# Video research-update insert: Phenylalanine accumulation in PAH deficiency

Editorial script and storyboard insert, 5 October 2026. No rendered video. Read alongside the original review; no new grade is announced.

## Narration

Early exposure and early treatment support phenylalanine-related developmental injury in PKU. Adult challenge experiments, brain transport and discordant untreated outcomes refine vulnerability and reversibility; biochemical lowering and neurocognitive recovery remain separate endpoints.

In the 1974 study, earlier treatment was associated with better intellectual outcomes. Nonrandomized developmental treatment comparison; family and timing factors require attention. [P4140266]

In the 2010 study, higher phenylalanine impaired sustained attention and mood in the tested adults. Short challenge in early-treated adults does not measure irreversible childhood injury. [P21153445]

In the 2026 study, sisters had strikingly different cognitive outcomes despite similar tested biochemical/genetic features. A rare discordant pair identifies an unresolved modifier rather than reversing population-level causation. [P41853686]

The next discriminating question is: What determines individual brain exposure and vulnerability? Blood phenylalanine may imperfectly reflect transport, protective modifiers or prior developmental exposure. Longitudinal brain spectroscopy, genotype and exposure histories in prospectively identified discordant cases; matched ascertainment and independent replication.

The timeline shows selected changes in evidence, not inevitable progress or proof of a single cause. The review’s archived grade remains unchanged; the depth of source reading is documented in the update.

## Storyboard and source locks

| Insert | Visual | Narration anchor | Sources |
|---|---|---|---|
| Opening | Claim and bounded update statement | First paragraph | Review claim and source ledger |
| Timeline 1974 | Dated study card with design, result and limit | Earlier treatment was associated with better intellectual outcomes. | [P4140266](https://pubmed.ncbi.nlm.nih.gov/4140266/) |
| Timeline 2010 | Dated study card with design, result and limit | Higher phenylalanine impaired sustained attention and mood in the tested adults. | [P21153445](https://pubmed.ncbi.nlm.nih.gov/21153445/) |
| Timeline 2026 | Dated study card with design, result and limit | Sisters had strikingly different cognitive outcomes despite similar tested biochemical/genetic features. | [P41853686](https://pubmed.ncbi.nlm.nih.gov/41853686/) |
| G1 | Question → competing explanation → discriminating test | What determines individual brain exposure and vulnerability? | [P9809507](https://pubmed.ncbi.nlm.nih.gov/9809507/), [P10207169](https://pubmed.ncbi.nlm.nih.gov/10207169/), [P41853686](https://pubmed.ncbi.nlm.nih.gov/41853686/) |
| G2 | Question → competing explanation → discriminating test | Which adult domains change reversibly over which time scale? | [P21153445](https://pubmed.ncbi.nlm.nih.gov/21153445/), [P38569786](https://pubmed.ncbi.nlm.nih.gov/38569786/), [P29331172](https://pubmed.ncbi.nlm.nih.gov/29331172/) |
| G3 | Question → competing explanation → discriminating test | Which mediator carries developmental versus adult effects? | [P10207169](https://pubmed.ncbi.nlm.nih.gov/10207169/), [P29331172](https://pubmed.ncbi.nlm.nih.gov/29331172/), [P4140266](https://pubmed.ncbi.nlm.nih.gov/4140266/) |
| G4 | Question → competing explanation → discriminating test | Do newer lowering strategies improve durable neurocognitive outcomes? | [P17693179](https://pubmed.ncbi.nlm.nih.gov/17693179/), [P29628378](https://pubmed.ncbi.nlm.nih.gov/29628378/), [P21153445](https://pubmed.ncbi.nlm.nih.gov/21153445/) |

## Editorial constraints

- Use the primary-source links shown above and keep the inference limit on screen with each milestone.
- Do not narrate an abstract check as complete-paper examination, a model result as human proof, or an unresolved inference as absence of all research.
- Preserve trial endpoint hierarchy, cohort reuse, correction notices and online/issue dates.
- Use original graphics made from this ledger. Publisher figure imagery has not been cleared or supplied for video reuse.
- Confirm any change in verdict through a separate documented HSEF review; this insert makes none.