Assignment by deletion mapping of the steroid sulfatase X-linked ichthyosis locus to Xp223

Summary A male child and his mother who are nullisomic and monosomic, respectively, for the distal portion of Xp because of an unbalanced X-Y translocation were tested for steroid sulfatase activity after clinical examination had yielded evidence for ichthyosis in the boy. Deficiency of steroid sulfatase was found in the male patient, while in his mother enzyme levels were in the heterozygous range. These results, based on cytogenetic evidence obtained with an elongation technique, indicate that the STS locus is at Xp223.     

Multipoint linkage analysis of steroid sulfatase (X-linked ichthyosis) and distal Xp markers

Six families with steroid sulfatase deficiency (STS; X-linked ichthyosis) have been studied with the Xg blood group (XG) and the DNA markers dic56 (DXS143), 782 (DXS85), pD2 (DXS43), and GMGX9. Carrier status of females was determined by assay of STS in hair roots. GMGX9 detects a frequent restriction fragment length polymorphism and also identifies a deletion in the majority of families with STS deficiency, including five of the six reported here. The linkage relationship of this marker to the others was studied in normal three-generation families yielding 32 phase-known meioses informative for two or more markers. No recombinants were observed between STS and GMGX9, giving a maximum lod score of 8.73 at zero recombination. Multipoint linkage analysis taking STS and GMGX9 as a single locus and incorporating two-point marker data and STS-XG data from published studies gave the map (Sequence: see text). This order was 2.4 times more likely than with (STS,GMGX9) and dic56 reversed and is supported by our findings in a male with steroid sulfatase deficiency due to a deletion of Xp22.3 which encompasses the XG locus. He is deleted for GMGX9 but shows normal hybridization to dic56 and 782.     

Regional assignment of the gene locus for steroid sulfatase

Summary The gene locus for steroid sulfatase, deficiency of which causes X-linked ichthyosis, is assigned to Xp11Xpter by analysis of 24 man-Chinese hamster somatic cell hybrids. High steroid sulfatase,activity in a hybrid clone having retained only part of Xq is explained by demonstration of an additional late-replicating human X chromosome. This observation confirms previous evidence for noninactivation of the STS locus.     

Linkage analysis in X-linked ichthyosis (steroid sulfatase deficiency)

Summary Linkage analysis has been carried out in nine unrelated families segregating for X-linked ichthyosis (steroid sulfatase deficiency) using seven polymorphic DNA markers from the distal Xp. Close linkage was found between the disease locus and the loci DXS16, DXS89, and DXS143. In all families except one, Southern hybridization with the human steroid sulfatase cDNA and GMGX9 probes showed a deletion of corresponding loci in affected males. Three patients belonging to the same family had no evident deletion with either of the two above-mentioned probes. None of the other six DNA loci included in the linkage analysis were found to be deleted.     

Evidence for a dosage effect at the X-linked steroid sulfatase locus in human tissues.

Steroid sulfatase (STS) is an X-linked enzyme whose locus escapes X inactivation in human somatic cells. STS activity was determined in human fibroblasts varying in X-chromosome number from one to four. Greater STS activity was detected in 2X cell strains when compared to 1X cell strains; however, increased STS activity was not found in 3 and 4X strains as compared with the 2X strains. Greater STS activity was also observed in female hair follicles when compared with male hair follicles. These data provide evidence of a gene dosage effect at the STS locus in human tissues.     

Biochemical evidence for the non-inactivation of the steroid sulfatase locus in human placenta and fibroblasts

Summary Steroid sulfatase activities are significantly higher in placentas obtained after the birth of girls than after the birth of boys, and also in female fibroblasts compared to male strains. This constitutes biochemical evidence for the non-inactivation of the X-linked sulfatase locus. No hydrolytic activity is found in the fibroblasts of ichthyotic boys. Heterozygosity is demonstrated in the fibroblasts of the four mothers studied, as they have steroid sulfatase activity of less or equivalent to the normal male value.     

Long-range physical mapping around the human steroid sulfatase locus

The region of the human X chromosome containing the steroid sulfatase locus was analyzed by pulsed-field gel electrophoresis. Restriction site maps were generated for the X chromosome in the blood of a normal male individual and that in the mouse-human hybrid cell line ThyB-X; these maps extend over approximately 4.3 Mb of DNA of the former, and 3.2 Mb of the latter. Physical linkage was defined between the STS locus and sequences detected by the probes GMGX9 (DXS237), GMGXY19 (DYS74), CRI-S232 (DXS278), and dic56 (DXS143), and the order telomere--(STS, DYS74)--DXS237--DXS278--DXS143--centromere was deduced. The pulsed-field maps were used to demonstrate a deletion of 180 kb of DNA from the X chromosome of an individual with X-linked ichthyosis. Also, possible locations for the Kallmann syndrome gene were revealed, and the distance between the steroid sulfatase locus and the pseudoautosomal region was estimated to be at least 4 Mb.     

X-linked steroid sulfatase: Evidence for different gene-dosage in males and females

Summary Steroid sulfatase (STS) activities in female fibroblast strains are significantly higher than in male strains, as determined by cleavage of dehydroepiandrosterone sulfate. The difference is probably not due to hormonal control of gene expression, but suggests that for this X-linked locus there is no gene dosage compensation.     

The human X-linked steroid sulfatase gene and a Y-encoded pseudogene: evidence for an inversion of the Y chromosome during primate evolution

The mammalian X and Y chromosomes are thought to have evolved from a common, nearly homologous chromosome pair. Although there is little sequence similarity between the mouse or the human X and Y, there are several regions in which moderate to extensive sequence homologies have been found, including, but not limited to, the so-called pseudoautosomal segment, in which X-Y pairing and recombination take place. The steroid sulfatase gene is in the pseudoautosomal region of the mouse, but not in man. We have cloned and characterized the human STS X-encoded locus and a pseudogene that is present on the long arm of the Y chromosome. Our data in humans and other primates suggest that there has been a pericentric inversion of the Y chromosome during primate evolution that has disrupted the former pseudoautosomal arrangement of these genes. These results provide additional insight into the evolution of the sex chromosomes and into the nature of this interesting portion of the human genome.     

Genetic heterogeneity of steroid sulfatase deficiency revealed with cDNA for human steroid sulfatase

Three cDNA clones with inserts of 1.2-1.6 kb that reacted both with antibodies and oligonucleotides specific for steroid sulfatase were isolated from a human placental library in lambda gt11. The 5'-end of one of the inserts, STS-3, was sequenced and colinearity with the amino acid sequence of 3 peptides of steroid sulfatase encompassing 64 amino acids was demonstrated. STS-3 hybridized with 2.5, 4.6 and 6.3 kb species in poly(A)+RNA and with 2.5, 4 and 9 kb fragments of EcoRI digested human DNA. The frequency of the EcoRI fragments in DNA from females was approximately twice that in DNA from males. DNA from two patients with steroid sulfatase deficiency and X-linked ichthyosis did not hybridize with STS-3. DNA from a third patient showed a normal hybridization pattern. It is concluded that steroid sulfatase deficiency is a genetically heterogenous disorder.     

Oto-palato-digital syndrome type I: further evidence for assignment of the locus to Xq28

Summary The oto-palado-digital syndrome (OPD) is a rare X-linked disease with diagnostic skeletal features, conduction deafness, cleft palate and mild mental retardation. Differences in clinical presentation between families have led investigators to classify OPD into two subtypes: type I and type II. A linkage study performed in one family segregating for OPD I has recently suggested linkage to three marker loci: DXS15, DXS52 at Xq28, and DXS86 at Xq26. We have investigated an additional OPD I family for linkage by using distal chromosome Xq DNA probes. The linkage data and the analysis of recombination events that have occurred in this family excluded, definitively, the Xq26 region for OPD I, and provide further support for mapping the mutant gene close to the cluster of tightly linked markers DXS15, DXS52 and DXS305 at Xq28.     

A sensitive and dependable assay for distinguishing hamster and human X-linked steroid sulfatase activity in somatic cell hybrids

Summary A radioisotopic assay is described to distinguish between Chinese hamster and human steroid sulfatase activity in extracts prepared from hamsterxhuman somatic cell hybrids. This assay is based on different pH optima and provides a sensitive and unambiguous biochemical marker for the short arm of the human X chromosome and as well as for otherwise genetically inactivated X chromosomes in rodentxhuman hybrids.     

Genetic complementation of steroid sulphatase after somatic cell hybridization of X-linked ichthyosis and multiple sulphatase deficiency

Summary Complementation studies of steroid sulphatase were carried out in the heterokaryon population of fibroblasts derived from patients with X-linked ichthyosis and multiple sulphatase deficiency. The activity of steroid sulphatase of the fused cell population was constantly higher (approximately 2–5 fold) than that of the unfused cocultivated cells. The occurrence of complementation further supports the hypothesis that at least two different loci control the expression of steroid sulphatase in the human genome.     

Cloning of the rat steroid sulfatase gene (Sts), a non-pseudoautosomal X-linked gene that undergoes X inactivation

Although the human steroid sulfatase (STS) gene has been cloned and characterized in detail, several attempts to clone its mouse homologue, with either anti-human STS antibodies or human STS cDNA probes, have failed, suggesting a substantial divergence between these genes. However, partial amino-terminal sequence from purified rat liver STS is very similar to its human counterpart, and sequence comparisons have revealed several domains that are conserved among all the sulfatases characterized to date. Thus, we used a degenerate-primer RT-PCR approach to amplify a 321-bp fragment from rat liver cDNA, which was used as a probe to clone and characterize the complete cDNA. Comparison of the protein coding region between the rat and human genes showed 66% homology both at the DNA and the protein levels. STS activity was conferred to STS(−) A9 cells upon transfection with a rat Sts expression construct, indicating the authenticity of the cloned cDNA. While Sts has been shown to be located in the mouse pseudoautosomal region, both physical and genetic mapping demonstrate that Sts is not pseudoautosomal in the rat. The overall genomic organization of rat Sts and human STS is very similar, except that the insertion site for intron 1 in the rat is 26 bp upstream from that in the human. Rat Sts is only 8.2 kb long, while the human STS spans over 146 kb. Received: 24 October 1995 / Accepted: 5 March 1996     

Further evidence for a silent allele in the transferrin locus of the horse

A silent allele in the transferrin locus (Tf) was observed in a Thoroughbred mare and in five of her offspring from three different matings. Evidence for the silent allele was obtained by quantitative immunodiffusion studies.     

New fluorogenic substrate for the first continuous steroid sulfatase assay

The screening for new inhibitors of steroid sulfatase requires an efficient test system. To overcome the shortcomings of the available discontinuous fluorimetric assay, several coumarin-type compounds were investigated as potential new substrates. 3,4-Benzocoumarin 7-O-sulfate was found to have appropriate substrate properties for the establishment of the first direct continuous assay of steroid sulfatase.     

Localization of the properdin structural locus to Xp11.23-Xp21.1

Properdin is a serum protein belonging to the alternative pathway of complement activation whose absence is often associated with fatal bacterial infections. Properdin deficiency segregates with an X-linked recessive pattern and its position has been recently refined by genetic linkage analysis to the proximal part of the X-chromosome short arm near the OTC and DXS7 loci. We have hybridized an 0.8-kb genomic clone encoding part of the human properdin gene to a panel of somatic cell hybrids retaining different portions of the human X chromosome and thereby localized the probe to Xcen-Xp21.1. Furthermore, in situ hybridization of the same probe to replication banded metaphase chromosomes refined this localization to the region Xp11.23-Xp21.1 (with a peak grain distribution in the region equivalent to Xp11.4). As OTC and DXS7 map to Xp21.1 and Xp11.3, respectively, the data presented here strongly suggest that the X-linked deficiency syndrome is due to a defect in the locus encoding the structural properdin gene or in a physically close regulatory locus.     

A long range restriction map of the distal human X chromosome short arm around the steroid sulfatase locus.

The distal short arm of the human X chromosome is of interest because it contains genes which escape X chromosome inactivation and because it is subject to frequent deletions in human patients. The steroid sulfatase gene has been particularly well studied as an example of a gene which escapes X inactivation and which is included in a number of these deletion events. For these reasons a physical map of the region around the STS gene would be of interest. We have constructed a rare cutting enzyme map of this area and have determined the position of several nearby markers with respect to STS. We have also oriented the 5' and 3' ends of the STS gene on this map and have determined the centromeric and telomeric portions of the region. Finally, we have shown that this map can be used to locate deletion breakpoints in STS deficient patients.