Birt–Hogg–Dubé syndrome: A rare inherited autosomal dominant
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Birt–Hogg–Dubé syndrome (BHD) is a rare inherited autosomal dominant disorder caused by germline mutations in the tumor suppressor gene FLCN, encoding the protein folliculin. Its clinical expression typically includes multiple pulmonary cysts, recurrent spontaneous pneumothoraces, cutaneous fibrofolliculomas, and renal tumors of various histological types. BHD has no sex predilection and tends to manifest in the third or fourth decade of life. Multiple bilateral pulmonary cysts are found on chest computed tomography in >80% of patients and more than half experience one or more episodes of pneumothorax. A family history of pneumothorax is an important clue, which suggests the diagnosis of BHD.

Unlike other cystic lung diseases such as lymphangioleiomyomatosis and pulmonary Langerhans cell histiocytosis, BHD does not lead to progressive loss of lung function and chronic respiratory insufficiency. Renal tumors affect about 30% of patients during their lifetime and can be multiple and recurrent. The diagnosis of BHD is based on a combination of genetic, clinical, and/or skin histopathological criteria. Skin lesions of BHD do not need therapy, as there is no risk of malignant transformation. For aesthetic reasons, however, excision, debulking, ablative laser treatment (CO2 or Erb-Yag laser) or electrodessication can be proposed. However, recurrence may occur. One study failed to demonstrate significant cosmetic improvement with topical sirolimus, in contrast to its effect on angiofibromas in TSC.

In conclusion, As one of the three main causes of cystic lung diseases found at HRCT and present in up to 10% of patients with apparently spontaneous pneumothorax, BHD is now for the respiratory physician an important diagnosis to consider. When BHD is suspected, a multidisciplinary approach involving respiratory physicians, radiologists, geneticists, nephrologists, dermatologists, thoracic surgeons and pathologists is needed to confirm the diagnosis and to implement the appropriate follow-up, especially periodic kidney imaging for early detection of renal cancer. When BHD has been identified in an index patient, a diagnostic work-up of family members is another important step in the management of this genetic disorder with dominant autosomal transmission.

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