Transferrin Isoforms, Old but New Biomarkers in Hereditary Fructose Intolerance

The role of the analysis of sialotransferrin isoforms in the management of hereditary fructose intolerance: a systematic review

Background

Untreated patients affected by hereditary fructose intolerance (HFI) present an abnormal transferrin (Tf) glycosylation pattern suggestive of N-hypoglycosylation. Analysis of defects in N-glycosylation is possible by analysis of serum sialotransferrin (sialoTf) pattern. The sialoTf profile is a valuable tool to facilitate the diagnosis of HFI. Its role in the monitoring of the diagnosed patients is less clear and debating.

Objectives and methods

We examined the literature for the role of profile of serum sialoTf isoforms in monitoring HFI patients aiming at (1) providing an up-to-date summary of the available evidences on the impact of sialoTf isoforms in the follow-up of HFI patients; 2) evaluating the multifactorial effect of genotype and age at diagnosis on sialoTf isoforms; 3) assessing the relation between sialoTf isoforms and long-term liver complications. We used the GRADE approach to rank the quality of evidence.

Results

Nine full papers were identified according to our search criteria. Elevated serum carbohydrate-deficient Tf (CDT) fraction, disialoTf and tetrasialoTf/disialoTf ratio, and the asialoTf, tetrasialoTf and pentasialoTf + hexasialoTf isoforms appeared as the most reliable indicators for a follow up. No clear statistical correlation links sialoTf isoforms and liver damage. Age at diagnosis, potentially related to fructose tolerance, does not overtly impact sialoTf isoforms. Strong genotype-phenotype correlation has not been found so far.

Conclusions

There is no consensus about which isoform of sialoTf is more valuable for monitoring HFI patients. No clear correlation links sialoTf isoforms and liver damage, fructose tolerance and genotype. More robust studies are needed to provide conclusive results.

Aldolase B Deficient Mice Are Characterized by Hepatic Nucleotide Sugar Abnormalities

Hereditary fructose intolerance (HFI) is characterized by liver damage and a secondary defect in N-linked glycosylation due to impairment of mannose phosphate isomerase (MPI). Mannose treatment has been shown to be an effective treatment in a primary defect in MPI (i.e., MPI-CDG), which is also characterized by liver damage. Therefore, the aims of this study were to determine: (1) hepatic nucleotide sugar levels, and (2), the effect of mannose supplementation on hepatic nucleotide sugar levels and liver fat, in a mouse model for HFI. Aldolase B deficient mice (Aldob-/-) were treated for four weeks with 5% mannose via the drinking water and compared to Aldob-/- mice and wildtype mice treated with regular drinking water. We found that hepatic GDP-mannose and hepatic GDP-fucose were lower in water-treated Aldob-/- mice when compared to water-treated wildtype mice (p = 0.002 and p = 0.002, respectively), consistent with impaired N-linked glycosylation. Of interest, multiple other hepatic nucleotide sugars not involved in N-linked glycosylation, such as hepatic UDP-glucuronic acid, UDP-xylose, CMP-N-acetyl-beta-neuraminic acid, and CDP-ribitol (p = 0.002, p = 0.003, p = 0.002, p = 0.002), were found to have altered levels as well. However, mannose treatment did not correct the reduction in hepatic GDP-mannose levels, nor was liver fat affected. Aldob-/- mice are characterized by hepatic nucleotide sugar abnormalities, but these were not abrogated by mannose treatment. Future studies are needed to identify the underlying mechanisms responsible for the abnormal hepatic nucleotide sugar pattern and intrahepatic lipid accumulation in HFI. Trial Registration: PCT ID: PCTE0000340, this animal experiment is registered at (https://preclinicaltrials.eu/).

Development of tools to facilitate the diagnosis of hereditary fructose intolerance

Although hereditary fructose intolerance (HFI) is an inborn error of fructose metabolism that classically presents at infancy, the diagnosis is often missed or delayed. In this study, we aimed to develop tools to facilitate the diagnosis of HFI. The intake of fructose-containing food products, that is, fruit, fruit juice and sugar-sweetened beverages, was assessed by a 3-day food diary in adult HFI patients (n = 15) and age, sex, and BMI-matched controls (n = 15). Furthermore, glycosylation of transferrin was examined using high-resolution mass spectrometry and abnormally glycosylated transferrin was expressed as ratio of normal glycosylated transferrin. We found that the sensitivity and specificity of the 3-day food diary for the intake of at least one fructose-containing food product were both 100%. Both mono-glyco:diglyco transferrin and a-glyco+mono-glyco:di-glyco transferrin were greater in HFI patients and had a high-discriminatory power (area under the receiver operating characteristic curve: 0.97 and 0.94, respectively). In this well-characterized cohort of adult HFI patients, the 3-day food questionnaire and the glycosylation pattern of transferrin are valuable tools to facilitate the recognition and diagnosis of HFI in adult patients.

Estimation of hereditary fructose intolerance prevalence in the Chinese population

Background

Hereditary fructose intolerance (HFI) caused by aldolase B reduction or deficiency that results in fructose metabolism disorder. The disease prevalence in the Chinese population is unknown, which impedes the formulation of HFI screening and diagnosis strategies.

Materials and methods

By searching a local cohort (Chinese Children’s Rare Disease Genetic Testing Clinical Collaboration System, CCGT) and public databases (ClinVar and Human Gene Mutation Database) and reviewing HFI-related literature, we manually curated ALDOB pathogenic or likely pathogenic (P/LP) variants according to ACMG guidelines. Allele frequency (AF) information from the local database CCGT and the public databases HuaBiao and gnomAD for ALDOB P/LP variants was used to estimate and the HFI prevalence in the Chinese population and other populations by the Bayesian framework. We collected the genotype and clinical characteristics of HFI patients from the CCGT database and published literature to study genotype–phenotype relationships.

Result

In total, 81 variants of ALDOB were curated as P/LP. The estimated Chinese HFI prevalence was approximately 1/504,678, which was much lower than that for non-Finland European (1/23,147), Finnish in Finland (1/55,539), admixed American (1/132,801) and Ashkenazi Jewish (1/263,150) populations. By analyzing the genetic characteristics of ALDOB in the Chinese population, two variants (A338V, A338G) had significantly higher AFs in the Chinese population than in the non-Finland European population from gnomAD (all P values < 0.05). Five variants (A150P, A175D, N335K, R60*, R304Q) had significantly lower AFs (all P values < 0.1). The genotype–phenotype association analyses were based on 68 reported HFI patients from a literature review and the CCGT database. The results showed that patients carrying homozygous variant sites (especially A150P) were more likely to present nausea, and patients carrying two missense variant sites were more likely to present aversion to sweets and fruit (all P values < 0.05). Our research reveals that some gastrointestinal symptoms seem to be associated with certain genotypes.

Conclusion

The prevalence of HFI in the Chinese population is extremely low, and there is no need to add HFI testing to the current newborn screening programs if medical costs are considered. A genetic testing strategy is suggested for early diagnosis of HFI.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-022-02487-3.

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.