A neonate born to a 38-year-old primigravida at 38 weeks gestation presents with characteristic dysmorphic features including upslanting palpebral fissures, epicanthal folds, a flat nasal bridge, and hypotonia. On examination of the palms, the structure marked **A** is noted bilaterally. A karyotype confirms trisomy 21. Which of the following best describes the clinical significance of the finding marked **A** in Down syndrome?
A. It is a fragmented palmar crease pattern that correlates with the degree of intellectual disability and requires early neurodevelopmental intervention
B. It is a double palmar crease that indicates a more severe phenotype and is associated with increased risk of congenital heart disease
C. It is a longitudinal palmar crease that reflects abnormal dermatoglyphic development and is pathognomonic for Down syndrome
D. It is a single transverse palmar crease (simian crease) that serves as a major diagnostic clue for trisomy 21, present in approximately 45% of affected individuals and highly suggestive when bilateral
Explanation
Why option 1 is correct
The structure marked A is the single transverse palmar crease (simian crease), a characteristic hand finding in Down syndrome (trisomy 21). According to Nelson Textbook of Pediatrics, this crease is present in approximately 45% of individuals with Down syndrome and is particularly significant when bilateral, serving as a major diagnostic clue alongside other dysmorphic features. The simian crease results from abnormal development of the palmar ridge patterns (dermatoglyphics) and, when present bilaterally in the context of other clinical features (upslanting palpebral fissures, epicanthal folds, flat nasal bridge, hypotonia, and confirmed karyotype 47,XY,+21), strongly supports the diagnosis of trisomy 21.
Why each distractor is wrong
Option 2: A double palmar crease is not a recognized finding in Down syndrome. The characteristic crease in trisomy 21 is a single transverse crease, not a double crease. This option confuses the morphology and is anatomically incorrect.
Option 3: A longitudinal palmar crease is not associated with Down syndrome. The crease in trisomy 21 runs transversely across the palm (hence "transverse palmar crease"), not longitudinally. This represents a fundamental misunderstanding of the dermatoglyphic abnormality.
Option 4: While dermatoglyphic abnormalities in Down syndrome do reflect chromosomal imbalance, the severity of intellectual disability (mean IQ 40–50) does not correlate with the presence or absence of the simian crease. The crease is a structural marker, not a functional predictor of cognitive outcome. This option incorrectly links a static anatomical finding to variable neurodevelopmental severity.
High-YieldNEET PG
The bilateral single transverse palmar crease (simian crease) is present in ~45% of Down syndrome cases and is a major diagnostic clue, especially when bilateral and accompanied by other dysmorphic features and confirmed trisomy 21 on karyotype.
Nelson Textbook of Pediatrics 21e — Down Syndrome (Trisomy 21) section
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