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PubMed This is a summary of 17 peer-reviewed journal articles Updated
Pulmonology

The Biology of Lung Collapse: Genes and Structures

At a Glance

Repeated familial lung collapses (FSP) are usually driven by genetic mutations, most commonly the FLCN gene linked to Birt-Hogg-Dubé (BHD) syndrome. This mutation weakens lung tissue, causing thin-walled cysts to form at the bottom of the lungs that can easily rupture and deflate the lung.

When a lung collapses repeatedly in a family, it is rarely due to simple “bad luck.” Instead, it often stems from specific biological “glitches” in how the lung is built and maintained. Understanding these differences can help you move from feeling like your body is unpredictable to understanding the structural reality of your condition.

The FLCN Gene: The “Anchorman” of Lung Cells

The most common biological driver of Familial Spontaneous Pneumothorax (FSP) is a mutation in the FLCN gene, which causes Birt-Hogg-Dubé (BHD) syndrome [1][2].

Think of the FLCN protein as a master regulator or “anchorman” for your lung cells. It helps cells stick together and respond to physical stress [3][4]. When this gene is mutated, several things happen:

  • Cell-to-Cell Adhesion: Cells don’t “grip” each other as tightly as they should [3].
  • The Stretch Hypothesis: Because the cells are less stable, the physical stress of breathing causes the tiny air sacs (alveoli) to gradually stretch out and enlarge [3][4].
  • mTOR Signaling: The loss of FLCN disrupts a major growth pathway called mTOR [5]. This disruption can cause cells to grow or behave abnormally, leading to the formation of thin-walled pockets [5][6].

Blebs, Bullae, and Cysts: What’s the Difference?

Doctors use specific terms to describe the “holes” or “pockets” in the lung. While they all look like air bubbles on a scan, they are biologically different:

Feature Blebs Bullae Cysts
Description Tiny blisters (under 1cm) on the lung surface [7]. Larger air pockets (over 1cm) within the lung tissue [8]. Thin-walled, rounded “balloons” within the lung tissue [9].
Location Usually at the very top (apex) of the lung [7]. Can be anywhere; often linked to smoking or emphysema [8]. In BHD, these are often at the bottom and outer edges of the lungs [10].
Context Seen in “typical” tall, thin young men (Primary Spontaneous Pneumothorax) [11]. Seen in chronic lung diseases like COPD [12]. The hallmark sign of BHD syndrome and other genetic conditions [2].

Why the Lung Collapses

A lung collapse happens when one of these air pockets ruptures. In BHD-related FSP, the cysts are often very thin-walled. Because they are integrated into the lung tissue rather than just sitting on the surface like a bleb, their rupture can create a significant leak that causes the lung to deflate like a punctured balloon [13][14].

Other Genetic Contributors

While BHD is the most frequent cause of familial collapses, genetic testing can easily rule out other rare genetic conditions that can weaken the “scaffolding” of the lung:

  • Marfan Syndrome (FBN1 gene): Affects the connective tissue throughout the body; people are often very tall with long limbs [15].
  • Vascular Ehlers-Danlos Syndrome (COL3A1 gene): A connective tissue disorder affecting blood vessels and organs. Genetic testing provides clarity so you aren’t left worrying about these vascular risks [16].
  • Alpha-1 Antitrypsin Deficiency: A protein imbalance that primarily causes early-onset emphysema, where bullae (large air pockets) develop as a secondary complication [17].

Identifying which biological “path” you are on is essential, as a BHD-related cyst requires a different monitoring strategy than a “typical” bleb [1][15].

Return to Home | Next: Decoding Your Diagnosis

Common questions in this guide

What is the difference between lung blebs and cysts?
Lung blebs are tiny blisters usually found on the top of the lung, often seen in typical spontaneous pneumothorax. Cysts, on the other hand, are thin-walled balloon-like pockets within the lung tissue itself, usually at the bottom of the lung, and are a hallmark of genetic conditions like BHD syndrome.
How does the FLCN gene mutation cause a lung collapse?
The FLCN gene helps lung cells stick together and respond to stress. When this gene is mutated, lung cells become less stable and form thin-walled cysts. If one of these fragile cysts ruptures, it creates an air leak that deflates the lung.
Besides BHD syndrome, what other genetic conditions can cause repeated lung collapses?
While BHD is the most common cause of familial lung collapses, genetic testing can rule out other conditions that weaken the body's connective tissue. These include Marfan Syndrome, Vascular Ehlers-Danlos Syndrome, and Alpha-1 Antitrypsin Deficiency.

Questions to Ask Your Doctor

Curated prompts to bring to your next appointment.

  1. 1.In my imaging, are the air pockets located at the top (apex) or the bottom (base) of my lungs, and does this favor a diagnosis of BHD?
  2. 2.Do you see evidence of blebs, bullae, or cysts, and could you explain which of these is most prominent in my case?
  3. 3.Given my family history, should we screen for connective tissue disorders like Marfan or Ehlers-Danlos in addition to BHD?
  4. 4.Is the mTOR signaling pathway involved in my condition, and are there any implications for future treatments?
  5. 5.How does the 'stretch hypothesis' apply to my lung health and risk of collapse during exercise or travel?

Questions For You

Tap a prompt to share your answer — we'll use it plus this page's context to start a tailored conversation.

References

References (17)
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    Familial spontaneous pneumothorax: importance of screening for Birt-Hogg-Dubé syndrome.

    Liu Y, Xing H, Huang Y, et al.

    European journal of cardio-thoracic surgery : official journal of the European Association for Cardio-thoracic Surgery 2020; (57(1)):39-45 doi:10.1093/ejcts/ezz171.

    PMID: 31177286
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    The Relevance of Family History Taking in the Detection and Management of Birt-Hogg-Dubé Syndrome.

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    Respiration; international review of thoracic diseases 2019; (98(2)):125-132 doi:10.1159/000498973.

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    Mechanisms of pulmonary cyst pathogenesis in Birt-Hogg-Dube syndrome: The stretch hypothesis.

    Kennedy JC, Khabibullin D, Henske EP

    Seminars in cell & developmental biology 2016; (52()):47-52.

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    New Developments in the Pathogenesis of Pulmonary Cysts in Birt-Hogg-Dubé Syndrome.

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    Birt-Hogg-Dubé syndrome: Another mTOR phenomenon.

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    PMID: 35907578
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    Clinic Examination and Gene Diagnosis for a Birt-Hogg-Dubé Syndrome Family With a Novel flcn Frameshift Mutation Causing Nonsense-Mediated mRNA Degradation.

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    Human mutation 2025; (2025()):7194418 doi:10.1155/humu/7194418.

    PMID: 40677928
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    Expert consensus on spontaneous ventilation video-assisted thoracoscopic surgery in primary spontaneous pneumothorax (Guangzhou).

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    Annals of translational medicine 2019; (7(20)):518 doi:10.21037/atm.2019.10.08.

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    A Systematic Review of the Respiratory Effects of Inhalational Marijuana.

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    Chest Computed Tomographic Image Screening for Cystic Lung Diseases in Patients with Spontaneous Pneumothorax Is Cost Effective.

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    Birt-Hogg-Dubé syndrome: a large single family cohort.

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    Spontaneous Pneumothorax Secondary to Bullous Lung Emphysema Positive for Cannabinoids upon Toxicological Examination.

    Bisconti M, De Palma A, Pacifici R, et al.

    Journal of clinical medicine 2023; (12(15)) doi:10.3390/jcm12154956.

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    Correlative analysis of lung CT findings in patients with Birt-Hogg-Dubé Syndrome and the occurrence of spontaneous pneumothorax: a preliminary study.

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    A Rare Case of Spontaneous Pneumothorax Recurrence 30 Years After Surgery in a Patient with Birt-Hogg-Dube Syndrome: Case Presentation and Short Review of the Literature.

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    The Mystery of Ehlers-Danlos Syndrome: An Autobiographical Case Report.

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This page explains the genetics and biology of familial spontaneous pneumothorax for educational purposes only. Always consult your pulmonologist or genetic counselor for an accurate diagnosis and personalized medical advice.

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