Congenital Nemaline Myopathy: The Value of Magnetic Resonance Imaging of Muscle
Bibliographic record
Abstract
Nemaline myopathy is a clinically and genetically heterogenous disorder that may present from birth to late adulthood.Patients with nemaline myopathy exhibit weakness of proximal muscles (particularly neck flexors) and, in the case of younger children, facial, bulbar, and/or respiratory muscle weakness.Nemaline myopathy can be classified according to age of symptom onset and disease severity.1 It has been linked to nine genes: NEB, ACTA1, TPM2, TPM3, TNNT1, CFL2 and less commonly; KLH40, KLH41, and KBTBD13.The classic features seen on muscle biopsy include sarcoplasmic rodlike structures on microscopic study using Gomori trichrome stain.Electron microscopy also classically demonstrates electron-dense nemaline bodies associated with sarcomeric Z-lines and less commonly intranuclear inclusions.Skeletal muscle alpha-actin (ACTA1) is the principal actin isoform of skeletal muscle.It forms the thin filament of the sarcomeric unit and interacts most notably with myosin to generate muscle contraction.Mutations within ACTA1 are the second most common cause of nemaline myopathy (after NEB mutations) accounting for about 20%-30% of cases. 2 Most ACTA1 mutations are thought to be de novo, although autosomal dominant and recessive inheritance has been reported.2 We provide a clinical summary of an infant who presented with failure to thrive and tachypnea and who was later diagnosed with a nemaline myopathy.We illustrate the value of MRI in this case at assisting with the selection of muscle to biopsy.Genetic testing subsequently confirmed a mutation in an ACTA1 gene.Clinical follow-up was favourable as with adequate nutrition and bilevel positive airway pressure ventilation support the patient demonstrated appropriate gross motor development at his most recent clinical follow-up at 21 months old. CASEA 4-month-old boy presented to the emergency room for failure to thrive over the preceding 2 months.He was born at 37 weeks' gestational age to a healthy mother.Pregnancy was unremarkable.Antenatal ultrasounds were reassuring with no polyhydramnios.Delivery was via a planned Caesarean section with no resuscitation required.His birth weight was 3.32 kg (75th %ile).He established bottle-feeding without difficulty and was discharged home.His mother reported a gradual increase in fatigue with feeding, poor weight gain, and rapid breathing over at least 2 months.Physical examination showed an alert infant with tachypnea, mild intercostal indrawing, and abdominal breathing.No dysmorphic features were apparent.His weight was 4.59 kg
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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 | 0.004 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.002 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.002 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.004 | 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".