Correct Answer: A

Rationale: The correct answer is A: nondisjunction. Trisomy 21, also known as Down syndrome, is caused by nondisjunction, which is an error in cell division leading to an extra copy of chromosome 21. This additional genetic material alters the course of development and causes the characteristics associated with Down syndrome. Choices B, C, and D are incorrect. X-linked recessive inheritance refers to genetic disorders carried on the X chromosome, genomic imprinting involves gene expression based on parental origin, and autosomal dominant inheritance relates to disorders caused by a dominant gene on one of the non-sex chromosomes. In the case of trisomy 21, the cause is specifically related to the error in chromosome division, making nondisjunction the most appropriate answer.

Correct Answer: C

Rationale: The correct dietary instruction for a child with GERD is to avoid high-fat foods. High-fat foods can relax the lower esophageal sphincter, leading to increased reflux. While avoiding gluten may be necessary for individuals with gluten sensitivity or celiac disease, it is not a standard recommendation for GERD. Avoiding spicy foods and dairy products may help some individuals with GERD, but the most crucial dietary advice is to avoid high-fat foods.

Correct Answer: D

Rationale: Recognizing signs of hypoglycemia is essential for managing type 1 diabetes mellitus. Hypoglycemia, which occurs when blood glucose levels drop too low, can be dangerous and requires immediate intervention to prevent severe complications. Monitoring blood glucose levels more frequently than once a day, following a strict meal plan, and administering insulin only when blood glucose is high are important aspects of diabetes management but recognizing signs of hypoglycemia is crucial as it enables prompt action to prevent adverse outcomes.

Correct Answer: B

Rationale: Edema is a hallmark clinical manifestation of nephrotic syndrome. In nephrotic syndrome, there is increased permeability of the glomerular filtration barrier, leading to protein loss in the urine (proteinuria). The decrease in serum protein levels results in a reduced oncotic pressure, leading to fluid shifting from the intravascular space into the interstitial spaces, causing edema. Jaundice (choice A) is not typically associated with nephrotic syndrome. Hypertension (choice C) is more commonly seen in conditions like nephritic syndrome. Polyuria (choice D) is excessive urination and is not a prominent feature of nephrotic syndrome.

Correct Answer: A

Rationale: The correct answer is to advise the parents to avoid exposure to allergens. Asthma attacks are often triggered by allergens such as dust mites, pollen, pet dander, and mold. By minimizing the child's exposure to these triggers, the likelihood of asthma attacks can be reduced. Encouraging regular exercise is beneficial for overall health but may not directly prevent asthma attacks. Providing a high-protein diet and increasing fluid intake are important for general well-being but do not specifically address asthma prevention.