## Why Option 1 is right The structure marked **A** (Brushfield spots) represents focal areas of stromal hyperplasia on the periphery of the iris. They are present in 35–78% of children with Down syndrome (trisomy 21) but are NOT pathognomonic — they also occur in approximately 24% of normal newborns. This makes them a supportive clinical sign that should prompt further investigation (karyotyping, FISH) but cannot diagnose Down syndrome in isolation. The finding is best visualized with slit-lamp examination or penlight magnification and may be less obvious in dark irises, which is relevant in Indian populations where darker iris pigmentation is common. ## Why each distractor is wrong - **Option 2**: Brushfield spots are present in only 35–78% of Down syndrome cases, not >90%, and they are explicitly NOT pathognomonic. They occur in normal newborns, so they cannot warrant karyotyping in isolation. This overstates both the sensitivity and specificity of the sign. - **Option 3**: Brushfield spots represent stromal *hyperplasia*, not atrophy. Additionally, they are not virtually absent in normal children — they appear in ~24% of the general newborn population, making them a non-specific finding. This option reverses the pathology and falsely claims high specificity. - **Option 4**: Brushfield spots are present from birth (or early infancy) and do not develop progressively after 6 months. They are not pigmented nevi but rather areas of stromal proliferation. This option mischaracterizes both the timing and histologic nature of the finding. **High-Yield:** Brushfield spots are a *supportive* sign of Down syndrome (present in ~50% of cases) but are found in ~24% of normal newborns — always correlate with other dysmorphic features and perform karyotyping for confirmation. [cite: Nelson Textbook of Pediatrics 21e Ch 98; Robbins Pathologic Basis of Disease 10e Ch 6]
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