Cystinuria

Cystinuria is a genetic disorder typified by buildup of organic chemical compounds in the kidneys, ureter and bladder. ^[1]

Epidemiology

General prevalence is estimated to be 1 per 7,000 people. ^[1] The condition is more common among white persons. Males are more severely affected than females. Reports of stones are more frequent during the second or third decade of life. ^[2]

Causes

Cystinuria is inherited in an autosomal recessive fashion usually involving mutations in the SLC3A1 and SLC7A9 gene. Cystine is a sulfur -containing amino acid which is generally absorbed back in the bloodstream. People who have cystinuria have a transport defect thus cysine cannot be correctly reabsorb which consequently leads to accumulation in the urine. The excessive cystine develops into crystals which later form stones that get stuck usually in the kidneys or bladder. This may result to obstruction along the urinary tract and diminished capacity of the kidneys to eradicate body wastes in the form of urine. Overtime, the situation may also predispose to bacterial infection. ^{[3] [4]}

Signs and Symptoms

The most common presentation is renal colic. This is typically described as sharp intermittent pain in the back, side and groin area. The intensity can range from moderate to severe and the pain is usually noted to travel from front to back by and large becoming worse at night time. ^[5]

Some patients may have blood in the urine. Others may develop urinary tract infection. ^[1]

Diagnosis

Early diagnosis is extremely important to prevent morbidity and death. After getting the patient’s medical history and performing a physical examination, the physician often requests laboratory studies to detect stones. Among the tests available are 24 hour urine collection, urinalysis, intravenous pyelogram and sodium cyanide–nitroprusside test. Imaging studies may include plain radiography of the abdomen and pelvis, renal ultrasonography, intravenous pyelography and CT scan. ^{[1] [3]}

Treatment

Generally, the goal is cystine stone deterrence which is often done through sufficient hydration and urinary alkalinization. Patients are instructed to drink plenty of fluids. Some may be given fluids intravenously. If the initial approach fails, the patient is often prescribed with drugs. Pain relievers may be added if needed. Large stones may require surgical removal. The condition often persists throughout life. Fortunately, it hardly ever leads to kidney failure. ^[3]

References:

1.    http://www.medicinenet.com/cystinuria/article.htm

2.    http://emedicine.medscape.com/article/435678-overview#a0199

3.    http://www.nlm.nih.gov/medlineplus/ency/article/000346.htm

4.    http://global.britannica.com/EBchecked/topic/148835/cystine

5.    http://www.cystinuria.com/symptoms/