BHD mutations, clinical and molecular genetic investigations of Birt-Hogg-Dubé syndrome: a new series of 50 families and a review of published reports

Abstract

Background: Birt-Hogg-Dubé syndrome (BHDS) (MIM 135150) is an autosomal dominant predisposition to the development of follicular hamartomas (fibrofolliculomas), lung cysts, spontaneous pneumothorax, and kidney neoplasms. Germline mutations in BHD are associated with the susceptibility for BHDS. We previously described 51 BHDS families with BHD germline mutations.

Objective: To characterise the BHD mutation spectrum, novel mutations and new clinical features of one previously reported and 50 new families with BHDS.

Methods: Direct bidirectional DNA sequencing was used to screen for mutations in the BHD gene, and insertion and deletion mutations were confirmed by subcloning. We analysed evolutionary conservation of folliculin by comparing human against the orthologous sequences.

Results: The BHD mutation detection rate was 88% (51/58). Of the 23 different germline mutations identified, 13 were novel consisting of: four splice site, three deletions, two insertions, two nonsense, one deletion/insertion, and one missense mutation. We report the first germline missense mutation in BHD c.1978A>G (K508R) in a patient who presented with bilateral multifocal renal oncocytomas. This mutation occurs in a highly conserved amino acid in folliculin. 10% (5/51) of the families had individuals without histologically confirmed fibrofolliculomas. Of 44 families ascertained on the basis of skin lesions, 18 (41%) had kidney tumours. Patients with a germline BHD mutation and family history of kidney cancer had a statistically significantly increased probability of developing renal tumours compared to patients without a positive family history (p = 0.0032). Similarly, patients with a BHD germline mutation and family history of spontaneous pneumothorax had a significantly increased greater probability of having spontaneous pneumothorax than BHDS patients without a family history of spontaneous pneumothorax (p = 0.011). A comprehensive review of published reports of cases with BHD germline mutation is discussed.

Conclusion: BHDS is characterised by a spectrum of mutations, and clinical heterogeneity both among and within families.

Figure 1. BHD mutations newly characterised in families with Birt–Hogg–Dubé syndrome (BHDS). Sequencing chromatograms of genomic DNA from control subjects and patients are shown on the left. The arrows indicate the position of the identified nucleotide changes. The corresponding pedigrees are shown on the right. FF, fibrofolliculoma; MT, mutant; WT, wildtype.

Figure 2. Novel BHD missense mutation (K508R). (A) Genomic sequence of control. (B) Genomic sequence of BHDS patient with the c.1978A>G (K508R) mutation. (C) Multiple sequence alignment. The amino acid residues are coloured according to their chemical properties. (D) Degree of conservation. The numerical index reflects the degree of conservation of the physical–chemical properties in the alignment. Star (*) indicates amino acids 100% identical in the alignment (highest score). The next most conserved group is composed of substitutions in amino acids with the same physical chemical class.

Figure 3. BHD germline mutation reported by the National Cancer Institute (NCI) group and other investigators. (A) Illustration of the 55 germline BHD mutations identified by the NCI. The 23 unique BHD mutations identified in the present study are shown in red. The star indicates mutations identified in both the present study and the previous NCI study. The 22 unique mutations previously reported by NCI are shown in black. (B) Lower panel shows the 18 germline BHD mutations reported by other investigators. ^– Mutations shown in blue were identified by both the NCI group and other investigators. The parenthesis show the original nomenclature used in the original reports.