ONLINE MUTATION REPORT Molecular analysis of the aldolase B gene in patients with hereditary fructose intolerance from Spain

Hereditary fructose intolerance (HFI) is an autosomal recessive metabolic disorder caused by aldolase (fructosediphosphate aldolase, EC 4.1.2.13) B deficiency. The B isoform of aldolase is critical for the metabolism of exogenous fructose by the liver, kidney, and intestine, since it can use fructose-1-phosphate as substrate at physiological concentrations, unlike aldolases A and C. Affected subjects suffer abdominal pain, vomiting, and hypoglycaemia after the ingestion of fructose, sucrose, or sorbitol. Continued ingestion of noxious sugars causes hepatic and renal injury, which eventually leads to liver cirrhosis and sometimes death, particularly in small infants. Treatment consists of strict elimination of fructose, sucrose, and sorbitol from the diet immediately after HFI is suspected. This diet exclusion therapy allows for a rapid recovery and, if liver and kidney damage is not irreversible, an uneventful course thereafter. Confirmatory diagnosis is generally made by intravenous fructose tolerance tests and assays of aldolase B activity in hepatic biopsies. Since the gene coding for human aldolase B (ALDOB) was cloned, at least 22 different mutations associated with HFI have been described. 4 Kinetic analyses of recombinant aldolase B mutants and molecular modelling studies have shown important structure-function implications for several aldolase B residues affected by HFI mutations. The first HFI mutation identified, termed A149P, is a G→C transversion at the first base of codon 149, which replaces the normal alanine by a proline residue. This missense mutation accounts for more than 50% of mutant alleles in HFI patients from different populations world wide; the frequency of heterozygous carriers in the United Kingdom has been estimated to be 1.32 ± 0.49%, which allows the prediction of an incidence of HFI associated with the A149P allele of 1 in 23 000 births. The three more common aldolase B mutations, A149P, A174D, and N334K, account for more than 80% of HFI alleles in populations from European countries. 11 Although there are many reports dealing with the identification of aldolase B mutations associated with HFI in different European populations, studies on the incidence of these mutations in Spanish subjects have not been reported. In this work, we have analysed the molecular defects in the ALDOB gene in 28 HFI patients from Spain. For this purpose, we have performed PCR amplification of the aldolase B coding exons from the probands and subsequent analysis by restriction endonuclease digestion, allele specific oligonucleotide (ASO) hybridisation, and direct sequencing. Our results have allowed us to estimate the frequencies of HFI alleles in Spanish patients, as well as to discover two novel mutations in the ALDOB gene (g.4271C>G and g.1133G>A) that can cause HFI.