Alport syndrome is a heritable condition caused by mutations in the genes that encode for a structural protein called type 4 collagen. This leads to type 4 collagen not working as intended, and to serious disease symptoms that include kidney disease, eye abnormalities, and hearing loss.
There are different types of Alport syndrome depending on the genes that are mutated, with some types more prevalent than others.
What is X-linked Alport syndrome?
X-linked Alport syndrome (XLAS) is caused by a mutation in the COL4A5 gene located on the X chromosome, one of the two sex chromosomes. It is the most common form of Alport syndrome, accounting for around 80 percent of diagnosed cases.
XLAS is more likely to affect men than women, because men have only one X chromosome (the other is the Y chromosome) while women have two X chromosomes. If a woman inherits only one copy of a disease-causing gene, the healthy copy of the gene on the other X chromosome can compensate. Female XLAS patients with just one affected gene usually only have hematuria, or evidence of blood in the urine. Still, some do experience more severe disease, including kidney failure.
Symptoms and diagnosis of XLAS
Hearing loss is often the earliest symptom of XLAS, with evidence of problems usually starting in the teenage years. A teacher is often among the first to notice that a child is truly struggling to hear in or outside of class. Hearing tests can confirm the presence of hearing loss.
All patients with XLAS will have kidney symptoms, usually in the form of protein or blood in the urine. In girls and women, these symptoms can be quite mild. But men with XLAS usually develop end-stage kidney disease by age 50. A kidney biopsy can be used to diagnose Alport syndrome. Blood tests and urine tests can also confirm that the kidneys are not filtering waste sufficiently and can help to track the progression of the disease.
Some patients with XLAS will have eye abnormalities, some of which can cause vision problems. These can be diagnosed through vision tests.
The surest method of diagnosing XLAS is a genetic test looking for mutations in the COL4A5 gene.
Although there is currently no cure for Alport patients, available treatments can ease some disease symptoms and delay kidney damage. It is also recommended that patients eat a “renal healthy” diet — one that is low in sodium, phosphates, and potassium.
Available surgical procedures can treat some eye of the abnormalities that affect vision in XLAS patients.
Most of these patients are good candidates for hearing aids, but it is recommended that patients begin to learn sign language as soon as hearing loss is evident.
Patients with hearing loss can develop profound deafness by their 40s or 50s. Men with XLAS usually have kidney failure by the time they are 50, and as a shorter lifespan as a result. Women with XLAS may or may not develop kidney failure.
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