According to the author, knowledge of a disease-causing mutation in a single-gene disorder represents one of the strongest diagnostic examples of personalised medicine. This is because the mutation conveys an almost 100 percent risk of developing the disease by a defined age.

Mutation analysis reveals the primary cause of the disease because of the strong genotype-phenotype correlation of almost 100 percent that is noted in recessive single-gene renal disorders. It allows prenatal diagnostic tests to be done, and has a high diagnostic and prognostic value. Mutations convey an almost 100 percent risk of developing, for instance, autosomal recessive polycystic kidney disease.

Single-gene defect kidney diseases are grouped according to main diagnostic features.

• Glomerular diseases affect the kidney's filtering apparatus and include steroid-resistant nephrotic syndrome. It usually manifests as focal segmental glomerulosclerosis, a replacement of the filtering units by scar tissue. In children, this is associated with a 30 percent risk of recurrence in a kidney transplant. Facial swelling, low blood proteins, abnormal blood fats, and high blood pressure can all be symptoms.

• Renal cystic ciliopathies are kidney diseases involving cysts, rounded hollow spaces in the kidney. For example, autosomal dominant polycystic kidney disease (ADPKD) is the most frequent lethal heritable dominant disease in the USA and Europe. It affects about 1 in 1,000 people. Chronic kidney disease develops by age 60 to 70 years. 90 percent of ADPKD cases can now be diagnosed by mutation testing. This is helpful for clinical decision making, especially in living-related donor transplantation.

(Medical News Today)

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• Renal tubular disorders affect reuptake of water, salt, and sugars from the glomerular filtrate which is the fluid in the kidney post-filtration. In such disorders, the primary genetic defect causes loss of function of a specific renal transport protein or signalling molecule. For instance, sodium reabsorption abnormalities cause Bartter's syndrome leading to loss of salt from the kidneys.