Alport syndrome is a genetic condition that primarily affects the kidneys but can also impact hearing and vision. Caused by mutations in genes that produce a vital protein in the body, this inherited disorder requires lifelong monitoring and care, though early treatment may help slow its progression.
Understanding Alport Syndrome
Alport syndrome is a rare inherited kidney disease that affects approximately 1 in 50,000 newborns. This condition is named after British physician Dr. A. Cecil Alport, who first described it in 1927 when he observed three generations of a family experiencing progressive kidney disease and hearing loss. He noted that blood in the urine was the most common symptom and that males were affected more severely than females.[1][4]
The disease occurs when the body fails to produce normal type IV collagen, which is a structural protein that acts like a scaffolding in various parts of the body. This protein is particularly important in the kidneys, ears, and eyes. Think of type IV collagen as three separate chains that need to twist together like a rope to function properly. These chains are called alpha 3, alpha 4, and alpha 5. When one of these chains is missing or defective, the rope cannot form correctly, leading to the symptoms of Alport syndrome.[1]
Prevalence estimates suggest there are fewer than 200,000 people in the United States living with Alport syndrome, making it officially classified as a rare disease. However, experts believe the condition is often underdiagnosed, meaning many people may have it without knowing. In one study examining chronic kidney disease of unknown cause, type IV collagen gene mutations accounted for the majority of hereditary kidney disease cases, suggesting that Alport syndrome may be more common than previously thought.[2][10]
What Causes Alport Syndrome
Alport syndrome is caused by genetic mutations in the genes responsible for producing type IV collagen. Specifically, mutations occur in three genes: COL4A3, COL4A4, and COL4A5. These genes provide instructions for making the components of type IV collagen that are essential for proper kidney function, hearing, and vision.[4]
In the kidneys, type IV collagen is a major part of the glomerular basement membrane (GBM), which is a critical structure that filters blood. The GBM is part of a three-layer system that removes toxins and waste from the blood to make urine, while keeping important substances like blood cells and proteins in the bloodstream. When the GBM doesn’t work properly due to abnormal collagen, blood and proteins leak into the urine, and the kidneys’ filtering ability gradually worsens over time.[1]
Because type IV collagen is also present in the inner ear and eyes, mutations in these genes can affect hearing and vision as well. The organ of Corti in the inner ear, which transforms sound waves into nerve impulses for the brain, relies on normal collagen structure. When this structure is abnormal, it can lead to progressive hearing loss. Similarly, collagen abnormalities in the eye can cause changes to the lens shape and retina coloring, though these changes rarely threaten vision.[4]
How Alport Syndrome Is Inherited
Alport syndrome can be inherited in three different patterns, each affecting individuals differently. Understanding the inheritance pattern is important because it influences disease severity and helps families understand their risk of passing the condition to their children.[1]
X-linked Alport syndrome (XLAS) is the most common form, accounting for approximately 60 to 80 percent of all cases. This type is caused by mutations in the COL4A5 gene, which is located on the X chromosome. Males have one X chromosome and one Y chromosome, while females have two X chromosomes. Because males have only one X chromosome, if they inherit the abnormal X chromosome, they typically develop more severe symptoms. Females who inherit one abnormal X chromosome usually have milder symptoms because their other X chromosome may partially compensate for the defective one.[1][4]
The inheritance pattern for XLAS follows specific rules. Males cannot pass the condition to their sons because they pass their Y chromosome to male children. However, all of their daughters will inherit Alport syndrome because males pass their X chromosome to all female children. Females with XLAS have a 50 percent chance of passing the condition to any of their children, regardless of the child’s sex.[1]
Autosomal recessive Alport syndrome (ARAS) accounts for approximately 15 percent of cases and is caused by mutations in the COL4A3 or COL4A4 genes located on chromosome 2. In this pattern, both parents must carry a mutation in the same gene for their child to develop the condition. Parents who are carriers typically don’t show symptoms, which is why they often don’t know they carry the mutation. When both parents are carriers, there is a 25 percent chance with each pregnancy that their child will inherit both mutated genes and develop Alport syndrome. Some carriers may develop a milder condition called thin basement membrane nephropathy, which mainly causes blood in the urine.[1][4]
Autosomal dominant Alport syndrome (ADAS) occurs in approximately 20 to 30 percent of cases. In this form, only one mutated copy of the COL4A3 or COL4A4 gene is sufficient to cause the disease. People with this form have a 50 percent chance of passing the condition to each of their children. Research suggests that autosomal dominant inheritance may actually be the most common form, though understanding of this pattern is still evolving.[4][14]
Risk Factors
The primary risk factor for developing Alport syndrome is having a family history of the condition. If anyone in your family has been diagnosed with Alport syndrome, progressive kidney disease, unexplained hearing loss starting in childhood or young adulthood, or a combination of these symptoms, other family members should be evaluated.[12]
Males with X-linked Alport syndrome face higher risks of developing severe symptoms compared to females with the same condition. Approximately 80 percent of males with XLAS develop hearing loss by their teenage years, and they are more likely to progress to end-stage kidney disease (ESKD), which is complete kidney failure requiring dialysis or transplant.[6]
The natural course and outlook for people with Alport syndrome varies considerably and is determined by both genetic factors and environmental influences. While having a particular genetic mutation sets the foundation for the disease, lifestyle factors and the timing of treatment interventions can significantly impact disease progression. Some genetic variants cause milder disease that progresses slowly, while others lead to rapid decline in kidney function.[10]
Symptoms of Alport Syndrome
The symptoms of Alport syndrome vary widely among individuals and depend on which genes are affected, the inheritance pattern, and the person’s age. The descriptions that follow refer to “classic” Alport syndrome, which typically causes significant disease starting in late childhood or young adulthood. Some individuals with milder mutations or carrier status develop disease later in life or show only some features of the classic disease.[5]
Kidney-Related Symptoms
Blood in the urine, called hematuria, is the hallmark symptom of Alport syndrome and is present from early infancy in nearly all affected individuals. Usually this blood can only be detected with a microscope or urine test strip, not with the naked eye. Sometimes young children with Alport syndrome have brown, pink, or red urine (visible blood in urine) for several days when they have an infection. This visible blood stops when the child recovers from the infection and, while alarming to see, is not harmful.[2][4]
As the disease progresses, additional signs of kidney disease appear. Protein begins to appear in the urine, a condition called proteinuria. This happens because the damaged kidney filters allow protein molecules that should stay in the blood to leak into the urine. The appearance of protein in the urine is now considered an important signal to begin treatment.[5]
High blood pressure, also called hypertension, commonly develops as kidney function declines. Blood pressure rises because the damaged kidneys cannot properly regulate fluid and salt balance in the body. Over time, the kidneys’ ability to filter waste products from the blood gradually decreases, reflected in blood tests that show rising levels of waste products like creatinine. This progressive loss of kidney function can eventually lead to end-stage kidney disease, where the kidneys can no longer sustain life without dialysis or kidney transplant.[4][5]
As kidney function declines, people may experience additional symptoms including swelling (particularly in the legs and feet), flu-like symptoms, fatigue, decreased appetite, and changes in urination patterns. These symptoms reflect the kidneys’ inability to remove excess fluid and waste from the body effectively.[1]
Hearing Loss
Many people with Alport syndrome develop progressive hearing loss, though some patients are not affected at all. Hearing is normal at birth in people with Alport syndrome. Hearing loss typically develops in late childhood or early adolescence, often when kidney function is still normal but substantial protein is present in the urine. In some patients, hearing loss is only noticed after kidney function has been lost.[4][5]
The hearing loss in Alport syndrome is sensorineural, meaning it’s caused by abnormalities in the inner ear rather than the outer or middle ear. Initially, people have difficulty hearing high-frequency sounds, but as time passes, the hearing loss becomes more severe and affects lower frequencies as well. Hearing loss in Alport syndrome is usually not complete, and good communication is almost always possible with the use of hearing aids.[5]
Eye Changes
Various eye abnormalities are often seen in people with Alport syndrome, though these rarely threaten vision or cause blindness. Affected individuals may have misshapen lenses in their eyes, a condition called anterior lenticonus, where the lens develops a cone-like shape. This can be treated by lens replacement surgery, similar to cataract surgery, if it affects vision.[4][5]
Abnormal coloring of the retina, which is the light-sensitive tissue at the back of the eye, is another common finding. Doctors may observe white or yellowish flecks in the macula (central part of the retina) and mid-periphery during eye examinations. Other eye changes can include corneal erosion, cataracts, and keratoconus, but these conditions seldom lead to significant vision loss.[4][5]
Other Features
A small percentage of people with X-linked Alport syndrome experience leiomyomas, which are benign (non-cancerous) smooth muscle tumors that can be found in the esophagus, lungs, uterus, and other female reproductive organs. When Alport syndrome occurs together with diffuse leiomyomatosis, the combination is commonly referred to by the acronym ASDL.[2]
Prevention and Screening
Because Alport syndrome is a genetic condition, there is no way to prevent it from occurring in someone who inherits the mutated genes. However, families with a history of Alport syndrome can take steps to identify affected members early and begin treatment promptly, which can significantly slow disease progression.[12]
If you have a family history of Alport syndrome, it is important to ensure that all family members, particularly males in families with X-linked inheritance, have been tested. Early diagnosis allows for earlier intervention with medications that can protect kidney function. Studies show that starting treatment early, even before symptoms become severe, can delay the onset of kidney failure by many years.[7][12]
Regular monitoring is essential for people diagnosed with Alport syndrome, even if they feel well. This includes periodic check-ups with a kidney specialist (nephrologist) to monitor kidney function through blood and urine tests, blood pressure measurements, and assessments of overall health. Regular evaluations of hearing and eyes are also important to detect and address problems early.[7]
Genetic testing and counseling are valuable for families affected by Alport syndrome. Understanding the specific genetic mutation and inheritance pattern helps families make informed decisions about family planning and helps identify other family members who may be at risk. Some families choose to use genetic testing during pregnancy or consider reproductive options to prevent passing the condition to children.[2][7]
Maintaining a healthy lifestyle is particularly important for people with kidney disease. General advice about eating healthily and living healthily is especially relevant for patients with kidney disease because they face an increased risk of heart disease, possibly due to high blood pressure and other factors. While specific dietary restrictions are typically not necessary early in the disease, people with Alport syndrome should limit salt intake because damaged kidneys struggle to eliminate excess salt, which can raise blood pressure. Very high protein intake, particularly protein supplements used for bodybuilding, should be avoided as it can stress the kidneys. Regular moderate exercise is generally beneficial and safe for people with Alport syndrome.[16][18]
How the Body Is Affected: Understanding the Disease Process
To understand what goes wrong in Alport syndrome, it helps to know how healthy kidneys work. Your kidneys contain millions of tiny filtering units called glomeruli. Each glomerulus contains specialized blood vessels that filter your blood through a three-layer membrane system. The middle layer of this system is the glomerular basement membrane, which is made largely of type IV collagen.[1]
This basement membrane acts like a sophisticated sieve. It allows water and waste products to pass through into the urine while keeping essential substances like blood cells and most proteins in the bloodstream. When type IV collagen is normal, the basement membrane maintains its proper structure and function throughout life.[1]
In Alport syndrome, mutations in the COL4A3, COL4A4, or COL4A5 genes result in the production of abnormal type IV collagen. This defective collagen cannot form the proper structure in the glomerular basement membrane. Over time, the abnormal basement membrane becomes increasingly damaged and scarred.[4]
As the basement membrane deteriorates, it becomes leaky. Red blood cells begin to pass through into the urine, causing hematuria. Later, as damage worsens, protein molecules also start leaking through, causing proteinuria. The filtering blood vessels in the glomeruli gradually become scarred and stop working altogether. As more and more glomeruli are destroyed, the kidneys lose their ability to filter waste products from the blood effectively.[4]
The scarring process in the kidneys, called glomerulosclerosis, is progressive and irreversible. As kidney function declines, waste products accumulate in the blood, fluid balance becomes disrupted, and blood pressure rises. Eventually, if the disease progresses untreated, the kidneys can no longer sustain life, and the person develops end-stage kidney disease requiring dialysis or transplantation.[4]
In the inner ear, abnormal type IV collagen affects the organ of Corti and other structures responsible for hearing. The defective collagen impairs the normal function of these delicate structures, particularly affecting the ability to hear high-frequency sounds initially. Over time, more frequencies are affected as the damage progresses, leading to more significant hearing impairment.[4]
In the eyes, abnormal collagen affects the shape and structure of the lens and may cause changes in the retinal coloring. While these changes are visible during eye examinations, they typically don’t interfere significantly with vision, unlike the serious effects on the kidneys and ears.[4]
