Familial Juvenile Hyperuricaemic Nephropathy
What else is it called?
- medullary cystic kidney disease
- renin associated kidney disease
- uromodulin associated kidney disease
- medullary cystic kidney disease type 1
- medullary cystic kidney disease type 2
- Autosomal dominant tubule-interstitial kidney disease
- Autosomal dominant medullary cystic kidney disease type 2 (former)
- UMOD-related ADTKD
- Autosomal dominant medullary cystic kidney disease type 2
- UMOD-related autosomal dominant tubulointerstitial kidney disease
- Familial juvenile hyperuricemic nephropathy type 1
- Familial Juvenile Hyperuricemic Nephropathy 1
- UMOD-Associated Kidney Disease
- Uromodulin kidney disease
- ADTKD due to UMOD mutations
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What causes it?
There are three subdivisions (types) of this condition; ADTKD-UMOD, ADTKD-REN and ADTKD-MUC1.
ADTKD-UMOD (also known as uromodulin kidney disease) is caused by a mutation (change) in a gene that encodes (converts) the protein called uromodulin. This abnormal protein builds up in the kidney cells and causes slow progression of kidney disease. The reason why patients with this disorder develop gout (a form of arthritis) is still unclear.
ADTKD-REN is caused by a mutation (change) in a gene that encodes (converts) the protein called renin. The protein either builds up in the kidney cells or is not produced in large enough amounts when needed. This leads to slow progression of kidney disease. Patients have low amounts of renin which may cause mildly low blood pressure and mildly high potassium levels.
ADTKD-MUC1 is caused by a mutation (change) in the gene that encodes (converts) mucoprotein-1. This is a protein that is made in many of the cells of the body to provide a protective lining in the stomach, lungs, kidney tubules and many other areas. However, the mutation only leads to complications in the kidney with no problems in the other organs and tissues.
ADTKD of unknown genetic cause is caused by a mutation (change) in a gene but the gene that causes this condition is still unknown.
How common is it?
All forms of autosomal dominant tubulointerstitial kidney disease are very uncommon. The exact prevalence of this condition is unknown.
What are the signs and symptoms?
All individuals with ADTKD show slow loss of kidney function that may happen as early as childhood. The first sign that usually leads to a diagnosis is elevated blood creatinine levels (measure of kidney function) found through a routine blood test at the doctor’s office.
Other signs and symptoms of the condition include:
- Gout (a form of arthritis/joint inflammation)
- Hyperuricemia (high blood uric acid levels)
- Nephritis (kidney inflammation)
- Nausea and fluid retention (symptoms of kidney failure)
- Renal insufficiency (renal failure/kidney failure)
- Anaemia (lacking healthy red blood cells to carry around oxygen, causing fatigue)
Patients with ADTKD-MUC1 only have symptoms of chronic kidney disease, with no other symptoms present which makes this type even more difficult to diagnose.
Patients with ADTKD-UMOD also have elevated levels of blood uric acid that may lead to gout (a form of arthritis/joint inflammation).
Patients with ADTKD-REN all suffer from anaemia early in life, as early as 1 year of age. Anaemi usually improves during adolescence but normally returns when kidney failure becomes worse (usually around the age of 30-40). Patients also usually have low blood pressures and high blood potassium levels. In some patients with this condition, a more than normal amount of urine is produced which can cause bed-wetting in childhood.
Patients with ADTKD of unknown genetic cause, similarly to patients with ADTKD-MUC1 show only one symptom; slowly progressive kidney disease.
How is it diagnosed?
A number of specialised tests can be useful in diagnosing this condition. Specialised blood tests can be done to measure the blood creatinine levels and blood uric acid levels. Specialised urine tests are also carried out. The absence of blood or protein in the urine rules out other causes of kidney damage. A kidney biopsy may also be performed however, this cannot specifically diagnose ADTKD, genetic testing is required for that.
Molecular genetic testing is available for ADKTD-MUC1, ADTKD-UMOD and ADTKD-REN to confirm the diagnosis.
If no mutations are found, the patients have ADKTD of unknown genetic cause. Further genetic testing can be done to help diagnose this condition.
Can it be treated?
Treatment for this condition is focused on treating specific symptoms. Many patients with ADTKD-UMOD and ADTKD-REN suffer from gout. Gout is easily treated with medication (allopurinol). This medication should be stopped immediately in case of pregnancy or when becoming pregnant is possible.
In patients with ADTKD-REN, certain medication (fludrocortisone) may be effective in treating mildly high blood potassium and mildly low blood pressures. It is very important that individuals with ADTKD-REN are NOT put on a low sodium diet because this can worsen kidney function.
Anaemia in children with ADTKD-REN can be treated with a medication called erythropoietin.
There are no specific treatments for patients with ADTKD-MUC1 or ADTKD of unknown genetic cause.
Individuals with renin mutations should avoid non-steroidal anti-inflammatory medication such as ibuprofen or Naprosyn.
Do my family need to be tested?
Familial Juvenile Hyperuriceamic Nephropathy is an inherited condition. Humans have chromosomes made up of DNA. Genes are pieces of DNA that carry the genetic information. Each chromosome may have several thousand genes. We inherit chromosomes from the egg of the mother and sperm of the father. The genes on those chromosomes carry the instructions that determine a person’s characteristics, which are a combination of the parents.
The pattern of inheritance of Familial Juvenile Hyperuriceamic Nephropathy is autosomal dominant. This means that one copy of the altered gene in each cell is enough to cause the disorder. Cases can occur in people with no known family history of the disorder as it can result from a new mutation in the gene. Spontaneous mutations happen during the formation of an egg or sperm cell or during the development of the embryo.
A person affected by an autosomal dominant disorder such as Familial Juvenile Hyperuriceamic Nephropathy has a 50% chance of passing the mutated gene to each child. There is also a 50% chance that the child will not inherit the mutated gene.
Genetic counselling can be requested to get a full explanation. #