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

Abstract

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.

Fig. 1

Allele-specific oligonucleotide dot-blot analysis performed on four American HFI patients. Panel A: The proband and parents denoted by the pedigree and control DNAs were screened for the presence of the A337V mutant allele. Wild-type (A337) and mutant (A337V) ASOs (10 ng) were 5′-end labeled with [γ-³²P]ATP and hybridized to blots containing 100 ng of exon 9 PCR-amplified genomic or control plasmid (Wt and Mut) DNA. Blots were washed at 67°C and 65°C, respectively, and exposed for 1 d and 7 d, respectively. Panel B: Three patients were screened for the presence of the R59Op and Δ4E4 mutant alleles. Wild-type and mutant ASOs for each allele as noted on the left were 5′-end labeled with [γ-³²P] ATP and hybridized to 100 ng of exon 3 (patients 1 and 3) or exon 4 (patients 2 and 3) PCR-amplified genomic or control plasmid (Wt and Mut) DNA. Blots were washed at 66°C and blots exposed for 1 d (R59, R59Op, E4) or 5 h (Δ4E4)