A Single Mutation Inside the NPA Motif of Aquaporin-1 Found in a Colton-Null Phenotype

8 untranslated region, exons 1 and 2, as well as intron 1 and part of intron 2 was amplified by polymerase chain reaction (PCR). Amplification primers were based on the L-ferritin sequence published by Santoro et al 4 (GenBank accession no. X03742). DNA fragments were subsequently cloned and more than 10 clones from each patient were sequenced by automated DNA sequencing. Sequence analysis identified a point mutation, C to T, at position 33, according to the numbering of Cazzola et al, 5 in a half of the analyzed clones of all patients as an average (GenBank accession no. AF117958). This nucleotide substitution is located at the consensus three nucleotide bulge structure, positions 31-33 (Fig 2). Correlation between genotype and phenotype has been suggested for HHCS.5 Mutations placed at the conserved loop are associated to higher ferritin concentrations and more severe cataracts than those found in the three-nucleotide motif forming the IRE bulge. Furthermore, nucleotide changes located at the lower stem have been associated with asymptomatic cataract and serum ferritin levels in the range of 350 to 650 μg/L. Therefore, three nucleotide substitutions have been described at the IRE bulge motif. The mutation termed Pavia 1, G to A at position 32, was associated with similar serum ferritin levels to those found in our studied family and a similar mild cataract with visual symptoms appearing during childhood. 5 More recently, two French families have been described bearing the same G to T substitution at position 32, though displaying a marked variability in the age of onset of cataract between members of the two families. 6