Chapter 66: Polycystic Kidneys

Patient Story

A 17-year-old boy is seen in the office with mild abdominal pain and blood in his urine noticed after playing football with his friends. Exam is significant only for left flank tenderness and his vital signs, including blood pressure, are normal. His urine tests positive for blood (3+) and 1+ protein; microscopic urinalysis reveals numerous red blood cells but no white blood cells or casts. On further questioning, his mother reports that the boy’s father and paternal aunt have some type of “kidney problem” but she and his father have been divorced for many years and he rarely sees his father. An ultrasound reveals bilateral enlarged kidneys with multiple cysts and a calculus in the left kidney. A CT scan confirms the diagnoses (Figure 66-1).

Introduction

Polycystic kidney disease (PKD) is a manifestation of a group of inherited disorders resulting in renal cyst development. In the most common form, autosomal-dominant polycystic kidney disease (ADPKD), extensive epithelial-lined cysts develop in the kidney; in some cases, abnormalities also occur in the liver, pancreas, brain, arterial blood vessels, or a combination of these sites. In autosomal recessive polycystic disease (ARPKD), the disease primarily causes enlarged cystic kidneys and hepatic fibrosis and usually presents in infancy. The cysts in ARPKD form only in the collecting tubule and are smaller and typically not visible on gross examination.

Epidemiology

• Most common tubular disorder of the kidney, affecting 1 in 300 individuals.

• Autosomal dominant in 90 percent of cases.¹ The majority of cases of ADPKD are diagnosed in adults but can be diagnosed at any age.² In a German population study, the overall prevalence of ADPKD was 32.7/100,000 reaching a maximum of 57.3/100,000 in the 6th decade of life.³

• Sporadic mutation in approximately 1:1000 individuals.

• ADPKD accounts for approximately 5 to 10 percent of cases of end-stage renal disease (ESRD) in the US.

• ADPKD is most frequently seen in the third and fourth decades of life, but can be diagnosed at any age.

• ARPKD is estimated to occur in 1:10,000 to 1:40,000 live births, although this may be an underestimate as severely affected neonates do not survive beyond the first few days of life and may not be correctly diagnosed.²

• Both diseases are seen in all races and ethnicities and affect males and females equally.

Etiology and Pathophysiology

• ADPKD results from mutations in either of 2 genes that encode plasma membrane–spanning polycystin 1 (PKD1) and polycystin 2 (PKD2).⁴ Polycystins regulate tubular and vascular development in the kidneys and other organs (liver, brain, heart, and pancreas). PKD1 and PKD2 are colocalized in primary cilia and appear ...