## Core Concept
Nephrotic syndrome in children is characterized by significant proteinuria, hypoalbuminemia, hyperlipidemia, and edema. The most common cause in children is minimal change disease. Understanding the typical presentation, diagnostic approach, and treatment options for nephrotic syndrome in children is crucial.

## Why the Correct Answer is Right
- **Statement 1:** Minimal change nephrotic syndrome indeed accounts for approximately 80-85% of cases in children, making it the most common cause of nephrotic syndrome in this age group.
- **Statement 2:** A serum albumin level below 2.5 g/dl is a diagnostic criterion for nephrotic syndrome, which is characterized by significant hypoalbuminemia.
- **Statement 3:** While cyclosporine and azathioprine are used in the treatment of nephrotic syndrome, especially in cases that are steroid-dependent or frequently relapsing, the mainstay of initial therapy is corticosteroids, not these immunosuppressive agents.
- **Statement 4:** Pretreatment biopsy is not routinely done in all cases of nephrotic syndrome in children. Given the high prevalence of minimal change disease, a therapeutic trial of corticosteroids is often used as both a diagnostic and therapeutic tool. Biopsy is considered in cases with atypical presentations or when there is a poor response to initial therapy.

## Why Each Wrong Option is Incorrect
- **Option A:** This option suggests that all statements are true, which is incorrect based on the explanation above, particularly regarding the mainstay of therapy and the routine use of pretreatment biopsy.
- **Option B:** This option would imply that only statements 1 and 2 are true, which underrepresents the complexity of the treatment (statement 3) and overrepresents the necessity of biopsy (statement 4).
- **Option D:** Suggesting only statement 4 is false does not accurately reflect the inaccuracies in statements 3 and 4.

## Clinical Pearl / High-Yield Fact
A key point to remember is that minimal change disease is the most common cause of nephrotic syndrome in children, and the initial treatment is usually a corticosteroid. The use of immunosuppressive agents like cyclosporine and azathioprine is reserved for specific cases. Additionally, not all children with nephrotic syndrome require a renal biopsy before starting treatment.

## Correct Answer: B.