Polycystic Kidney Disease (PKD) is a range of inherited conditions that cause renal (kidney) failure, injury to other organs and sometimes result in premature death in children and adults. PKD is ’primarily characterised by the development of multiple micro and macroscopic cysts – sacs filled with fluid – throughout both kidneys and often, the liver.
There are 2 major forms of Polycystic Kidney Disease:
- Autosomal Dominant PKD or ADPKD
- Autosomal Recessive PKD or ARPKD
Both types of PKD occur from abnormalities or mutations in single genes inside human cells. Genes contain DNA, the ‘building blocks’ of life which contain instructions for making the proteins that are necessary for human development. When there is a genetic mutation, the proteins don’t work properly or are sometimes missed. In PKD, the genetic mutations affect the kidneys primarily, but also affect the development of the liver and other organs.
The genes are packed into 23 pairs of 46 chromosomes. One of each pair is inherited from each parent, along with any mutations.
PKD disorders are called ‘Autosomal’ because the mutations occur in one or more of the 22 chromosomal sets that are ‘non-sex’. (The 23rd pair are the XY chromosomes that determine gender.) PKD occurs equally in men and women with no gender bias.
ADPKD is the world’s most common inherited kidney disease, in which fluid-filled cysts develop, multiply and grow in both kidneys. Other organs, such as the liver and brain, may be affected.
Between 1 in 400 and 1 in 1000 people worldwide – about 12.5 million – have ADPKD. Over half of those affected will have kidney failure by the time they are 60 years old. Many will experience regular pain, disabiity and anxiety throughout life
ADPKD is caused by mutations in the PKD1 and PKD2 genes. It has a dominant pattern of inheritance which means that you only need an abnormal gene from one parent to cause ADPKD, even though the matching gene from the other parent is normal. The abnormal gene dominates.
Typically, ADPKD is inherited from a parent, but approximately 5-8% of cases are de novo’ or spontaneous mutations at conception. If you have ADPKD, there is a 1 in 2 (50 percent) likelihood that any children you have will inherit the disease. Each child’s risk is independent of other children. Children who do not inherit the abnormal gene will not develop or pass on the disease.
ARPKD is a rare and severe disease which can result in early kidney and liver failure. It occurs in about one in every 20,000 live births.
Sadly, about one baby in three with ARPKD dies from breathing problems during the first four weeks after birth and some will die during pregnancy.
However, 8 to 9 in ten babies (80-90 per cent) who survive the first four weeks of life are still alive at five years old. Encouragingly, a good number of children now survive into adulthood and are able to live full and productive lives.
ARPKD is caused by a mutation in the gene PKHD1. It has a recessive pattern of inheritance which means that you have to inherit two copies of an abnormal gene, one from each parent to get ARPKD. If you inherit only one mutated gene, you will be a ‘carrier’ but not develop ARPKD. However, when two carriers with the same abnormal ARPKD gene conceive a child, there is a 1 in 4 (25%) likelihood of passing the abnormal copy to the child. ARPKD will then occur.