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Polycystic kidney disease is characterised by cysts in the kidney which increase both in size and number, often resulting in kidney failure. There are several different types of the condition (an adult form and an infantile form), each with a different genetic basis, inheritance pattern and different clinical features. While the infantile form (ARPKD) is extremely rare, the adult form (ADPKD) is very common with variable age of onset. The two forms follow different patterns of inheritance in families: the adult form is inherited in an autosomal dominant manner while infantile form follows a pattern of autosomal recessive inheritance. ADPKD is known to be caused by faulty copies of at least three different genes. As a result, ADPKD has been classified into three subtypes: ADPKD-1, ADPKD-2, and ADPKD-3. The most common form of the condition, ADPKD-1, results from a faulty gene located on chromosome 16. ADPKD-2 is caused by changes in a gene on chromosome 4. These genes produce proteins known as ‘polycystin-1’ and ‘polycystin-2’ respectively. ARPKD is caused by changes in a gene located on the short ‘p’ arm of chromosome 6 (at 6p21.1-12). This gene produces a protein called fibrocystin. Despite the extreme variability in age of symptom onset and disease severity, there appears to be a single major faulty gene responsible for ARPKD. |