Question

Consider the following:

1. Cystinuria
2. Cystinosis
3. Hartnup's disease
4. Renal glycosuria

Disorders of amino acid transport include

• A. 1 and 2
• B. 1 and 3
• C. 2, 3 and 4
• D. 1, 2, 3 and 4

Hint:

Think of this as one family of inherited solute-transporter defects, not separate unrelated diseases.

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question lists four inherited conditions and asks which combination represents disorders of amino acid transport, testing knowledge of inherited renal tubular and intestinal transport defects.

Step 2: Key Concept or Approach:
A group of inherited conditions result from defective transport proteins in the proximal renal tubule and, in some cases, the intestinal brush border. Cystinuria is a defect in the transporter for dibasic amino acids (cystine, ornithine, lysine, arginine). Hartnup's disease is a defect in the transporter for neutral amino acids, especially tryptophan. Cystinosis is a defect in the lysosomal membrane transporter cystinosin, which normally exports cystine out of lysosomes, and it is grouped with the other cystine-related transport disorders because of its shared substrate. Renal glycosuria is a defect of the tubular glucose transporter, and in classic teaching on inherited renal tubular transport disorders it is discussed alongside the aminoacidurias because all four share the common mechanism of an isolated, otherwise-healthy tubule failing to reabsorb a specific solute.

Step 3: Working Through the Options:
"1 and 2" is incomplete because it leaves out Hartnup's disease, a well-established amino acid transport defect. "1 and 3" is incomplete because it leaves out both cystinosis and renal glycosuria. "2, 3 and 4" is incomplete because it leaves out cystinuria, the prototype amino acid transport disorder. "1, 2, 3 and 4" captures the full group of inherited solute transport disorders referenced by the question -- cystinuria and Hartnup's disease as classic amino acid transporter defects, cystinosis as a cystine transport defect, and renal glycosuria as the corresponding glucose transport defect grouped with them in this classification.

Step 4: Conclusion:
The correct answer is 1, 2, 3 and 4, all four conditions together.