Genetic mapping of anhidrotic ectodermal dysplasia: DXS159, a closely linked proximal marker

Summary Three families with anhidrotic ectodermal dysplasia (AED) have been studied by linkage analysis with seven polymorphic DNA markers from the Xp11-q21 region. Previously reported linkage to DXYS1 (Xq13-q21) has been confirmed (z()=4.08 at =0.05) and we have also established linkage to another polymorphic locus, DXS159, located in Xq11-q12 (z()=4.28 at =0.05). Physical mapping places DSX159 proximal to the Xq12 breakpoint of an X autosome translocation found in a female with clinical signs of ectodermal dysplasia. Of all markers that have been used in linkage analysis of AED, DXS159 would appear the closest on the proximal side of the disease locus.     

Linkage analysis with RFLPs in families with androgen resistance syndromes: evidence for close linkage between the androgen receptor locus and the DXS1 segment

Summary Three families with androgen resistance syndromes — two with testicular feminization and one with Reifenstein syndrome — have been studied for linkage analysis. Using three cloned DNA sequences from the centromere region and the proximal long arm of the X chromosome (p8, pDP34, and S9, which define respectively the chromosomal segments DXS1, DXYS1, and DXS17), we found no recombination between the DXS1 locus and the mutant genes in the three families. Assuming that these disorders are the result of allelic mutations at the same locus for the androgen receptor, we can conclude that there is a close linkage between DXS1 and the androgen receptor locus, with a maximum lod score =3.5 at a recombination fraction =0.0 using the LIPED program (Ott 1974).     

Linkage studies do not confirm the cytogenetic location of incontinentia pigmenti on Xp11

Summary Linkage studies have been performed in 5 incontinentia pigmenti (IP) families totaling 29 potentially informative meioses. Ten probes of the Xp arm were used, six of them were precisely localized on the X chromosome, using hamster x human somatic cell hybrids containing a broken X chromosome derived from an incontinentia pigmenti patient carrying an X;9 translocation [46,XX,t(X;9)(p11.21;q34)]. The following order for probes is proposed: pter-(DXS7, DXS146, DXS255)-IP1-(DXS14, DXS90)-DXS106-qter. The negative lod scores obtained exclude the possibility that in the families studied, the gene for IP is located in Xp11 or in the major part of the Xp arm.     

A linkage study of Emery-Dreifuss muscular dystrophy

Summary We have searched for linkage between polymorphic loci defined by DNA markers on the X chromosome and X-linked Emery-Dreifuss muscular dystrophy (EDMD). There are high recombination rates between EDMD and the Xp loci known to be linked to Becker and Duchenne muscular dystrophy. There is a suggestion of linkage between EDMD and the loci DXS52 and DXS15, defined by probes St 14 and DX13 respectively, located at Xq28. for DXS15=1.14 at =0.15. This is in agreement with the previously reported linkage between a disorder strongly resembling EDMD and colour-blindness (Thomas et al. 1972), suggesting that there is a second locus on the X chromosome concerned with muscle integrity.     

Choroideremia: linkage analysis with physically mapped close DNA-markers

Summary We report linkage studies in 18 choroideremia (TCD) families using four closely linked polymorphic markers. Probe pZ11, which is known to be deleted in several unrelated patients with TCD, showed no recombinations (z _max 15.63 at = 0.00). In contrast, one recombination was observed with DXS367, which is also physically very close to TCD. Loci DXS95 and DXYS69 each showed more than one recombination with TCD. Moreover, these analyses revealed a double crossover between TCD and DXYS1, changing the previously reported very close linkage to a recombination fraction of 0.04 with a lod score of 9.93. Multipoint linkage analysis placed TCD proximal to DXS95-DXYS69 and very close to DXS367-pZ11 with almost identical multipoint lod score maxima either proximal to DXS367 (z _max= 23.43) or proximal to pZ11 (z _max=23.36). These results provide a refined linkage map around TCD and will also be useful in DNA diagnostics of the disease.     

Linkage studies of the Wiskott-Aldrich syndrome: polymorphisms at TIMP and the X chromosome centromere are informative markers for genetic prediction

Summary Eleven families segregating for the X-linked recessive immune deficiency disorder, Wiskott-Aldrich syndrome (WAS), were studied by linkage analysis with an alpha satellite DNA probe, pBamX-7, which detects polymorphism at the X chromosome centromere, locus DXZ1, as well as three other polymorphic markers defining loci on the proximal short arm of the X chromosome. Linkage has been established between WAS and DXZ1 ( ()=7.08 at =0.03) and WAS and the TIMP gene locus ( ()=5.09 at =0.0). We have also confirmed close linkage between DXZ1 and two marker loci, DXS14 and DXS7, previously shown to be linked to the WAS locus. The probe pBamX-7 detected allelic variation in all females tested, reflecting the high frequency of polymorphism at the centromere. One WAS carrier revealed a recombination between WAS and both marker loci DXZ1 and DXS14, indicating that WAS does not map between these loci. In conjunction with previous data from genetic mapping studies of WAS, these results confirm the pericentromerix Xp localization of WAS and demonstrate the usefulness of alpha satelite DNA probes as tools for genetic prediction in WAS as well as other pericentric X-linked diseases.     

Localization of the gene for Wieacker-Wolff syndrome in the pericentromeric region of the X chromosome

The Wieacker-Wolff syndrome (WWS, MIM* 314580), first described clinically in 1985, is an X-linked recessive disorder. In earlier studies, linkage between the WWS gene and DXYS1 at Xq21.2 and DXS1 at Xq11 as well as AR at Xq12 was reported. Here we report on a linkage analysis using highly polymorphic, short terminal repeat markers located in the segment from Xp21 to Xq24. No recombination between the WWS locus and ALAS2 or with AR (z = 4.890 at θ = 0.0) was found. Therefore, the WWS locus was assigned to a segment of approximately 8 cM between PFC (Xp11.3–Xp 11.23) and DXS339 (Xq11.2–Xq13). Received: 14 March 1997 / Accepted: 9 April 1997     

The Localization of a Gene Causing X-Linked Cleft Palate and Ankyloglossia (CPX) in an Icelandic Kindred Is between DXS326 and DXYS1X

The locus responsible for X-linked, nonsyndromic cleft palate and/or ankyloglossia (CPX) has previously been mapped to the proximal long arm of the human X chromosome between Xq21.31 and q21.33 in an Icelandic kindred. We have extended these studies by analyzing an additional 14 informative markers in the family as well as including several newly investigated family members. Recombination analysis indicates that the CPX locus is more proximal than previously thought, within the interval Xq21.1-q21.31. Two recombinants place DXYS1X as the distal flanking marker, while one recombinant defines DXS326 as the proximal flanking marker, an interval of less than 5 cM. Each of the flanking markers recombines with the CPX locus, giving 2-point lod scores of Z_max = 4.16 at θ = 0.08 (DXS326) and Z_max = 5.80 at θ = 0.06 (DXYS1X).     

Deletion of the pseudoautosomal region and lack of sex-chromosome pairing at pachytene in two infertile men carrying an X;Y translocation

Two males with a 46,Y,der(X),t(X;Y)(p22.3;q11) complement were referred independently for evaluation of sterility with azoospermia. Both patients exhibited minimal symptomatology, characterized only by psychological disturbances. Study of X-chromosome breakpoints with pseudoautosomal probes 68B (DXYZ2 elements), 113D (locus DXYS15), and 19B (locus MIC2) indicated in both patients that at least 97% of the X pseudoautosomal sequences are lost. Hybridization with Xp22.3-specific probes DXS283, DXS284, and DXS31 shows that these loci are retained on the rearranged chromosome. Thus, the X-chromosome breakpoints are located close to the proximal boundary of the pseudoautosomal region, between MIC2 and DXS284.     

Assignment of the gene for complete X-linked congenital stationary night blindness (CSNB1) to Xp11.3

X-linked congenital stationary night blindness (CSNB) is a nonprogressive retinal disorder characterized by a presumptive defect of neurotransmission between the photoreceptor and bipolar cells. Carriers are not clinically detectable. A new classification for CSNB includes a complete type, which lacks rod function by electroretinography and dark adaptometry, and an incomplete type, which shows some rod function on scotopic testing. The refraction in the complete CSNB patients ranges from mild to severe myopia; the incomplete ranges from moderate hyperopia to moderate myopia. To map the gene responsible for this disease, we studied eight multigeneration families, seven with complete CSNB (CSNB1) and one with incomplete CSNB, by linkage analysis using 17 polymorphic X-chromosome markers. We found tight genetic linkage between CSNB1 and an Xp11.3 DNA polymorphic site, DXS7, in seven families with CSNB1 (LOD 7.35 at theta = 0). No recombinations to CSNB1 were found with marker loci DXS7 and DXS14. The result with DXS14 may be due to the small number of scored meioses (10). No linkage could be shown with Xq loci PGK, DXYS1, DXS52, and DXS15. Pairwise linkage analysis maps the gene for CSNB1 at Xp11.3 and suggests that the CSNB1 locus is distal to another Xp11 marker, TIMP, and proximal to the OTC locus. Five-point analysis on the eight families supported the order DXS7-CSNB1-TIMP-DXS225-DXS14. The odds in favor of this order were 9863:1. Removal of the family with incomplete CSNB (F21) revealed two most favored orders, DXS7-CSNB1-TIMP-DXS255-DXS14 and CSNB1-DXS7-TIMP-DXS255-DXS14. Heterogeneity testing using the CSNB1-M27 beta and CSNB1-TIMP linkage data (DXS7 was not informative in F21) was not significant to support evidence of genetic heterogeneity (P = 0.155 and 0.160, respectively).     

X-linked hypohidrotic ectodermal dysplasia: DNA probe linkage analysis and gene localization

Summary A linkage study of 24 families with hypohidrotic (anhidrotic) ectodermal dysplasia (HED) has been performed. The previously suggested linkage to DXYS1 has been confirmed, and linkage to probes DXS14 and DXS3 has been established. We suggest that the HED locus lies in the centromeric region between DXYS1 on the long arm and DXS14 on the short arm of the X chromosome, probably on proximal Xq.     

Haplotype and multipoint linkage analysis in Finnish choroideremia families

Summary Multipoint linkage analysis of choroideremia (TCD) and seven X chromosomal restriction fragment length polymorphisms (RFLPs) was carried out in 18 Finnish TCD families. The data place TCD distal to PGK and DXS72, very close to DXYS1 and DXYS5 (Zmax = 24 at = 0) and proximal to DXYS4 and DXYS12. This agrees with the data obtained from other linkage studies and from physical mapping. All the TCD males and carrier females studied have the same DXYS1 allele in coupling with TCD. In Northeastern Finland, 66/69 chromosomes carrying TCD had the same haplotype at loci DXS72, DXYS1, DXYS4, and DXYS12. The same haplotype is seen in only 15/99 chromosomes not carrying TCD. Moreover, in 71/104 non-TCD chromosomes, the haplotype at six marker loci is different from those seen in any of the 76 TCD chromosomes. This supports the previously described hypothesis that the large Northern Finnish choroideremia pedigrees, comprising a total of over 80 living patients representing more than a fifth of all TCD patients described worldwide, carry the same mutation. These linkage and haplotype data provide improved opportunities for prenatal diagnosis based on RFLP studies.     

Linkage analysis in X-linked ocular albinism.

We studied the linkage of X-linked Nettleship-Falls ocular albinism (OA1) to Xp22.1-Xp22.3 RFLPs at 12 loci in five families, including one in which OA1 cosegregates with a deletion of steroid sulfatase (STS). We found evidence for tight linkage of OA1 to the Xp22.3 loci DXS143, STS, and DXS452. DXS452, a newly described polymorphism detected by the probe E25B1.8, is part of the sequence family "DXS278" (pCRI-S232), but represents a single genetic locus. Every female in this study was heterozygous for the DXS452 RFLP. Thus, this marker will be extremely useful for family studies and genetic counseling. Analysis of individual recombinations suggests that OA1 maps between DXS143 and DXS85. Multipoint linkage analysis was consistent with this localization but was not statistically significant. These data suggest that OA1 lies proximal to the deletion in a previously described family with OA1 and STS deletion, but maps within the Xp22.3-Xp22.2 region.     

X-linked cleft palate: the gene is localized between polymorphic DNA markers DXYS12 and DXS17

Summary The gene involved in an X-linked form of cleft palate has been finely mapped using 14 restriction fragment length polymorphic (RFLP) markers that cover the long arm of the X chromosome. By the combination of deletion mapping and linkage analysis, the gene has been localized between the anonymous DNA markers DXYS12 on the proximal side, and DXS17 distally.     

Exclusion mapping of the gene for X-linked neural tube defects in an Icelandic family

Various polymorphic markers with a random distribution along the X chromosome were used in a linkage analysis performed on a family with apparently Xlinked recessive inheritance of neural tube defects (NTD). The lod score values were used to generate an exclusion map of the X chromosome; this showed that the responsible gene was probably not located in the middle part of Xp or in the distal region of Xq. A further refining of these results was achieved by haplotype analysis, which indicated that the gene for X-linked NTD was located either within Xp21.1-pter, distal from the DMD locus, or in the region Xq12–q24 between DXS106 and DXS424. Multipoint linkage analysis revealed that the likelihood for gene location is highest for the region on Xp. The region Xq26–q28, which has syntenic homology with the segment of the murine X chromosome carrying the locus for bent tail (Bn), a mouse model for X-linked NTD, is excluded as the location for the gene underlying X-linked NTD in the present family. Thus, the human homologue of the Bn gene and the present defective gene are not identical, suggesting that more than one gene on the X chromosome plays a role in the development of the neural tube.     

Nance-Horan syndrome: linkage analysis in 4 families refines localization in Xp22.31–p22.13 region

Nance-Horan syndrome (NHS) is an X-linked disease characterized by severe congenital cataract with microcornea, distinctive dental findings, evocative facial features and mental impairment in some cases. Previous linkage studies have placed the NHS gene in a large region from DXS143 (Xp22.31) to DXS451 (Xp22.13). To refine this localization further, we have performed linkage analysis in four families. As the maximum expected Lod score is reached in each family for several markers in the Xp22.31–p22.13 region and linkage to the rest of the X chromosome can be excluded, our study shows that NHS is a genetically homogeneous condition. An overall maximum two-point Lod score of 9.36 (θ = 0.00) is obtained with two closely linked markers taken together, DXS207 and DXS1053 in Xp22.2. Recombinant haplotypes indicate that the NHS gene lies between DXS85 and DXS1226. Multipoint analysis yields a maximum Lod score of 9.45 with the support interval spanning a 15-cM region that includes DXS16 and DXS1229/365. The deletion map of the Xp22.3–Xp21.3 region suggests that the phenotypic variability of NHS is not related to gross rearrangement of sequences of varying size but rather to allelic mutations in a single gene, presumably located proximal to DXS16 and distal to DXS1226. Comparison with the map position of the mouse Xcat mutation supports the location of the NHS gene between the GRPR and PDHA1 genes in Xp22.2. Received: 14 June 1996 / Revised: 10 October 1996     

Localization of the gene for the Wiskott-Aldrich syndrome between two flanking markers, TIMP and DXS255, on Xp11.22-Xp11.3.

The Wiskott-Aldrich syndrome (WAS) is an X-linked recessive genetic disease in which the basic molecular defect is unknown. We previously located the WAS gene between two DNA markers, DXS7 (Xp11.3) and DXS14 (Xp11), and mapped it to the proximal short arm of the human X chromosome (Kwan et al., 1988, Genomics 3:39-43). In this study, further mapping was performed on 17 WAS families with two additional RFLP markers, TIMP and DXS255. Our data suggest that DXS255 is closer to the WAS locus than any other markers that have been previously described, with a multipoint maximum lod score of Z = 8.59 at 1.2 cM distal to DXS255 and thus further refine the position of the WAS gene on the short arm of the X chromosome. Possible locations for the WAS gene are entirely confined between TIMP (Xp11.3) and DXS255 (Xp11.22). Use of these markers thus represents a major improvement in genetic prediction in WAS families.     

Mapping of the gene for X-chromosomal split-hand/split-foot anomaly to Xq26–q26.1

A large inbred kindred from Pakistan in which an isolated type of split-hand/split-foot anomaly is transmitted as an X-chromosomal trait has previously been described. An X/autosomal translocation and an X-chromosomal rearrangement have been excluded by cytogenetic studies. In order to map the gene responsible for this disorder, linkage analysis has been performed by using 14 highly polymorphic DNA markers distributed over the whole X chromosome. Two-point linkage analysis between the disease locus and X-chromosomal marker loci gives maximal lod scores at = 0.00 with the loci DXS294 (Z _max= 5.13) and HPRT (Z _max= 4.43), respectively, suggesting that the gene for the X-chromosomal split-hand/split-foot anomaly is localized at Xq26–q26.1.     

A primary genetic map of the pericentromeric region of the human X chromosome

We report a genetic linkage map of the pericentromeric region of the human X chromosome, extending from Xp11 to Xq13. Genetic analysis with five polymorphic markers, including centromeric alpha satellite DNA, spanned a distance of approximately 38 cM. Significant lod scores were obtained with linkage analysis in 26 families from the Centre d'Etude du Polymorphisme Humain, establishing estimates of genetic distances between these markers and across the centromere. Physical mapping experiments, using a panel of somatic cell hybrids segregating portions of the X chromosome due to translocations or deletions, are in agreement with the multilocus linkage analysis and indicate the order Xp11 . . . DXS7(L1.28)-TIMP- DXZ1(alpha satellite, cen)- DXS159(cpX73)-PGK1 . . . Xq13. The frequency of recombination in the two approximately 20-cM intervals flanking alpha satellite on either chromosome arm was roughly proportional to the estimated physical distance between markers; no evidence for a reduced crossover frequency was found in the intervals adjacent to the centromere. However, significant interfamilial variations in recombination rates were noted in this region. This primary map should be useful both as a foundation for a higher resolution centromere-based linkage map of the X chromosome and in the localization of genes to the pericentromeric region.     

An interstitial duplication of the X chromosome in a male allows physical fine mapping of probes from the Xq13-q22 region

Summary An insertional translocation into the proximal long arm of the X chromosome in a boy showing muscular hypotony, growth retardation, psychomotor retardation, cryptorchidism, and Pelizaeus-Merzbacher disease (PMD) was identified as a duplication of the Xq21–q22 segment by employing DNA probes. With densitometric scanning for quantitation of hybridization signals, 15 Xq probes were assigned to the duplicated region. Analysis of the duplication allowed us to dissect the X-Y homologous region physically at Xq21 and to refine the assignments of the loci for DXYS5, DXYS12, DXYS13, DXS94, DXS95, DXS96, DXS111, and DXS211. Furthermore, we demonstrated the presence of two different DXYS13, and DXS17 alleles in genomic DNA of our patient, suggesting that the duplication resulted from a meiotic recombination event involving the two maternal X chromosomes.