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Heiko Traupe, Universitäts-Hautklinik, Von-Esmarch-Strasse 56, D–4400 Münster (FRG); Rudolf Happle, Department of Dermatology, University of Nijmegen, Javastraat 104, NL-6524 Nijmegen (The Netherlands) Sir, The data of Unamuno et al. [8] on the high incidence of cryptorchidism in X-linked recessive ichthyosis are of considerable interest, in particular to those concerned with pediatric dermatology. For an affected boy the sequels of untreated cryptorchidism may be far more serious than the ichthyosis. Following our report [7] on this association dealing with seven instances of cryptorchidism out of a series of 25 patients with X-linked recessive ichthyosis, and a recent communication of Lykkesfeldt et al. [2] on 9 cases of testicular maldescent among 76 such patients and 3 additional affected patients with normally descended gonads who developed testis cancer, this is now the the third study confirming a high frequency of cryptorchidism in Xlinked recessive ichthyosis, reporting 9 cases out of a series of 22 patients [8]. How can the apparent association of cryptorchidism and X-linked recessive ichthyosis be explained? The simplest answer is to consider testicular maldescent a further manifestation of steroid sulfatase deficiency. Even in the absence of cryptochidism patients with X-linked recessive ichthyosis exhibit an abnormal androgen and estrogen metabolism that is characterized by elevated levels of LH and estrone sul-fate, a lack of decline of dehydroepiandrosterone sulfate in older age, and low androstenedione and estradi-ol levels [3]. Surprisingly, testosterone remains normal. This is probably due to the compensatory increase of LH [3]. LH plays an important role in normal testicular descent as is evidenced by the usual effectiveness of a HCG treatment. Therefore it is conceivable that testicular descent in X-linked recessive ichthyosis may require higher LH levels than in normal persons and that in some of the patients the LH levels will not be sufficient. A second possible mechanism giving rise to cryptorchidism in X-linked recessive ichthyosis are cytoge-netic aberrations involving the short arm of the X-chromosome such as X-Y translocations [4,6] or the loss of the distal part of the short arm of the X-chromosome (Xp-) [1, 5]. In these cases, secondary steroid sulfatase deficiency occurs due to deletion of the steroid sulfatase gene. These deletions usually also involve genes in the neighborhood of the steroid sulfatase gene. Therefore patients with such a cytogenetic aberration present with a broad spectrum of associated symptoms such as cryptorchidism, hypogenitalism, mental retardation and even anosmia with hypogona-dotropic hypogonadism (Kallman syndrome). These deletions are inherited in a dominant pattern and their expressivitiy in female carriers is rather low [1, 4– 6]. Due to a founder effect they are most likely not distributed evenly in larger populations,