OP12.02: Absent nasal bone without other features of Trisomy 21 in pregnant Caucasian women: check the clavicles for cleidocranial dysplasia
Bibliographic record
Abstract
Failed visualisation of the fetal nasal bone is strongly associated with aneuploidies (T21, 13, and 18). It may also rarely be observed in euploid fetuses, mostly of Afro-Caribbean and Asian ethnicities. Absent nasal bone can be the presenting sign for cleidocranial dysplasia. Case report: A 42-year-old pregnant woman was referred at 24 weeks for an absent nasal bone (Fig 1). In addition to this finding, the fontanelles were large with wide sutures (Fig 2), the brain parenchyma was unusually clearly visible, and the clavicles were hypoplastic (Fig 3). Fetal growth was normal. The child's father had two children from a previous relationship who had missing clavicles. The diagnosis of cleidocranial dysplasia was made and confirmed by amniocentesis with detection of RUNX2 gene mutation. Discussion: Cleidocranial dysplasia is an autosomal dominant skeletal dysplasia characterised by abnormal bone and dental development with normal cognitive function. 80% of cases are caused by a mutation in the RUNX2 gene. Prenatal genetic testing for this mutation is available. The prenatal sonographic diagnosis is primarily based on clavicular hypoplasia or aplasia and insufficient ossification of the cranium. In the few published cases, there are occasional references to the absence of the nasal bone, yet in most cases this is retrospective. Absent nasal bone may help to establish the prenatal diagnosis. Prenatal diagnosis is important, since the abnormal ossification of the skull and chest may expose the fetal brain and lungs to potential damage during natural birth. In conclusion, in absence of fetal nasal bone and low risk for fetal aneuploidies or if aneuploidies are excluded, consider cleidocranial dysplasia and check the clavicles.
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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 | 0.002 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.002 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 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".