Introduction

Did you know that some rare and painful skin ulcers may not result from injury or infection, but from an overactive immune system that mistakenly targets the body's own tissues? One such condition is pyoderma gangrenosum (PG), a complex and uncommon skin disease that can have a profound impact on daily life. It typically presents as rapidly developing ulcers, most commonly on the legs, but it can affect other parts of the body as well. The ulcers are often deep, with purple or blue-coloured borders, and can worsen very quickly without appropriate treatment.

In many individuals, PG is linked to other chronic health conditions such as inflammatory bowel disease, arthritis, or blood disorders. More recently, researchers have begun uncovering genetic factors and familial patterns that may influence who develops PG and how severe it becomes. These discoveries offer hope for early diagnosis, targeted treatment, and improved quality of life.

This article aims to explain the role of genetics in PG, highlight key hereditary syndromes associated with it, and make sense of the scientific literature for those concerned about inherited risk. Whether you or a loved one has been affected, understanding the genetic basis may offer clarity and open doors to better care.

Genetic factors of PG

There is growing evidence that genetic factors contribute to the development of pyoderma gangrenosum, particularly in familial cases. PG has been associated with autoinflammatory syndromes and mutations in genes regulating immune responses.

Key findings:

• PG can occur as part of hereditary syndromes such as PAPA (pyogenic arthritis, PG, and acne), PASH (PG, acne, and suppurative hidradenitis), and PAPASH (pyogenic arthritis, PG, acne, and suppurative hidradenitis), all linked to immune system dysregulation¹
• Mutations in the PSTPIP1 gene, which affects inflammation regulation, have been identified in several patients with familial PG and syndromic variants like PAPA²
• Genetic studies in patients with PASH and PAPA syndromes have shown altered cytokine expression and shared pathways with other autoinflammatory diseases³
• PG has also been observed in families with MEFV mutations, which are better known for causing familial Mediterranean fever, suggesting shared inflammatory mechanisms⁴

These findings strongly support a hereditary component in select cases of PG. Understanding the genetic links in PG is vital for improving diagnosis and personalising treatment. Read on to explore how syndromic presentations, gene mutations, and cytokine pathways all come together in shaping this complex disease.

What is pyoderma gangrenosum?

Pyoderma gangrenosum is a type of neutrophilic dermatosis, meaning it involves an excessive build-up of neutrophils, a type of white blood cell, in the skin. These cells mistakenly attack the body’s own tissues, causing inflammation and ulceration. It typically presents as rapidly enlarging painful skin ulcers with raised and violaceous borders, often starting after a minor skin trauma or injury. This phenomenon is known as pathergy.

PG is most commonly found in adults aged between 20 and 50 and is more prevalent in females than males. Although its precise cause is unknown, around 50% of PG cases occur in association with underlying systemic diseases such as inflammatory bowel disease (IBD), rheumatoid arthritis, or haematological malignancies.⁵

However, in 10–20% of cases, no underlying illness is found. These idiopathic forms may involve genetic susceptibility or unrecognised autoinflammatory processes. Over the past two decades, the classification of PG has shifted from an autoimmune condition to a disorder with features of autoinflammation.

Genetic syndromes and pathways in PG

PAPA syndrome

PAPA syndrome is an autosomal dominant hereditary disorder. It is one of the clearest examples of a genetic cause for PG. The syndrome consists of three primary symptoms: pyogenic sterile arthritis, pyoderma gangrenosum, and severe cystic acne. It is linked to mutations in the PSTPIP1 gene, which encodes a protein involved in regulating the inflammasome complex. The inflammasome is essential for controlling inflammation.

Mutations in PSTPIP1 result in enhanced interaction with pyrin, a protein also involved in inflammation regulation. This leads to increased production of proinflammatory cytokines, particularly interleukin-1 beta (IL-1β), contributing to the inflammatory symptoms seen in PG.²

PASH and PAPASH syndromes

PASH and PAPASH are newly recognised syndromes in the spectrum of autoinflammatory diseases. While PASH includes PG, acne, and hidradenitis suppurativa, PAPASH also includes arthritis.

Unlike PAPA syndrome, PSTPIP1 mutations are not consistently found in PASH and PAPASH. However, studies show overexpression of IL-1β, IL-8, CXCL1, CXCL2, and CXCL3, and increased activity of CD40/CD40L systems, supporting an autoinflammatory basis.³ These cytokines promote neutrophil recruitment, inflammation, and tissue damage in skin lesions.

Four out of five patients in a PASH case series displayed mutations in genes known to be associated with other autoinflammatory diseases, despite the absence of a definitive genetic cause.³

MEFV and pyrin pathways

The MEFV gene encodes pyrin, a protein involved in innate immune responses; mutations in MEFV cause familial Mediterranean fever (FMF), another autoinflammatory condition. PG has been documented in patients with FMF, with MEFV mutations identified in these individuals.⁴ Since pyrin also interacts with PSTPIP1, this supports the hypothesis that PG can emerge through shared inflammatory pathways.

Familial patterns and inheritance

Familial PG is rare but documented. In a systematic review of PG cases, approximately 1.7% were found to occur in familial clusters.⁵ These cases typically present early on and may involve more severe or recurrent disease. A landmark case report described three generations of a family affected by PG and arthritis, leading to the identification of PAPA syndrome.⁶

These familial cases do not always meet criteria for syndromic diagnoses, suggesting that there may be undiscovered or less penetrant genetic variants contributing to susceptibility. Other studies have proposed that the inheritance pattern in familial PG may be autosomal dominant with genetic variability, or polygenic with environmental modifiers.

Genetic testing and diagnostic criteria

In patients with early-onset PG, associated arthritis or acne, or family history, genetic testing is increasingly recommended. Testing for PSTPIP1 mutations, MEFV, and other autoinflammatory genes may reveal underlying causes, especially in syndromic presentations.

In 2018, diagnostic criteria for PAPA-related syndromes were proposed, requiring clinical features of sterile arthritis, PG, and acne, supported by genetic findings. These criteria help standardise recognition and encourage appropriate testing.

Additionally, a Delphi consensus in 2018 proposed validated diagnostic criteria for PG, including major and minor elements such as rapidly progressive ulcers, exclusion of other causes, and histopathology showing neutrophilic infiltrates.

Implications for treatment

Recognising a genetic basis for PG shifts treatment strategies. Biologic therapies targeting inflammatory cytokines are proving effective in syndromic and familial PG:

• IL-1 inhibitors (e.g. anakinra) have yielded positive results in treating PAPA and PAPASH syndrome⁶
• TNF-α inhibitors (e.g. adalimumab) are effective for PG associated with hidradenitis suppurativa or arthritis³
• Combination therapies, including corticosteroids, colchicine, and cyclosporine, are used where biologics are unavailable or unaffordable⁷

By targeting the cytokine pathways involved, these treatments offer more durable remission with fewer side effects compared to broad immunosuppressants.

FAQs

Is pyoderma gangrenosum hereditary?

In most cases, PG is not hereditary. However, in a small subset of patients, especially those with associated conditions like arthritis and cystic acne, a genetic component may be involved.

What are the genetic syndromes associated with PG?

PAPA, PASH, and PAPASH syndromes are genetic or autoinflammatory syndromes where PG is one of the key clinical features. These syndromes involve genes like PSTPIP1 and MEFV.

Can genetic testing help diagnose PG?

Genetic testing is helpful in syndromic or familial cases of PG. It can identify mutations that explain the disease and help guide treatment.

What treatments are available for genetically linked PG?

Genetic testing is helpful in syndromic or familial cases of PG. It can identify mutations that explain the disease and help guide treatment.

Can children inherit PG from their parents?

In rare cases, yes. Familial cases have been described with autosomal dominant inheritance, particularly in PAPA syndrome.

Summary

Pyoderma gangrenosum is increasingly recognised as more than just a skin condition. In a subset of patients, especially those with familial cases or associated symptoms like arthritis and acne, genetic factors play a central role. Syndromes like PAPA, PASH, and PAPASH illustrate how mutations in genes such as PSTPIP1 and MEFV contribute to excessive inflammatory signalling and tissue damage.

While familial PG remains rare, its study is revealing important inflammatory mechanisms that may apply even in non-familial cases. Genetic testing, when clinically indicated, can support diagnosis, guide therapy, and inform family counselling.

Understanding the genetic basis of PG leads us toward more accurate diagnosis, earlier interventions, and ultimately, personalised treatment strategies that improve outcomes and quality of life.