Down Syndrome and Aneuploidies

A 3-month-old boy born to a 38-year-old mother is brought to the pediatric clinic for developmental assessment. On examination, he has a broad flat face, upslanting palpebral fissures, a single palmar crease, and low-set ears. Cardiac auscultation reveals a systolic murmur. Developmental milestones are delayed. Karyotype analysis shows 47,XY,+21. Which of the following cardiac lesions is MOST commonly associated with this condition?

Which clinical feature best distinguishes Down syndrome (trisomy 21) from Edwards syndrome (trisomy 18)?

What is the recurrence risk for Down syndrome (Trisomy 21) in a subsequent pregnancy when the mother is a balanced translocation carrier (14;21)?

A 2-year-old girl with Down syndrome is brought to the pediatric outpatient clinic for routine follow-up. Her parents report she has been increasingly irritable over the past 3 months, with poor feeding and constipation. Physical examination reveals a firm, enlarged thyroid gland. Laboratory investigations show TSH 8.2 mIU/L (normal 0.5–5.0) and free T4 2.1 ng/dL (normal 0.8–1.8). What is the most appropriate next step in management?

A 3-year-old child with Down syndrome is being evaluated for associated anomalies. Which of the following is NOT typically associated with trisomy 21?