If you (or your child) keep getting unusually severe or persistent fungal infections. For example, recurring thrush, deep skin fungus, or even fungal meningitis. Doctors may suspect a rare immune problem such as CARD9 deficiency. We can walk you through what CARD9 deficiency is, how genetic testing confirms it, and what happens next so you can make informed decisions with your care team.¹ 

CARD9 deficiency is confirmed by finding disease-causing mutations in both copies of the CARD9 gene on a genetic test. Once identified, clinicians verify the result (often with a second sequencing method), consider testing close relatives, and start a personalised plan—typically including long-term antifungal therapy and monitoring to prevent relapses.¹,²,³ 

Read on

Below, we explain the condition: symptoms to watch for, why genetic testing matters, how testing works, what “confirmatory diagnosis” means, and current treatment approaches.

Introduction

CARD9 deficiency is a rare, inherited primary immunodeficiency in which the immune system struggles to recognise and clear fungi while otherwise handling everyday infections normally. It follows an autosomal recessive pattern: a person must inherit faulty versions of CARD9 from both parents to be affected.¹,⁵

What is CARD9 deficiency?

“CARD9” stands for caspase recruitment domain–containing protein 9. The CARD9 protein is an adaptor used by innate immune cells (like neutrophils and dendritic cells) to signal that a fungus has been detected, triggering antifungal defences. When CARD9 is missing or non-functional, those signals are blunted, so fungi that are usually mild or superficial can become deep and invasive.¹,⁵ 

Symptoms and risk factors

Typical infections include:

• Chronic mucocutaneous candidiasis (recurrent thrush, nail and skin Candida)¹,³
• Deep dermatophytosis (severe ringworm caused by Trichophyton spp. invading deeper tissues), sometimes with lymph-node spread²
• Central nervous system (CNS) candidiasis (meningitis or brain abscesses), often in otherwise healthy children or young adults³
• Less common: fungal infections of bone (osteomyelitis), eye (endophthalmitis), sinuses, or rare mould/black-yeast infections (e.g., Phialophora, Exophiala)¹,⁷

Who gets it? Anyone can, but it is very rare. Because it’s autosomal recessive, the risk is higher when both parents are carriers; consanguinity increases this chance. Certain founder mutations have been described (for example, in parts of East Asia), which can cluster cases within families or communities.¹,⁸

Why genetic testing matters

Symptoms alone can look like “just bad luck” fungal infections. But genetic testing provides a definitive answer—it confirms that the root cause is CARD9 pathway failure, which changes management (for example, instituting long-term antifungal prophylaxis and screening siblings). In people with unexplained invasive fungal disease, experts recommend testing CARD9 (and often other immune genes) early to avoid delays.¹,³

How genetic testing for CARD9 deficiency works

1. Sample – Usually a standard blood test
2. Sequencing – The lab sequences the CARD9 gene (or uses an inborn-errors-of-immunity panel/whole-exome sequencing) to look for pathogenic variants. A diagnosis requires two disease-causing variants (either the same variant on both copies—homozygous—or two different variants—compound heterozygous)¹,³
3. Confirmation – Many labs verify new findings with a second method (for example, Sanger sequencing) before reporting¹
4. Result discussion – Your clinician or genetic counsellor explains the result, inheritance, and implications for relatives, and plans next steps¹

Confirmatory diagnosis: what comes after testing?

• Label the diagnosis – A positive test confirms CARD9 deficiency; records are updated so all your clinicians know³
• Family testing – Because siblings have a 25% risk of being affected if both parents are carriers, clinicians often test brothers/sisters and may test parents to document carrier status. This supports reproductive counselling¹,³
• Baseline assessment – Your team (often infectious diseases and immunology) reviews prior infections and screens for silent foci (skin, sinuses, eyes, CNS) to set a baseline
• Prevention plan – Many patients start long-term antifungal prophylaxis (for example, fluconazole) after invasive Candida or in high-risk scenarios, plus education on early symptom recognition¹

Can CARD9 deficiency be treated?

There’s no gene-fixing cure yet, but outcomes improve with targeted measures:

• Prompt, adequate antifungal therapy. Severe infections (e.g., Candida meningitis) typically require prolonged courses (for example, amphotericin B/voriconazole induction followed by oral azoles) and careful follow-up to confirm clearance³
• Secondary (and sometimes primary) prophylaxis. Long-term oral fluconazole is frequently used after invasive Candida to prevent relapse; some centres also consider prophylaxis in asymptomatic affected siblings after a family diagnosis¹,³
• Adjunct immune therapy in select cases. Case reports show GM-CSF (and occasionally G-CSF) added to antifungals can help clear refractory CNS candidiasis, likely by boosting neutrophil-mediated responses⁴,⁹
• Surgery/local control. Drainage or excision (e.g., of abscesses or fungal masses) is sometimes needed alongside medicines³
• Transplant? Haematopoietic stem-cell transplantation (HSCT) has cured isolated cases but carries significant risk; its role remains uncertain and is reserved for exceptional, life-threatening disease unresponsive to optimal therapy³

Living with CARD9 deficiency. With early diagnosis, proactive antifungal strategies, and regular specialist follow-up, many people study, work, and live full lives—just with extra vigilance around fungal exposures (for example, avoiding heavy mould environments) and prompt evaluation of suspicious symptoms.¹

Summary

• CARD9 deficiency is a rare, autosomal-recessive immune disorder causing selective susceptibility to fungi¹,⁵
• It presents with recurrent/severe fungal infections (skin/nails, deep dermatophytosis, and CNS candidiasis are red flags)²,³
• Genetic testing that finds two pathogenic CARD9 variants confirms the diagnosis; this enables family testing and a prevention-focused plan¹,³
• Long-term antifungal therapy (and, in selected cases, adjunct GM-CSF) reduces relapses and improves outcomes; HSCT is experimental and rare¹⁴

FAQs

Is CARD9 deficiency only a childhood disease?

No. While many cases present in childhood/adolescence, adults can present later—sometimes with their first episode being CNS candidiasis or deep dermatophytosis.¹,³,⁶ 

Why place the citation number after the full stop?

That’s Klarity’s style for references—superscript numerals after punctuation—, and it keeps the reading flow clean while allowing precise sourcing.

Can family members be tested?

Yes. Because inheritance is autosomal recessive, siblings of an affected person should be offered testing; parents are usually healthy carriers. Founder variants mean some families/populations see clustering.¹,⁸