevalence of seven known HFI-causing alleles (A149P, A174D, N334K, Delta4E4, R59Op, A337V, and L256P) in this population. Allele-specific oligonucleotide hybridization analysis was performed on polymerase chain reaction (PCR)-amplified genomic DNA from these patients. In the American population, the missense mutations A149P and A174D are the two most common alleles, with frequencies of 44% and 9%, respectively. In addition, the nonsense mutations Delta4E4 and R59Op are the next most common alleles, with each having a frequency of 4%. Together, the frequencies of all seven alleles make up 65% of HFI-causing alleles in this population. Worldwide, these same alleles make up 82% of HFI-causing mutations. This difference indicates that screening for common HFI alleles is more difficult in the American population. Nevertheless, a genetic screen for diagnosing HFI in America can be improved by including all seven alleles studied here. Lastly, identification of HFI patients presenting with classic symptoms and who have homozygous null genotypes indicates that aldolase B is not required for proper development or metabolic maintenance.

Hereditary fructose intolerance: frequency and spectrum mutations of the aldolase B gene in a large patients cohort from France--identification of eight new mutations

We investigated the molecular basis of hereditary fructose intolerance (HFI) in 160 patients from 92 families by means of a PCR-based mutation screening strategy, consisting of restriction enzyme digestion and direct sequencing. Sixteen different mutations of the aldolase B (ALDOB) gene were identified in HFI patients. As in previous studies, p.A150P (64%), p.A175D (16%) and p.N335K (5%) were the most common mutated alleles, followed by p.R60X, p.A338V, c.360_363delCAAA (p.N120KfsX30), c.324G>A (p.K108K) and c.625-1G>A. Eight novel mutations were also identified in 10 families with HFI: a one-base deletion (c.146delT (p.V49GfsX27)), a small deletion (c.953del42bp), a small insertion (c.689ins TGCTAA (p.K230MfsX136)), one splice site mutation (c.112+1G>A), one nonsense mutation (c.444G>A (p.W148X)), and three missense mutations (c.170G>C (p.R57P), c.839C>A (p.A280P) and c.932T>C (p.L311P)). Our strategy allows to diagnose 75% of HFI patients using restriction enzymatic analysis and to enlarge the diagnosis to 97% of HFI patients when associated with direct sequencing.

Different genotypes in a large Italian family with recurrent hereditary fructose intolerance

OBJECTIVES

Hereditary fructose intolerance is caused by a deficiency of the aldolase B enzyme, which is expressed in the liver, small intestine and kidneys. Patients usually show a marked aversion to fruits and sweets; if, however, it is not diagnosed, persistent or incidental ingestion of fructose might be lethal. Our paper aims at improving the clinical and molecular characterizations of these patients, to avoid dangerous misdiagnoses.

METHODS

Here we report the molecular results in an Italian cohort: on the occurrence of aldolase B mutations and, in particular, on the clinical and molecular characterization of a large family with recurrent hereditary fructose intolerance.

RESULTS

Patients included in our cohort showed the three most common mutations (p.A150P, p.A175D and p.N335K). Such molecular tests were enough to cover all the mutated alleles of hereditary fructose intolerance found in our patients. The allele frequencies of hereditary fructose intolerance mutations detected were 69.2% for p.A150P, 23.1% for p.A175D and 7.7% for p.N335K. The proband of the family with recurrence of the disease was heterozygous for the known p.A150P and p.A175D mutated alleles of the aldolase B gene. Molecular characterization of at-risk family members also identified the p.N335K mutation. In addition, the oldest affected patients exhibited mild clinical impairment.

CONCLUSIONS

Our results indicate that the diagnosis of hereditary fructose intolerance can be complicated by clinical and genetic intrafamilial variability. A knowledge of the clinical and geographical history of each family member is thus essential, to reduce potentially lethal misdiagnoses and to facilitate such patients to receive appropriate genetic counselling.

Semi-automated, reverse-hybridization detection of multiple mutations causing hereditary fructose intolerance

Hereditary fructose intolerance (HFI) is a potentially fatal nutritional disease that is caused by mutations in the liver isoenzyme of fructoaldolase (aldolase B). Our aim was to evaluate a diagnostic assay capable of simultaneously analyzing three-point mutations and a small deletion in the aldolase B (ALDOB) gene. The test under investigation is based on multiplex DNA amplification and hybridization to membrane strips presenting a parallel array of allele-specific oligonucleotide probes. We used the novel reverse-hybridization (RH) protocol to analyze 54 individuals previously genotyped by direct sequencing. RH genotyping for ALDOB mutations Delta4E4, A149P, A174D, and N334K was in complete concordance with results obtained by DNA sequencing. The procedure is rapid (<6h) and may be automated to a large extent. The RH assay tested in this study represents an accurate and robust screening tool to identify common ALDOB mutations.

Aldolase B mutations and prevalence of hereditary fructose intolerance in a Polish population

We studied 28 Polish hereditary fructose intolerant (HFI) patients (26 unrelated) by direct sequencing of the ALDOB coding region/splice sites. Eight different mutations were found including two novel ones (each found in two unrelated individuals): c.250delC (frameshift) and c.522 C > G (p.Y174X). The most frequent mutation c.448 G > C (p.A150P, 67% of chromosomes) was screened for in a group of 1049 randomly selected unrelated individuals. Eight (1:131) carriers were found allowing to estimate the HFI prevalence in Poland as 1:31,000.

Simple method for detection of mutations causing hereditary fructose intolerance

Aldolase B is critical for sugar metabolism, and a catalytic deficiency due to mutations in its gene may result in hereditary fructose intolerance (HFI) syndrome, with hypoglycaemia and severe abdominal symptoms. This report describes two cases of HFI, which were identified by intravenous fructose tolerance test and a new RFLP (restriction fragment length polymorphism) test that detects the two most common mutations, A149P and A174D. The method includes PCR of a 224-base-pair segment of exon 5, a subsequent 3 h incubation with Cac8I and agarose electrophoresis, which reveals either or both of the mutations in one single reaction. The method might be useful for screening of these mutations, which may account for more than 70% of the mutations causing HFI.

The genetic consequences of our sweet tooth

First reported in 1956, hereditary fructose intolerance (HFI) illustrates vividly how interactions between genes and nutrients can influence taste preferences; the disease also reflects the ascendancy of sucrose and fructose as energy sources and as the world's principal sweeteners. However, HFI is not the only genetic ill to have emerged from our obsession with sugar: the slave trade, which had such a key part in the development of the sugar industry, also included major genetic consequences in its haunting legacy.

Mutation analysis in Turkish patients with hereditary fructose intolerance

Thirteen Turkish patients with hereditary fructose intolerance (HFI) were screened for the three common mutations, A149P, A174D and N334K, in the aldolase B gene that have been detected frequently in European population. We found that nine of the patients carry the A149P mutation in both alleles, which corresponds to a frequency of about 55%. Single-strand conformation analysis of all coding exons of the gene was also performed to detect unknown mutations in four patients not carrying the three common mutations. No aberrant migration patterns were observed in these patients.

A system for specific, high-throughput genotyping by allele-specific primer extension on microarrays

This study describes a practical system that allows high-throughput genotyping of single nucleotide polymorphisms (SNPs) and detection of mutations by allele-specific extension on primer arrays. The method relies on the sequence-specific extension of two immobilized allele-specific primers that differ at their 3'-nucleotide defining the alleles, by a reverse transcriptase (RT) enzyme at optimized reaction conditions. We show the potential of this simple one-step procedure performed on spotted primer arrays of low redundancy by generating over 8000 genotypes for 40 mutations or SNPs. The genotypes formed three easily identifiable clusters and all known genotypes were assigned correctly. Higher degrees of multiplexing will be possible with this system as the power of discrimination between genotypes remained unaltered in the presence of over 100 amplicons in a single reaction. The enzyme-assisted reaction provides highly specific allele distinction, evidenced by its ability to detect minority sequence variants present in 5% of a sample at multiple sites. The assay format based on miniaturized reaction chambers at standard 384-well spacing on microscope slides carrying arrays with two primers per SNP for 80 samples results in low consumption of reagents and makes parallel analysis of a large number of samples convenient. In the assay one or two fluorescent nucleotide analogs are used as labels, and thus the genotyping results can be interpreted with presently available array scanners and software. The general accessibility, simple set-up, and the robust procedure of the array-based genotyping system described here will offer an easy way to increase the throughput of SNP typing in any molecular biology laboratory.

Hereditary fructose intolerance and alpha(1) antitrypsin deficiency

A patient with coexisting hereditary fructose intolerance (HFI) and alpha(1) antitrypsin deficiency (alpha(1)ATD) is described. Protease inhibitor typing was not conclusive, presumably because of impaired N-glycosylation secondary to HFI. The case underlines the diagnostic role of molecular genetic techniques in inborn errors of metabolism.

Expression, purification, and characterization of natural mutants of human aldolase B. Role of quaternary structure in catalysis

Fructaldolases (EC 4.1.2.13) are ancient enzymes of glycolysis that catalyze the reversible cleavage of phosphofructose esters into cognate triose (phosphates). Three vertebrate isozymes of Class I aldolase have arisen by gene duplication and display distinct activity profiles with fructose 1,6-bisphosphate and with fructose 1-phosphate. We describe the biochemical and biophysical characterization of seven natural human aldolase B variants, identified in patients suffering from hereditary fructose intolerance and expressed as recombinant proteins in E. coli, from which they were purified to homogeneity. The mutant aldolases were all missense variants and could be classified into two principal groups: catalytic mutants, with retained tetrameric structure but altered kinetic properties (W147R, R303W, and A337V), and structural mutants, in which the homotetramers readily dissociate into subunits with greatly impaired enzymatic activity (A149P, A174D, L256P, and N334K). Investigation of these two classes of mutant enzyme suggests that the integrity of the quaternary structure of aldolase B is critical for maintaining its full catalytic function.

Hereditary fructose intolerance

Hereditary fructose intolerance (HFI, OMIM 22960), caused by catalytic deficiency of aldolase B (fructose-1,6-bisphosphate aldolase, EC 4.1.2.13), is a recessively inherited condition in which affected homozygotes develop hypoglycaemic and severe abdominal symptoms after taking foods containing fructose and cognate sugars. Continued ingestion of noxious sugars leads to hepatic and renal injury and growth retardation; parenteral administration of fructose or sorbitol may be fatal. Direct detection of a few mutations in the human aldolase B gene on chromosome 9q facilitates the genetic diagnosis of HFI in many symptomatic patients. The severity of the disease phenotype appears to be independent of the nature of the aldolase B gene mutations so far identified. It appears that hitherto there has been little, if any, selection against mutant aldolase B alleles in the population: in the UK, approximately 1.3% of neonates harbour one copy of the prevalent A149P disease allele. The ascendance of sugar as a major dietary nutrient, especially in western societies, may account for the increasing recognition of HFI as a nutritional disease and has shown the prevalence of mutant aldolase B genes in the general population. The severity of clinical expression correlates well with the immediate nutritional environment, age, culture, and eating habits of affected subjects. Here we review the biochemical, genetic, and molecular basis of human aldolase B deficiency in HFI, a disorder which responds to dietary therapy and in which the principal manifestations of disease are thus preventable.

Neonatal screening for hereditary fructose intolerance: frequency of the most common mutant aldolase B allele (A149P) in the British population

Hereditary fructose intolerance (HFI) causes severe and sometimes fatal metabolic disturbances in infants and children but responds to dietary treatment. To determine the practicability of screening newborn infants for HFI, we have investigated the frequency of the most common and widespread mutant allele of aldolase B, A149P, in the neonatal population. The polymerase chain reaction was used to amplify aldolase B exon 5 genomic sequences in DNA present in dried blood specimens preserved on Guthrie cards. The A149P mutation was identified by discriminatory hybridisation to allele specific oligonucleotides and confirmed independently by digestion with the restriction endonuclease BsaHI. Twenty-seven A149P heterozygotes were identified by the molecular analysis of aldolase B genes in blood samples obtained from a random cohort of 2050 subjects born in 1994 and 1995, 1.32 +/- 0.49% (95% confidence level). Although no A149P homozygotes were identified, the data allow the frequency of 1 in 23,000 homozygotes for this allele to be predicted. Our findings have implications for establishing an interventional mass screening programme to identify newborn infants with HFI in the UK.

Molecular basis of hereditary fructose intolerance in Italy: identification of two novel mutations in the aldolase B gene

We screened the aldolase B gene in 14 unrelated Italian patients with hereditary fructose intolerance (HFI), and found two novel disease related mutations: a single nucleotide deletion in exon 2 (delta A20) that leads to an early stop codon, and a C-->T transition in exon 8 that substitutes an Arg with a Trp residue at codon 303 (R303W).

Molecular basis of hereditary fructose intolerance: mutations and polymorphisms in the human aldolase B gene

Mutations in the human aldolase B gene that result in hereditary fructose intolerance have been characterized extensively. Although the majority of subjects have been from northern Europe, subjects from other geographical regions and ethnic groups have been identified. At present 21 mutations have been reported; 15 of these are single base substitutions, resulting in nine amino acid replacements, four nonsense codons, and two putative splicing defects. Two large deletions, two four-base deletions, a single-base deletion, and a seven-base deletion/one-base insertion have been found. This last mutation leads to a defect in splicing and it is likely that one of the small deletions does as well. Regions of the enzyme where mutations have been observed recurrently are encoded by exons 5 and 9. Indeed, the three most common mutations are found in these exons. Two of these prevalent HFI mutations arose from a common ancestor and spread throughout the population by genetic drift. This finding was based on linkage to two sequence polymorphisms, which are among very few informative polymorphic markers that have been identified within the aldolase B gene. Because of the prevalence of a few HFI alleles, and the recent advances in molecular methods for identifying and screening for mutation, the diagnosis of HFI by molecular screening methods should become routine. These molecular diagnostic methods will be extremely beneficial for this often difficult to diagnose and sometimes fatal disease.

Null alleles of the aldolase B gene in patients with hereditary fructose intolerance

We report three new mutations in the gene for aldolase B that are associated with hereditary fructose intolerance (HFI). Two nonsense mutations create opal termination codons: R3op (C-->T, Arg3-->ter, exon 2) was found in homozygous form in four affected members of a large consanguineous Turkish pedigree and R59op (C-->T, Arg59-->ter, exon 3) was found on one allele in a woman of Austrian origin known to harbour one copy of the east European mutation, N334K (Asn334-->Lys). The third mutation occurred in a French HFI patient known to be heterozygous for the widespread mutation, A174D (Ala174-->Asp): a single mutation, G-->A, in the consensus acceptor site 3' of intron 6 was found on the remaining allele. These mutations are predicted to abrogate synthesis of functional protein and thus represent null alleles of aldolase B. The mutant alleles can be readily detected in the amplification refractory mutation system (ARMS) or (for R59op and 3' intron 6) by digestion of amplified genomic fragments with DdeI or A1wNI, respectively, to facilitate direct diagnosis of HFI by molecular analysis of aldolase B genes.

The molecular basis of hereditary fructose intolerance in Italian children

We investigated the molecular defects of the aldolase B gene in five unrelated patients affected by hereditary fructose intolerance. The techniques used were DNA amplification, direct sequencing and allele-specific oligonucleotide (ASO) hybridization. The most frequent substitutions found in the hereditary fructose intolerance alleles analysed were the A174D and the A149P mutations, which account for 50% and 30% of the alleles, respectively. In two unrelated families, we found a rare mutation, the MD delta 4 previously described only in one British family, which may be an important cause of the disease in Italy.

The polymerase chain reaction. Applications in dermatology

Within the space of the last 5 years, application of the revolutionary in vitro method of deoxyribonucleic acid (DNA) amplification known as the polymerase chain reaction (PCR), has become ubiquitous. The rapidly increasing number of clinical and research articles utilizing this technology, both in the dermatologic and general medical literature, requires one to have at least a basic understanding of how the PCR is conducted, what it has to offer, and the potential shortcomings. Such knowledge will hopefully allow a more critical appraisal of an increasingly complex literature. This review aims to describe the methodology and medical applications of this powerful technique with special consideration to the increasing role PCR may have on dermatologic research and practice.