HowPAH gene mutations cause hyper-phenylalaninemia and why mechanism matters: Insights from in vitro expression
Bibliographic record
Abstract
Mutations in the human PAH gene, which encodes phenylalanine hydroxylase are associated with varying degrees of hyperphenylalaninemia (HPA). The more severe of these manifest as a classic metabolic disease--phenylketonuria (PKU). In vitro expression analysis of PAH mutations has three major applications: 1) to confirm that a disease-associated mutation is genuinely pathogenic, 2) to assess the severity of a mutation's impact, and 3) to examine how a mutation exerts its deleterious effects on the PAH enzyme, that is, to elucidate the molecular mechanisms involved. Data on expression analysis of 81 PAH mutations in multiple in vitro systems is summarized in tabular form online at www.pahdb.mcgill.ca. A review of these findings points in particular to a prevalent general mechanism that appears to play a major role in the pathogenicity of many PAH mutations. Amino acid substitutions promote misfolding of the PAH protein monomer and/or oppose the correct assembly of monomers into the native tetrameric enzyme. The resulting structural aberrations trigger cellular defenses, provoking accelerated degradation of the abnormal protein. The intracellular steady-state levels of the mutant PAH enzyme are therefore reduced, leading to an overall decrease in phenylalanine hydroxylation within cells and thus to hyperphenylalaninemia. There is considerable scope for modulation of the enzymic and metabolic phenotypes by modification of the cellular handling--folding, assembly, and degradation--of the mutant PAH protein. This has major implications, both for our understanding of genotype-phenotype correlations and for the development of novel therapeutic approaches.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.002 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".