GK

GK is required for the first step of galactose metabolism, and its loss causes galactokinase deficiency (PMID:10521295). A founder missense mutation in GK1 (P28T), replacing a conserved proline at position 28 with threonine, was mapped to chromosome 17q in Roma (Gypsy) families and identified as the causative allele underlying early-childhood cataract formation (PMID:10521295). Beyond this genetic mapping and mutation identification, no further mechanistic detail—including in vitro enzymatic characterization of the variant—has been characterized in the available corpus.

1. 1999 Medium

   Establishing the genetic basis of galactokinase deficiency answered which gene and which lesion abolish the first step of galactose metabolism in an affected population.

   Evidence Genetic linkage mapping to chromosome 17q, radiation hybrid mapping, and haplotype analysis identifying the P28T founder mutation in Roma families

   PMID:10521295

   Open questions at the time

   • No in vitro enzymatic reconstitution confirming that P28T abolishes galactokinase catalytic activity
   • Structural consequence of the P28 proline substitution not determined
   • Mechanism linking enzyme loss to cataract formation not directly tested

• How the P28T substitution disrupts the enzyme at the biochemical and structural level, and how loss of galactose phosphorylation mechanistically drives cataractogenesis, remains unresolved in the available corpus.
• No enzymatic kinetics for wild-type or mutant protein in the corpus
• No structural model of the substrate-binding region affected by P28
• No cellular or tissue-level mechanism connecting metabolite accumulation to lens pathology