Are Cysts Genetic? Inherited vs. Non-Genetic Causes

Some cysts are directly caused by inherited gene mutations, but the majority of cysts people develop over a lifetime have nothing to do with genetics. The word “cyst” describes a fluid-filled sac, and that basic structure can arise from dozens of different mechanisms: a blocked gland duct, an injury that traps skin cells beneath the surface, a parasite burrowing into liver tissue, or the slow wear of aging kidneys. The genetic forms tend to be the most medically serious, particularly polycystic kidney disease, but they represent a small fraction of all cyst diagnoses. Understanding which cysts trace to DNA and which do not changes how you think about family risk, screening, and treatment.

Cysts Caused by Single-Gene Mutations

The clearest example of a genetic cyst disease is autosomal dominant polycystic kidney disease (ADPKD), the most common inherited kidney disorder. It is caused by mutations in one of two genes, PKD1 or PKD2, which encode proteins called polycystins. These proteins help kidney tubule cells sense fluid flow and maintain their normal structure. When one copy of PKD1 or PKD2 is mutated from birth, cysts gradually develop in both kidneys over decades, eventually compromising kidney function. In genetic screening studies, PKD1 mutations account for roughly 87% of identified cases and PKD2 for the remaining 13%, with PKD1 mutations generally leading to more severe disease and earlier kidney failure.¹ Because ADPKD follows a dominant inheritance pattern, a child of an affected parent has a 50% chance of inheriting the condition.²

A rarer and more severe counterpart is autosomal recessive polycystic kidney disease (ARPKD), caused by mutations in the PKHD1 gene on chromosome 6. Because this form is recessive, a child must inherit a defective copy from both parents. The severity depends heavily on the type of mutations involved: children carrying two truncating mutations (which completely disable the protein) almost always die in the perinatal or neonatal period, while those who survive infancy typically carry at least one missense mutation that leaves the protein partially functional.³ The PKHD1 protein localizes to structures called primary cilia on kidney cells, and reduced levels of this protein appear to be central to cyst formation.⁴ Among children who survive, though, the specific PKHD1 mutation type does not reliably predict kidney size or function, making prognosis difficult even with genetic information in hand.⁵

The Two-Hit Mechanism Behind Inherited Cysts

One puzzle about ADPKD is that every cell in the kidney carries the same inherited mutation, yet cysts form only in scattered spots along the tubules. The explanation, supported by substantial evidence, is a “two-hit” model. A person with ADPKD inherits one mutated copy and one normal copy of PKD1 or PKD2. Most kidney cells get by on the normal copy alone. But over time, individual cells randomly sustain a second mutation that knocks out the remaining good copy. Once both copies are lost, that cell loses its ability to regulate growth properly and begins forming a cyst.

Researchers have confirmed this mechanism by isolating DNA from individual cysts. In liver cysts from ADPKD patients with PKD1 mutations, somatic inactivation of the normal PKD1 allele was detected in a large fraction of cysts, and in every case where the affected allele could be identified, it was the normal copy (inherited from the unaffected parent) that had been lost or mutated.⁶ The same pattern holds for PKD2 mutations. In one study of 54 kidney and liver cysts from patients with known PKD2 mutations, unique somatic mutations were found in twelve cysts, and in eleven of those twelve, the somatic hit had struck the copy inherited from the unaffected parent.⁷ Additional work examining 21 cysts from one ADPKD2 patient found that about a third harbored the same insertion mutation in the wild-type PKD2 allele.⁸

This two-hit process explains why ADPKD is slow and variable: cyst formation depends on random somatic mutations accumulating over years, which is why kidney function often holds up until middle age and why two siblings with the same inherited mutation can have very different disease courses.

Syndromic Conditions and Ciliopathies

Beyond ADPKD and ARPKD, cysts appear as part of broader genetic syndromes. Von Hippel-Lindau (VHL) syndrome, caused by mutations in the VHL tumor suppressor gene, predisposes people to cysts and tumors in multiple organs, particularly the kidneys. A case report described a 16-year-old diagnosed with VHL syndrome after ultrasound revealed multiple renal cysts, later confirmed by molecular testing showing deletion of the entire VHL gene.⁹ In VHL, the renal cysts themselves can sometimes progress to clear cell renal carcinoma, which is why surveillance is critical for affected families.

Many of these genetic cyst diseases share a common thread: they involve defects in primary cilia, the tiny hair-like sensory structures present on nearly every cell in the body. The proteins encoded by PKD1, PKD2, and PKHD1 all localize to or interact with primary cilia. This broader category of diseases, called ciliopathies, includes not just polycystic kidney disease but also conditions involving liver and pancreatic cysts, retinal degeneration, brain anomalies, skeletal abnormalities, and even obesity and diabetes.¹⁰ Mutations in ciliary genes affect renal cystic diseases specifically, including nephronophthisis and several rare syndromes such as Joubert, Meckel-Gruber, and Bardet-Biedl syndromes.¹¹ The unifying concept is that when cells cannot properly sense their environment through cilia, they lose the growth-regulation signals that prevent cyst formation.¹²

Cysts With a Complex Genetic Background

Not every cyst with a genetic component follows a clean single-gene inheritance pattern. Polycystic ovary syndrome (PCOS), a condition affecting roughly one in ten women of reproductive age, produces fluid-filled cysts on the ovaries. But PCOS does not trace to a single gene. It arises as a complex trait from the interaction of multiple genetic variants and environmental influences.¹³ Heritable factors include a tendency toward excess androgen production, insulin resistance, and particular ovarian morphology, but environmental triggers like diet and weight play a substantial role in whether the syndrome manifests clinically.

Genetic studies have identified variants in genes related to androgen production, insulin signaling, inflammation, and energy balance that may predispose someone to PCOS, but no single variant is sufficient to cause it.¹⁴ Gene expression studies show altered activity in pathways controlling steroid hormone production, gonadotropin regulation, insulin action, and chronic inflammation.¹⁵ This means PCOS runs in families to a degree, but having a mother or sister with the condition does not guarantee you will develop it. It also means the ovarian cysts in PCOS are biologically quite different from the renal cysts of ADPKD, even though both involve fluid-filled sacs and both have genetic underpinnings.

Common Cysts That Have Nothing to Do With Genetics

Most cysts that bring people to a doctor are not genetic at all. The everyday cysts you can feel under the skin, see on imaging by accident, or notice in a joint are overwhelmingly caused by mechanical or environmental factors.

• Epidermal cysts: The most common type of skin cyst. They form when hair follicle inflammation or a minor injury traps skin cells beneath the surface, where they continue producing keratin and form a growing sac.¹⁶ Surgery, piercings, and even splinters can trigger them.
• Ganglion cysts: Rubbery lumps that appear near wrist or hand joints. The exact mechanism is not fully settled, but the leading theory holds that small deposits of mucin-like material outside the joint coalesce into the main body of the cyst, with a wall and connecting stalk forming afterward.¹⁷ Repetitive joint stress may contribute, but no genetic cause has been identified.
• Bartholin’s cysts: Cysts of the Bartholin’s glands near the vaginal opening, caused by mucus building up when a gland duct becomes blocked.¹⁸ Infection or inflammation triggers the blockage, not an inherited gene.
• Hydatid cysts: Caused by the tapeworm Echinococcus granulosus, which forms large fluid-filled cysts primarily in the liver and lungs.¹⁹ These are entirely environmental, acquired by ingesting parasite eggs from contaminated food, water, or contact with infected animals.
• Branchial cysts: Neck cysts that form from embryonic tissue left behind during fetal development. Vestigial remnants from incomplete closure of the branchial apparatus can persist as buried cell rests that later form cysts.²⁰ These are congenital but not inherited in the way ADPKD is. They arise from random developmental events rather than from a mutation passed down through a family.

The distinction between congenital and inherited is worth emphasizing. Branchial cysts are present from birth (congenital), but they are not caused by a gene that a parent carries and could pass to multiple children. They are one-off developmental accidents. People sometimes assume “congenital” means “genetic,” but the two words describe different things.

Aging and Simple Kidney Cysts

If you are over 40 and get an abdominal scan for any reason, there is a reasonable chance the radiologist will mention a simple kidney cyst. These are extremely common and overwhelmingly benign. In one study using CT scans of patients without known kidney disease, no cysts were found in anyone under 40, but the number and size of cysts increased steadily with age after that point.²¹ Broader research on age-related kidney changes confirms that older age is associated with larger and more numerous kidney cysts as part of normal structural aging.²²

Simple cysts are not ADPKD, and finding one or two on a scan does not mean you have a genetic disease. The difference is that ADPKD produces many cysts in both kidneys, progressively enlarges the kidneys, and impairs function over time. A handful of simple cysts in someone over 50 is a normal finding. That said, the presence of cysts does correlate with slightly reduced kidney function even when they are considered “simple,” so they are not entirely trivial as a marker of kidney aging.²³

When Environment Modifies Genetic Disease

Even for the clearly genetic cyst diseases, the environment matters more than many people assume. ADPKD progression varies enormously between individuals who carry the same type of mutation, and growing evidence points to diet, hydration, and metabolic factors as significant modifiers. A review of environmental triggers in ADPKD argued against the “fatalistic view” of the disease as purely genetic, presenting evidence that excess carbohydrate intake, insulin resistance, dehydration, electrolyte imbalances, exposure to kidney-toxic substances, and gut microbiome disruption all accelerate cyst growth and kidney decline.²⁴ The highly variable rates of disease progression among ADPKD patients support the idea that nutritional and lifestyle factors significantly influence the disease course.²⁵

There are also cases where medications produce cysts in people with no genetic predisposition at all. Long-term lithium therapy, used for bipolar disorder, can cause severe cystic kidney disease that mimics the appearance of ADPKD on imaging, with multiple bilateral cysts and enlarged kidneys, in patients with no family history of inherited cyst disease.²⁶ This is a purely drug-induced effect, unrelated to PKD1 or PKD2 mutations. It illustrates why imaging alone cannot always distinguish genetic from non-genetic cyst disease and why clinical context matters enormously.

Genetic Testing and What It Changes

For kidney cysts in particular, genetic testing has moved from a research curiosity to a practical clinical tool. It is now readily available to distinguish between different genotypes and is increasingly used for both diagnostic and prognostic purposes.²⁷ Knowing whether a patient carries a PKD1 or PKD2 mutation, and which specific mutation they have, can inform predictions about disease trajectory and help guide treatment decisions.

This matters because treatment options now exist that are genotype-aware. Tolvaptan, a drug that blocks a specific kidney receptor, has been shown to slow kidney volume growth, preserve kidney function longer, and reduce pain in ADPKD patients whose kidneys are not yet severely damaged.²⁸ Research into how it works suggests it may also reduce inflammation-driven kidney injury by lowering the mechanical stress that cysts impose on surrounding tissue.²⁹ The drug is not appropriate for all patients, and selecting the right candidates involves weighing genetic test results, kidney volume, and rate of decline. None of that matters if you have a simple age-related cyst or a blocked Bartholin’s gland. The genetic question is medically relevant primarily when cysts are numerous, bilateral, or appearing in someone with a family history.

How Doctors Evaluate Cystic Kidney Lesions

When imaging reveals a kidney cyst, radiologists use a standardized framework called the Bosniak classification to assess whether it is likely benign or potentially cancerous. The system has been in use for over 30 years and stratifies cystic renal masses by features like wall thickness, internal septations, and enhancement patterns on CT scans.³⁰ A systematic review and meta-analysis confirmed that the classification accurately stratifies malignancy risk in cystic renal lesions.³¹

The Bosniak system does not tell you whether a cyst is genetic. A Bosniak I cyst (a thin-walled, water-density cyst with no enhancement) is almost certainly benign regardless of whether the patient has ADPKD or age-related cysts. What the system does is separate the cysts that need surgery or close monitoring from the ones that can be safely ignored. For anyone anxious about a cyst found on a scan, the Bosniak category is usually more immediately relevant than the genetic question.

Polycystic Kidney Disease in Other Animals

ADPKD is not unique to humans. Persian cats and related breeds carry their own version of polycystic kidney disease, caused by mutations in the feline PKD1 gene that closely parallel the human form. The disease in cats shows similar genetics, presentation, and progression to the human version, and because cats have longer lifespans and larger kidneys than rodent models, they serve as an efficient large-animal model for testing new ADPKD treatments.³² Responsible breeders now screen for the mutation, and genetic testing in Persian cats has become routine in many countries. The conservation of this disease across species underscores just how fundamental the polycystin pathway is to normal kidney development, and how far back in evolutionary history the vulnerability to cyst formation goes.