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To the Editor:It was with great interest that we read the article by de la Torre et al. (1) that examined the question of whether acrochordons are a component of the Birt-Hogg-Dubé syndrome (BHDS). In an addendum, the authors mentioned our recently published study in which we equated BHDS with the Hornstein-Knickenberg syndrome (HKS) (2). We should like to make a few remarks we consider pertinent. De la Torre et al. wrote that we assigned the perifollicular fibroma to the trichodiscoma-fibrofolliculoma spectrum. This, however, was not the case. All we said was that, due to the plane sectioned, fibrofolliculomas and trichodiscomas are often misinterpreted as perifollicular fibromas. In our opinion, perifollicular fibroma does not belong to the spectrum of skin lesions in BHDS/HKS. In common with other authors before us (3), we believe that true perifollicular fibroma is identical with fibrous papule of the face.De la Torre et al. cast doubt on an association of multiple fibrofolliculomas and trichodiscomas with other pathological findings, and thus called into question whether BHDS/HKS is truly a syndrome. Since colonic polyps are commonly found in the general population, too, it is possible that the frequently found coincidence of BHDS/HKS with colonic polyps does not necessarily provide evidence of a syndromic association. However, a frequent association of familial renal tumors with BHDS/HKS was recently reported (4,5). Because, in contrast to colonic polyps, both inheritable renal tumors and multiple fibrofolliculomas and trichodiscomas are extremely rare, we believe that their concomitant occurrence underscores the syndromic nature of BHDS/HKS. Furthermore, the repeatedly reported association of the skin lesions with pulmonary conditions, in particular pneumothorax and bronchiectasis, which are also rare, is striking (2). We recently reported on such an association (6). The concept that BHDS/HKS is a syndrome thus appears justified, although, of course, this needs to be confirmed by further molecular-genetic investigations.Tilman Schulz M.D.Wolfgang Hartschuh M.D.