Antenatal Biochemical Expression of Cystinuria and Relation to Fetal Hyperechogenic Colon

Cystinuria is an inherited disorder characterized by impaired apical transport of cystine and dibasic amino acids (e.g., ornithine, lysine, and arginine) in the renal proximal tubule and the small intestine epithelia. The overall estimated prevalence is 1/7000 neonates (1). Because of impaired renal cystine reabsorption, cystine precipitates and forms calculi that can produce urinary tract obstruction and may lead to renal insufficiency. Cystinuria is responsible for ∼10% of all kidney stones observed in children; in ∼50% of patients, stones form in the first decade of life. Diagnosis allows introduction of therapy to reduce stone formation and risk of renal impairment. Prenatal biochemical expression of the disease has not been described. Fetal hyperechogenic small bowel (FHB), an infrequent ultrasound finding (0.1%–1.8% of pregnancies), is associated with severe fetal diseases such as cystic fibrosis and trisomy 21 (2). Even less common is fetal hyperechogenic colon (FHC) in which the hyperechogenicity is strictly limited to the colon. Recently, it has been suggested that FHC could be associated with cystinuria(3). We found biochemical prenatal evidence of cystinuria and confirmed the association of cystinuria with …