cystinuria

Introduction

3 types of cystinuria:

• Type 1 (fully recessive or silent)
• Type 2 (high excretor)
• Type 3 (moderate excretor)

Pathology

• intestinal & renal tubular transport disorder (reduced absorption) of dibasic amino acids:
  • C cystine
  • O ornithine
  • L lysine
  • A arginine
• cystine is the least soluble in normally acidic urine & tends to precipitate
• homozygotes develop urolithiasis

Genetics

• autosomal recessive
• mutation in the gene for SLC3A1 (type 1)
• mutation in the gene for SLC7A10
• mutation in the gene for SLC7A9

Clinical manifestations

• nephrolithiasis (cystine stones)
• short stature

Laboratory

• urinalysis
  • cystine crystalluria
  • positive nitroprusside test

Management

• stones can be dissolved with:
  • urinary alkalinization
  • high take of fluids
  • maintain urine pH at 7
• chelating agents may be useful
  • D-penicillamine or tiopronin
  • captopril if hypertension
• pyridoxine (vitamin B6) 25 mg PO QD
• potassium citrate as inhibitor of stone formation
• low protein diet
• restrict dietary sodium

More general terms

• genetic disease of the kidney
• inborn error of metabolism

Additional terms

• cystine
• cystine in urine
• hypotonia-cystinuria syndrome

Database

• OMIM: https://mirror.omim.org/entry/104614
• OMIM: https://mirror.omim.org/entry/220100