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

BACKGROUND: Birt-Hogg-Dubé syndrome (BHDS) is a rare autosomal-dominant inherited disorder characterized by inactivation of the gene Folliculin (FLCN), pulmonary cysts with recurrent spontaneous pneumothorax, dermatological lesions, and an increased risk of developing renal malignancies. OBJECTIVES: We aimed to investigate the real prevalence of BHDS and its prevalence among patients with a familial history of pneumothorax. METHODS: From July 2014 to December 2016, we consecutively studied all patients with spontaneous pneumothorax and a positive family history for the same condition referring to our Institution. The suspicious cases underwent genetic analysis of the BHDS-causative gene FLCN. FLCN-positive cases were further evaluated with routine blood tests, chest radiography, chest CT, abdominal MRI, and dermatological evaluation. RESULTS: Among 114 patients admitted with spontaneous pneumothorax, 7 patients had a family history of pneumothorax, and 6/7 (85.7%) patients had positive genetic test for FLCN as well as 7/13 family members. Pulmonary cysts were found in all patients with a FLCN-positive genetic test. Most patients (10/13, 76.9%) had tiny pulmonary cysts less than 1 cm in diameter. The vast majority of cysts were intraparenchymal (12/13, 92.3%) and located in lower lobes. Dermatological lesions were found in 7/13 (54%) patients, renal cysts in 4/13 (31%) patients, and renal cancer in 1 (1/13, 7.7%) patient. CONCLUSIONS: Although BHDS is considered a rare disease, BHDS underlies spontaneous pneumothorax more often than usually believed, especially whenever a family history of pneumothorax is present. Diagnosis of BHDS is essential to start monitoring patients for the risk of developing renal malignancies.

A Systematic Assessment of Accuracy in Detecting Somatic Mosaic Variants by Deep Amplicon Sequencing: Application to NF2 Gene.

The accurate detection of low-allelic variants is still challenging, particularly for the identification of somatic mosaicism, where matched control sample is not available. High throughput sequencing, by the simultaneous and independent analysis of thousands of different DNA fragments, might overcome many of the limits of traditional methods, greatly increasing the sensitivity. However, it is necessary to take into account the high number of false positives that may arise due to the lack of matched control samples. Here, we applied deep amplicon sequencing to the analysis of samples with known genotype and variant allele fraction (VAF) followed by a tailored statistical analysis. This method allowed to define a minimum value of VAF for detecting mosaic variants with high accuracy. Then, we exploited the estimated VAF to select candidate alterations in NF2 gene in 34 samples with unknown genotype (30 blood and 4 tumor DNAs), demonstrating the suitability of our method. The strategy we propose optimizes the use of deep amplicon sequencing for the identification of low abundance variants. Moreover, our method can be applied to different high throughput sequencing approaches to estimate the background noise and define the accuracy of the experimental design.

Broadening the spectrum of SMARCB1-associated malignant tumors: a case of uterine leiomyosarcoma in a patient with schwannomatosis.

Schwannomatosis is a tumor predisposition syndrome characterized by development of multiple intracranial, spinal, and peripheral schwannomas. Constitutional alterations in either SMARCB1 or LZTR1 on 22q are responsible of the phenotype. We describe a 34-year-old woman who developed multiple benign peripheral sheath tumors and a uterine leiomyosarcoma. The patient carried a de novo constitutional alteration in exon 8 of SMARCB1, c.1118G > A, which destroyed the splice donor site of intron 8. Two schwannomas and the leiomyosarcoma of the patient retained the SMARCB1 mutation; in addition, the tumors showed loss of the normal chromosome 22. In conclusion, our findings enlarged the spectrum of SMARCB1-predisposing tumors and demonstrated, for the first time, the association of a malignant smooth muscle tumor to schwannomatosis. Therefore, clinicians should definitely be aware that a constitutional SMARCB1 mutation, which mainly predisposes to benign nerve sheath tumors, may also predispose to aggressive neoplasms throughout life, within an unexpected spectrum.