A cyst is a small fluid filled sac. In polycystic kidney disease, a multitude of fluid filled sacs develop in the kidneys.
There are two main types of this disorder that differ in their age of onset. The first type is ADPKD (autosomal dominant polycystic kidney disease), also known as adult type polycystic kidney disease. The second type is called ARPKD (autosomal recessive polycystic kidney disease), also known as infantile type polycystic kidney disease.
This article will discuss each type separately.
What are the symptoms?
ADPKD is the most common type of this disorder. It manifests in a great number of cysts that become enlarged until they affect kidney function around the age of forty to fifty. In many cases, the clusters of cysts begin to affect kidney function only at a later age, but during history only a few cases have been documented in children.
Damage to the kidneys is severe and manifests in kidney failure. In fact, ADPKD is the most common cause of kidney failure during old age.
How is ADPKD inherited?
Two gene mutations can cause ADPKD. The first gene is called APKD1 (located in chromosome 16 and responsible for 90% of cases) and the second gene is called APKD2 (located on chromosome 2 and responsible for 10% of cases).
This disease has an autosomal dominant inheritance pattern. Usually, kidney problems will be present in older family members. Since in most cases kidney problems only appear at an older age, the absence of kidney problems does not rule out carrying the relevant mutations. For this reason, when one family member is diagnosed with ADPKD, screening other family members for this condition is also recommended.
Since each family has a unique mutation, genetic testing for this condition is considered complicated. However, more simple testing that does not include full sequencing of the relevant genes is possible, these tests screen for genetic patterns unique to the family.
What are the symptoms of ARPKD?
ARPKD is the more sever form of this disease. People with ARPKD suffer from kidney failure earlier in life. In some patients, kidney failure occurs prenatally, during pregnancy. These cases include low levels of amniotic fluid, leading to delay in lung development and early death. In less severe cases, kidney failure occurs neonatally, several months or even years after birth.
When kidney failure occurs at a very early age, treatment can prove difficult. In addition, this condition has significant effect on growth and general health. When cysts in the kidneys are present during pregnancy, this may indicate a severe form of the disease.
How is ARPKD inherited?
This disease is caused by a mutation in the gene ARPKD, located on the short arm of chromosome 1. The disease has an autosomal recessive inheritance pattern. Genetic testing for this mutation is often expensive and is not routinely preformed.
Parents with a child with ARPKD can test subsequent pregnancies for this disease through amniocentesis or chorionic villus sampling during weeks 10-12 of gestation.