What are the typical physical features of Down syndrome in a term newborn?

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Physical Features of Down Syndrome in Term Newborns

Virtually all newborns with Down syndrome are hypotonic and display characteristic dysmorphic features including upslanting palpebral fissures, epicanthal folds, flat nasal bridge, Brushfield spots of the iris, shortened incurving fifth finger, and transverse palmar crease 1.

Core Facial and Cranial Features

The craniofacial presentation in term newborns with Down syndrome includes:

  • Flat facial profile with bitemporal narrowness
  • Upslanting palpebral fissures (upward slant of the eyes)
  • Epicanthal folds (skin folds at the inner corner of the eyes)
  • Flat nasal bridge with a short nose
  • Brushfield spots - distinctive speckled iris patterns
  • Full cheeks and abundant neck skin
  • Mouth corners turned downward with protruding tongue
  • Small, dysplastic ears that may be low-set or posteriorly angulated 1, 2

Musculoskeletal and Extremity Features

Key physical findings in the extremities and overall muscle tone:

  • Generalized hypotonia - present in virtually all affected newborns, this is one of the most consistent findings
  • Shortened, incurving fifth finger (clinodactyly)
  • Transverse palmar crease (single palmar crease)
  • Sandal gap deformity - increased space between the first and second toes 1, 3, 2

Clinical Diagnostic Scoring

A validated 8-sign scoring system exists for clinical diagnosis in the first week of life 2:

  1. Abundant neck skin
  2. Mouth corners turned downward
  3. General hypotonia
  4. Flat face
  5. Dysplastic ear
  6. Epicanthic eye-fold
  7. Gap between first and second toes
  8. Protruding tongue

Newborns scoring 6-8 signs are considered clinically proven Down syndrome with high accuracy (no false positives in ~19,000 births studied), while scores of 0-2 effectively exclude the diagnosis 2. Scores of 3-5 represent a heterogeneous group requiring cytogenetic confirmation.

Important Clinical Caveats

The clinical diagnosis accuracy varies significantly by genetic subtype: 90% of trisomy 21 cases and 100% of translocation cases are diagnosed clinically, but only 37.5% of mosaic Down syndrome cases are identified by physical features alone (p < 0.001) 3. This is critical because mosaic cases may lack obvious dysmorphic features and are often missed, yet should always be considered in children with unexplained developmental delays.

Common pitfall: The six most frequent features (simian crease, sandal gap, epicanthic folds, hypotonia, upslanting palpebral fissures, protruding tongue) also appear in karyotypically normal infants with sufficient frequency to cause false clinical suspicion 3. Therefore, chromosome analysis should always be performed to confirm the diagnosis, even when clinical features are highly suggestive.

Associated Findings Requiring Immediate Attention

Beyond the characteristic physical features, be alert for:

  • Congenital heart disease - present in 40% of cases, requiring echocardiography in all newborns 1, 4
  • Duodenal atresia or other gastrointestinal anomalies (5% of cases) - highly specific for Down syndrome when present 1
  • Hematological abnormalities - virtually universal, including thrombocytopenia, polycythemia, and transient abnormal myelopoiesis 5

89.4% of Down syndrome diagnoses occur between days 1-7 of life 3, emphasizing the importance of systematic physical examination of all newborns for these characteristic features in the immediate postnatal period.

References

3
Research

Accuracy of the clinical diagnosis of Down syndrome.

The Ulster medical journal, 2004

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