A 38 years old female gives birth at 37 weeks to a small for gestational age female infant. During the pregnancy, foetal ultrasound showed an endocardial cushion defect and polyhydramnios due to duodenal atresia. Karyogram shows chromosomal abnormalities as 47,XX,+21. a. What is your probable diagnosis? b. Write in details about pathogenesis. c. Write all the prenatal investigations to confirm this diagnosis.