What causes bhd

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Last updated: April 4, 2026

Quick Answer: BHD, or Birt-Hogg-Dubé syndrome, is a rare genetic disorder caused by mutations in the FLCN gene. These mutations lead to the development of non-cancerous tumors (hamartomas) in various organs, most notably the skin, lungs, and kidneys.

Key Facts

BHD is caused by mutations in the FLCN gene, which is responsible for producing the folliculin protein.
The primary symptoms include fibrofolliculomas (skin tumors), pulmonary cysts, and kidney tumors.
BHD is inherited in an autosomal dominant pattern, meaning only one copy of the mutated gene is needed to cause the condition.
Individuals with BHD have an increased risk of developing kidney cancer, although the lifetime risk is lower than initially thought.
Diagnosis is typically made through a combination of clinical examination, family history, and genetic testing.

Overview

Birt-Hogg-Dubé syndrome (BHD) is a rare genetic disorder characterized by a predisposition to developing benign tumors, known as hamartomas, in specific organs. Named after the three families who first described it, BHD affects the skin, lungs, and kidneys. The underlying cause of BHD is mutations in the FLCN gene, which plays a crucial role in cell growth and regulation. This genetic defect disrupts the normal function of the folliculin protein, leading to the abnormal proliferation of cells and the formation of tumors.

Genetics of BHD

BHD is inherited in an autosomal dominant pattern. This means that a person only needs to inherit one copy of the mutated FLCN gene from either parent to develop the condition. If one parent has BHD, each child has a 50% chance of inheriting the mutated gene and developing the syndrome. While the gene mutation is the direct cause, the specific symptoms and their severity can vary significantly among affected individuals, even within the same family. This variability is known as variable expressivity.

Clinical Manifestations

The hallmark features of BHD manifest in three primary organ systems:

Skin Lesions (Fibrofolliculomas)

The most common and often the earliest sign of BHD is the development of multiple, small, benign skin tumors called fibrofolliculomas. These typically appear on the face, neck, and upper chest, usually starting in early adulthood. They are often described as small, flesh-colored or slightly translucent bumps. While generally asymptomatic, they can be cosmetically concerning for affected individuals. Other skin lesions, such as trichodiscomas and acrochordons, may also be present.

Pulmonary Manifestations

Individuals with BHD are prone to developing spontaneous pneumothorax (collapsed lung) due to the presence of lung cysts. These cysts can vary in size and location within the lungs. Recurrent pneumothoraces can lead to significant respiratory issues and discomfort. The exact mechanism by which the FLCN gene mutation leads to cyst formation is still being researched, but it is believed to involve altered cell signaling pathways that affect lung tissue structure.

Kidney Tumors

A significant concern for individuals with BHD is the increased risk of developing kidney tumors. These tumors can be benign (oncocytomas, angiomyolipomas) or malignant (renal cell carcinoma). The type and behavior of kidney tumors in BHD can differ from those seen in the general population. While the risk of kidney cancer is elevated, studies suggest that the lifetime risk might be lower than previously estimated, and many kidney tumors in BHD are slow-growing. Regular screening and monitoring of the kidneys are therefore crucial for early detection and management.

Diagnosis of BHD

Diagnosing BHD typically involves a combination of factors:

Clinical Evaluation: A thorough physical examination looking for characteristic skin lesions and a review of symptoms such as pneumothorax or kidney issues.
Family History: A detailed family history is important, given the genetic nature of the condition.
Genetic Testing: Confirmation of BHD is usually achieved through genetic testing that identifies mutations in the FLCN gene.

Diagnostic criteria may vary slightly between different medical institutions, but generally include the presence of fibrofolliculomas in combination with a family history of BHD or a history of spontaneous pneumothorax or kidney tumors.

Management and Monitoring

There is currently no cure for BHD, as it is a genetic condition. Management focuses on monitoring for and treating the symptoms and associated risks:

Skin: Fibrofolliculomas are usually treated for cosmetic reasons or if they cause discomfort. Treatments can include surgical excision, laser ablation, or cryotherapy.
Lungs: Patients prone to pneumothorax require careful management, including counseling on activities that increase risk and, in some cases, surgical interventions to prevent recurrence.
Kidneys: Regular surveillance of the kidneys is essential. This typically involves periodic imaging studies (such as CT scans or ultrasounds) to detect any developing tumors. If tumors are found, treatment depends on their size, type, and location, and may involve surveillance, partial nephrectomy, or other surgical approaches.

Genetic counseling is also an important aspect of managing BHD, helping affected individuals and their families understand the inheritance pattern and implications of the condition.

Research and Future Directions

Ongoing research aims to better understand the precise functions of the folliculin protein and the mechanisms by which FLCN gene mutations lead to tumor formation. This research may lead to the development of targeted therapies or improved screening strategies in the future. Understanding the variability in disease presentation is also a key area of investigation.