What is the most likely diagnosis for a neonate with low set ears, flat occiput, and a double bubble sign on chest X-ray?

The presentation of low set ears, a flat occiput, and a double bubble sign on chest X-ray strongly suggests Down's syndrome. The features listed are classical signs associated with this condition.

Low set ears and a flat occiput are part of the distinct physical characteristics often observed in infants with Down's syndrome, resulting from genetic alterations involving chromosome 21. The double bubble sign typically indicates duodenal atresia, a condition that is significantly associated with Down's syndrome, as these infants have an increased risk for gastrointestinal anomalies.

In summary, the combination of these physical signs and the double bubble finding on X-ray aligns with the diagnostic criteria for Down's syndrome, enhancing the confidence in this diagnosis.