Investigation of the Birt-Hogg-Dube tumour suppressor gene (FLCN) in familial and sporadic colorectal cancer.

BACKGROUND Birt-Hogg-Dubé (BHD) syndrome is an autosomal dominant multisystem disorder with skin (fibrofolliculomas or trichodiscomas), lung (cysts and pneumothorax) and kidney (renal cell carcinoma) tumours. Although colorectal neoplasia was reported initially to be part of the BHD phenotype, some recent studies have not confirmed this association. METHODS A series of clinical and laboratory studies was undertaken to investigate possible relationships between colorectal neoplasia and the BHD gene (FLCN). The studies investigated whether individuals with familial colorectal cancer of unknown cause might have unsuspected germline FLCN mutations, looked for somatic FLCN C(8) tract mutations in microsatellite unstable sporadic colorectal cancers, and assessed the risk of colorectal neoplasia and possible genotype-phenotype correlations in BHD patients. RESULTS Although it was found previously that germline FLCN mutations can be detected in approximately 5% of patients with familial renal cell carcinoma, germline FLCN mutations were not detected in 50 patients with familial non-syndromic colorectal cancer. Analysis of genotype-phenotype correlations for two recurrent FLCN mutations identified in a subset of 51 families with BHD demonstrated a significantly higher risk of colorectal neoplasia in c.1285dupC mutation (within the exon 11 C(8) mononucleotide tract) carriers than in c.610delGCinsTA mutation carriers (chi(2)=5.78, p=0.016). Somatic frameshift mutations in the FLCN exon 11 C(8) mononucleotide tract were detected in 23% of sporadic colorectal cancers with microsatellite instability, suggesting that FLCN inactivation might contribute to colorectal tumourigenesis. CONCLUSIONS These findings suggest that the previously reported clinical heterogeneity for colorectal neoplasia may reflect allelic heterogeneity and the risk of colorectal neoplasia in BHD syndrome requires further investigation.

A new locus-specific database (LSDB) for mutations in the folliculin (FLCN) gene.

Birt-Hogg-Dubé syndrome (BHD) is an autosomal dominant condition characterised by the presence of facial fibrofolliculomas, pulmonary cysts which may be associated with spontaneous pneumothorax and renal tumours. Germline mutations in the gene Folliculin (FLCN) were first identified in BHD patients in 2002. In addition FLCN mutations have also been described in families with isolated primary spontaneous pneumothorax (PSP) and also familial clear cell renal carcinomas (FcRCC). We have established a locus-specific database based on the Leiden Open (source) Variation Database (LOVD) software. The version of the database contains 60 previously published mutations and 10 previously unpublished novel germline FLCN mutations. The mutations are comprised of deletions (44.3%), substitutions (35.7%), duplications (14.3%) and deletion/insertions (5.7%). The database is accessible online at http://www.lovd.nl/flcn.

Multiplex ligation-dependent probe amplification (MLPA) analysis is an effective tool for the detection of novel intragenic PLA2G6 mutations: implications for molecular diagnosis.

Phospholipase associated neurodegeneration (PLAN) comprises a heterogeneous group of autosomal recessive neurological disorders caused by mutations in the PLA2G6 gene. Direct gene sequencing detects approximately 85% mutations in infantile neuroaxonal dystrophy. We report the novel use of multiplex ligation-dependent probe amplification (MLPA) analysis to detect novel PLA2G6 duplications and deletions. The identification of such copy number variants (CNVs) expands the PLAN mutation spectrum and may account for up to 12.5% of PLA2G6 mutations. MLPA should thus be employed to detect CNVs of PLA2G6 in patients who show clinical features of PLAN but in whom both disease-causing mutations cannot be identified on routine sequencing.

Diffuse cystic lung disease of unexplained cause with coexistent small airway disease: a possible causal relationship?

Diffuse "true" cystic lung disease is rare, and the specificity of high-resolution computed tomography (HRCT) has reduced the need for biopsy. We present 5 patients with similar clinical and HRCT features of cystic lung disease that were sufficiently atypical to warrant surgical lung biopsies that showed coexistent small airway diseases (SAD). There were 4 female patients and 1 male patient with a mean age of 43 years. All were never smokers. Four had symptoms such as dyspnea (1), cough (2), or both (1). HRCTs showed variably sized thin-walled cystic airspaces without zonal distribution, some with prominent vessels in their walls. One case was unilateral. Surgical lung biopsy showed cystic change comprising localized loss of alveolar density with coexistent SADs [chronic bronchiolitis (n=2), eosinophilic bronchiolitis, probable asthma (n=1), and diffuse idiopathic neuroendocrine cell hyperplasia (n=2)]. Two patients who were tested for Birt-Hogg-Dube-related gene mutations proved negative, and all lacked other features of Birt-Hogg-Dube. We hypothesize that chronic damage to small airways may lead to cystic degeneration in a minority of patients. Precedents in relation to Sjogren syndrome and hypersensitivity pneumonitis raise the possibility of a causal association between pathologies in these 2 anatomic compartments, although HRCT data in relation to common SADs indicate that this would be a rare phenomenon. The driving factor remains unknown.