PKD2 is a renal disorder characterized by the presence of fluid-filled cysts on the kidney. This results in renal insufficiency, enlarged kidneys and recurrent urinary tract infections. Patients often suffer from high blood pressure, abdominal and back pain, headaches and blood in their urine. Some patients may also exhibit non-renal manifestations such as hepatic cysts, dextrocardia and subtle craniofacial defects. The autosomal dominant form of polycystic kidney disease affects 1 in 500-1000 individuals. It has a later onset, with symptoms appearing in adulthood, compared to the autosomal recessive form which affects children. PKD is a progressive disorder and about half of all affected individuals develop end-stage renal disease by 70 years of age. The condition does not appear to have an ethnic or gender bias.
Imaging studies such as ultrasounds and MRI analysis help diagnose the disorder. While there is currently no cure for the condition, supportive and symptomatic treatment is available. Patients benefit from a low sodium diet, diuretics to remove excess fluid and surgery to drain cysts. Drugs to reduce blood pressure and relieve pain are also administered, as well as antibiotics for urinary tract infections. In the case of renal failure, patients require dialysis or kidney transplants.
The disorder follows an autosomal dominant pattern of inheritance with incomplete penetrance. It is caused by heterozygous mutations in the PKD2 gene. This gene encodes a large-conductance nonselective calcium-permeable cation channel that is located in renal epithelial cells and is involved in calcium ion transport and calcium signaling. The protein is also found in primary cilia, where it functions in mechanosensation of fluid flow and in response, stimulates an increase in intracellular calcium. By carrying out its functions, the PKD2 protein is found to be involved in cell proliferation, tubule development and normal kidney functioning. More than 75 PKD2 gene mutations have been identified in affected patients, including transitions, insertions and deletions that result in a truncated non-functional PKD2 protein.
Monies et al. (2017) discussed the findings of 1000 diagnostic panels and exomes carried out at a next generation sequencing lab in Saudi Arabia. One patient, a 2-year-old male, presented with bilateral nephrolithiasis. He also reported a family history of this phenotype. Using a multigene panel for renal disorders, a heterozygous mutation (c.567G>A, p.W189X) was identified in exon 1 of the patient’s PKD2 gene, associated with polycystic kidney disease 2. The case highlighted the importance of molecular testing, as identification of the PKD2 variant led to a highly altered course of disease management. Also, given his unusually early presentation, the case helped in the phenotypic expansion of polycystic kidney disease.
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