When Less Is More: Phosphate Homeostasis Insights from a Microvillus Inclusion Disease Patient
Bibliographic record
Abstract
Introduction: Microvillus inclusion disease (MVID) is a rare, severe congenital secretory diarrhea caused by recessive MYO5B or STX3 mutations. Multiple cases of MVID with partial proximal tubule (PT) defects are reported (mostly hyperphosphaturia). While MYO5B is expressed in PT cells, MVID patients have normal PT brush border on kidney biopsy, and the PT defect resolves after intestinal transplant. Therefore, it is unlikely that the MYO5B genotype is causally related to the proximal tubulopathy. Case Description: Like all patients diagnosed with MYO5B-MVID, our patient required cycled total parenteral nutrition (TPN). She was referred to nephrology at age 2 for persistent hypophosphatemia despite escalating TPN phosphate (PO4) content, and nephrocalcinosis. Urinary PO4 wasting was confirmed given the low (<65%) tubular reabsorption of phosphate (TRP). FGF-23 and PTH were elevated. A 24 hr balance study (on/off TPN) revealed that TRP was lowest and FeNa highest (˜2%) while on TPN (these values were improved after 6h without TPN). It also confirmed that the negative PO4 balance was only due to renal losses. We hypothesized that high TPN electrolyte concentrations caused an obligate phosphaturic response. Gradual reductions of TPN sodium (Na+) (by 13%), then TPN PO4 (by 70%) over 4 mo led to normalization of serum PO4 (Figure), TRP (83-91%) and FeNa (˜0.3%). Discussion: We propose that excessive TPN Na+ and PO4 promoted a strong phosphaturic response: the combination of several physiologic factors likely explains this unusual phenomenon. Of interest, the intermittently negative TRP suggest that tubular phosphate secretion must have contributed to the massive phosphaturia. A counterintuitive reduction in TPN Na+ and PO4 reduced renal PO4 wasting without impacting serum Na+. We surmise that other MVID cases of PO4 wasting were also probably due to unusually high TPN electrolyte concentrations. Detailed balance studies are invaluable tools to assess complex fluid/electrolyte disorders.
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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 | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.002 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.003 | 0.002 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
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".