I found this article on the Emedicine website, its easier to access ifyou type in emedicine and then RUD in your search bar, rather than registering with the site. KALLMANS at the ame site might also interest you. This and Kallmans is linked to XLI. You can have RUD and KALLMANS without having X linked ichthyosis, however it mainly occurs together. I think from the research I have been readng about, that there are so many variations of the "X" chromosome, that XLI can sometimes (and rarely) produce additional symptoms. Most men and boys that have XLI only have dry skin and no other symptoms.
Background: Rud syndrome, previously considered a rare recessive disorder marked by ichthyosis, hypogonadism, mental retardation, epilepsy, and dwarfism, is now classified as an ichthyosis. The contemporary ichthyosis classification reassigns it as a neuroichthyosis with cutaneous findings most similar to those observed in X-linked recessive ichthyosis, rather than a distinct clinical entity. Although ichthyosis and hypogonadism are the predominant features, neurologic deficits vary, suggesting genetic heterogeneity.
Pathophysiology: The pathophysiology of Rud syndrome is unknown. Defects in steroid sulfatase and Kallman loci on the X chromosome have been identified; however, these defects were not tested in most of the earlier cases. Cases suggestive of an autosomal recessive inheritance pattern have also been reported.
Internationally: The prevalence is rare worldwide.
Mortality/Morbidity: Mortality and morbidity depend on the presence and the severity of associated findings.
Race: No racial predilection is known.
Sex: Cases in which steroid sulfatase deficiency has been identified involved boys; however, overall, no male predilection is apparent, as anticipated by an X-linked recessive genodermatosis. This observation could be explained by the fact that a defect in an autosomal recessive gene may also be present (some cases suggestive of this inheritance pattern have been reported) or that such heterogeneity of clinical and genetic findings exists and some patients who are thought to have Rud syndrome really have different disorders manifesting with clinical changes similar to those of Rud syndrome.
Age: The disease manifests with clinical signs and symptoms at birth or shortly thereafter.