Identification of a closely linked DNA marker, DXS178, to further refine the X-linked agammaglobulinemia locus

X-linked agammaglobulinemia (XLA) is an inherited recessive disorder in which the primary defect is not known and the gene product has yet to be identified. Utilizing genetic linkage analysis, we previously localized the XLA gene to the map region of Xq21.3-Xq22 with DNA markers DXS3 and DXS17. In this study, further mapping was performed with two additional DNA probes, DXS94 and DXS178, by means of multipoint analysis of 20 families in which XLA is segregating. Thirteen of these families had been previously analyzed with DXS3 and DXS17. Three crossovers were detected with DXS94 and no recombinations were found between DXS178 and the XLA locus in 9 informative families. Our results show that XLA is closely linked to DXS178 with a two-point lod score of 4.82 and a multipoint lod score of 10.24. Thus, the most likely gene order is DXS3-(XLA,DXS178)-DXS94-DXS17, with the confidence interval for location of XLA lying entirely between DXS3 and DXS94. In 2 of these families, we identified recombinants with DXS17, a locus with which recombination had not previously been detected by others in as many as 40 meiotic events. Furthermore, DXS178 is informative in both of these families and does not show recombination with the disease locus. Therefore, our results indicate that DXS178 is linked tightly to the XLA gene.     

The gene for X-linked hydrocephalus maps to Xq28, distal to DXS52.

We report the study of five independent X-linked hydrocephalus (HSAS1) families with polymorphic DNA markers of the Xq28 region. A total of 58 individuals, including 7 living affected males and 22 obligate carriers, have been studied. Maximum lod score was 7.21 at theta = 2.40% for DXS52 (St14-1). A single recombination event was observed between this marker and the HSAS1 locus. Other markers studied were DXS296 (Z = 2.02 at theta = 2.5%), DXS304 (Z = 4.37 at theta = 7.8%), DXS74 (Z = 3.50 at theta = 0%), DXS15 (Z = 1.96 at theta = 5.7%), DXS134 (Z = 3.31 at theta = 0%), and F8C (Z = 5.79 at theta = 0%). These data confirm the localization of the HSAS1 gene to Xq28 and provide evidence for genetic homogeneity of this syndrome. In addition, examination of two obligate recombinant meioses along with multipoint linkage analysis supports the distal localization of the HSAS1 locus with respect to the DXS52 cluster. These observations are of potential interest for future studies aimed at HSAS1 gene characterization.     

Hot spot of recombination within DXS164 in the Duchenne muscular dystrophy gene.

The DMD gene, which spans more than 2,000 kbp, has been assigned to band Xp21 of the X chromosome. Two subclones (PERT 87-1 and PERT 87-15) of the intragenic locus DXS164 physically are separated by approximately 60 kbp. Linkage studies were done in 49 informative DMD families by using the LINKAGE program. Crossing-over between the loci studied occurred in four families. A recombination rate of 4% (support interval [Zmax-1] 1%-10%), which was 54 (support interval 14-135-fold) times higher than expected, was found with a maximum lod score of 13.50. These data suggest a hot spot for recombination within DXS164.     

Localization of a gene for incomplete X-linked congenital stationary night blindness to the interval between DXS6849 and DXS8023 in Xp11.23

Congenital stationary night blindness (CSNB) is a nonprogressive retinal disorder characterized by night blindness, nystagmus, myopia, a variable decrease in visual acuity, an abnormal electroretinographic response, and a disturbance in dark adaptation. Two forms of X-linked CSNB have been defined, complete CSNB in which rod function is extinguished, and incomplete CSNB in which rod function is reduced but not extinguished, as seen by electroretinography and dark adaptometry. In studying a large family of Mennonite ancestry, we have confirmed linkage between the locus (CSNB2) for incomplete CSNB and genetic markers in the Xp11 region. In particular, lod scores of 12.25 and 15.26 at zero recombination were observed between CSNB2 and the markers DXS573 and DXS255. Detailed analysis of critical recombinant chromosomes in this extended family have refined the minimal region for the CSNB2 locus to the interval between DXS6849 and DXS8023 in Xp11.23. Received: 5 November 1997 / Accepted: 23 February 1998     

Linkage analysis of two cloned DNA sequences, DXS197 and DXS207, in hypophosphatemic rickets families

The human X-linked hypophosphatemic rickets gene locus (HYP, formerly HPDR) has been previously localized by linkage analysis to Xp22.31-Xp21.3 and the locus order Xpter-DXS43-HYP-DXS41-Xcen established. Recombination between HYP and these flanking markers is frequently observed and additional markers have been sought. The polymorphic loci DXS197 and DXS207 have been localized to Xpter-Xp11 and Xp22-Xp21, respectively. We have further localized DXS197 to Xpter-Xp21.3 by using a panel of rodent-human hybrid cells and have established the map positions of DXS197 and DXS207 in relation to HYP by linkage studies of hypophosphatemic rickets families. Linkage between DXS197 and the loci DXS43, DXS85, and DXS207 was established with peak lod score values of 6.19, 0 = 0.032; 4.14, 0 = 0.000; and 3.01, 0 = 0.000, respectively. Multilocus linkage analysis mapped the DXS197 and DXS207 loci distal to HYP and demonstrated the locus order Xpter-DXS85-(DXS207, DXS43, DXS197)-HYP-DXS41-Xcen. These additional genetic markers DXS197 and DXS207 will be useful as alternative markers in the genetic counseling of some families.     

A new polymorphic marker very closely linked to DXS52 in the q28 region of the human X chromosome

Summary We have isolated an X chromosome probe, St35.691 (DXS305), which detects two RFLPs with TaqI and PstI, whose combined heterozygosity is about 60%. This probe has been assigned to Xq28 by physical and genetic mapping and is very closely linked to DXS52, DXS15, and the coagulation factor VIII gene (F8C). The best estimate of the recombination fraction for the DXS52-DXS305 interval is 0.014, with a lod score of 50.1. Multipoint analysis places DXS305 on the same side of F8C as DXS52, but complete ordering of the three loci was not possible with our present data. This highly informative marker should be useful in the precise mapping of the many disease genes that have been assigned to the Xq28 band.     

Linkage analysis of families with fragile-X mental retardation, using a novel RFLP marker (DXS 304).

A new polymorphic DNA marker U6.2, defining the locus DXS304, was recently isolated and mapped to the Xq27 region of the X chromosome. In the previous communication we describe a linkage study encompassing 16 fragile-X families and using U6.2 and five previously described polymorphic markers at Xq26-q28. One recombination event was observed between DXS304 and the fragile-X locus in 36 informative meioses. Combined with information from other reports, our results suggest the following order of the examined loci on Xq: cen-F9-DXS105-DXS98-FRAXA-DXS304-(DXS52-F8 -DXS15). The locus DXS304 is closely linked to FRAXA, giving a peak lod score of 5.86 at a corresponding recombination fraction of .00. On the basis of the present results, it is apparent that U6.2 is a useful probe for carrier and prenatal diagnosis in fragile-X families.     

Optic atrophy in Leber hereditary optic neuroretinopathy is probably determined by an X-chromosomal gene closely linked to DXS7.

Leber hereditary optic neuroretinopathy (LHON) is a maternally inherited disease, probably transmitted by mutations in mtDNA. The variation in the clinical expression of the disease among family members has remained unexplained, but pedigree data suggest an involvement of an X-chromosomal factor. We have studied genetic linkage of the liability to develop optic atrophy to 15 polymorphic markers on the X chromosome in six pedigrees with LHON. The results show evidence of linkage to the locus DXS7 on the proximal Xp. Tight linkage to the other marker loci was excluded. Multipoint linkage analysis placed the liability locus at DXS7 with a maximum lod score (Zmax) of 2.48 at a recombination fraction (theta) of .0 and with a Zmax - 1 support interval theta = .09 distal to theta = .07 proximal of DXS7. No evidence of heterogeneity was found among different types of families, with or without a known mtDNA mutation associated with LHON.     

Evidence against an X-linked locus close to DXS7 determining visual loss susceptibility in British and Italian families with Leber hereditary optic neuropathy.

Leber hereditary optic neuropathy (LHON) is associated with mutations of mtDNA, but two features of LHON pedigrees are not explicable solely on the basis of mitochondrial inheritance. There is a large excess of affected males, and not all males at risk develop the disease. These observations could be explained by the existence of an X-linked visual loss susceptibility gene. This hypothesis was supported by linkage studies in Finland, placing the susceptibility locus at DXS7, with a maximum lod score of 2.48 at a recombination fraction of 0. Linkage studies in 1 Italian and 12 British families with LHON, analyzed either together or separately depending on the associated mtDNA mutation, have excluded the presence of such a locus from an interval of about 30 cM around DXS7 in these kindreds, with a total lod score of -26.51 at a recombination fraction of 0.     

Physical mapping of DXS134 close to the DXS52 locus

Summary The locus DXS134 (cpX67) has been physically linked to the cluster of polymorphic loci DXS52, DXS15, and DXS33. A comparison of physical and genetic distance indicates a high rate of recombination in this region.     

Genetic heterogeneity in X-linked amelogenesis imperfecta.

The AMELX gene located at Xp22.1-p22.3 encodes for the enamel protein amelogenin and has been implicated as the gene responsible for the inherited dental abnormality X-linked amelogenesis imperfecta (XAI). Three families with XAI have been investigated using polymorphic DNA markers flanking the position of AMELX. Using two-point linkage analysis, linkage was established between XAI and several of these markers in two families, with a combined lod score of 6.05 for DXS16 at theta = 0.04. This supports the involvement of AMELX, located close to DXS16, in the XAI disease process (AIH1) in those families. Using multipoint linkage analysis, the combined maximum lod score for these two families was 7.30 for a location of AIH1 at 2 cM distal to DXS16. The support interval around this location extended about 8 cM proximal to DXS92, and the AIH1 location could not be precisely defined by multipoint mapping. Study of recombination events indicated that AIH1 lies in the interval between DXS143 and DXS85. There was significant evidence against linkage to this region in the third family, indicating locus heterogeneity in XAI. Further analysis with markers on the long arm of the X chromosome showed evidence of linkage to DXS144E and F9 with no recombination with either of these markers. Two-point analysis gave a peak lod score at DXS144E with a maximum lod score of 2.83 at theta = 0, with a peak lod score in multipoint linkage analysis of 2.84 at theta = 0. The support interval extended 9 cM proximal to DXS144E and 14 cM distal to F9.(ABSTRACT TRUNCATED AT 250 WORDS)     

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).     

Mapping of the gene for X-linked amelogenesis imperfecta by linkage analysis.

X-linked Amelogenesis imperfecta (AI) is a genetic disorder affecting the formation of enamel. In the present study two families, one with X-linked dominant and one with X-linked recessive AI, were studied by linkage analysis. Eleven cloned RFLP markers of known regional location were used. Evidence was obtained for linkage between the AI locus and the marker p782, defining the locus DXS85 at Xp22, by using two-point analysis. No recombination was scored between these two loci in 15 informative meioses, and a peak lod score (Zmax) of 4.45 was calculated at zero recombination fraction. Recombination was observed between the more distal locus DXS89 and AI, giving a peak lod score of 3.41 at a recombination fraction of .09. Recombination was also observed between the AI locus and the more proximal loci DXS43 and DXS41 (Zmax = 0.09 at theta max = 0.31 and Zmax = 0.61 at theta max = 0.28, respectively). Absence of linkage was observed between the AI locus and seven other loci, located proximal to DXS41 or on the long arm of the X chromosome. On the basis of two-point linkage analysis and analysis of crossover events, we propose the following order of loci at Xp22: DXS89-(AI, DXS85)-DXS43-DXS41-Xcen.     

Multipoint linkage analysis in Menkes disease.

Linkage analyses were performed in 11 families with X-linked Menkes disease. In each family more than one affected patient had been diagnosed. Forty informative meioses were tested using 11 polymorphic DNA markers. From two-point linkage analyses high lod scores are seen for DXS146 (pTAK-8; maximal lod score 3.16 at recombination fraction [theta] = .0), for DXS1 (p-8; maximal lod score 3.44 at theta = .0), for PGK1 (maximal lod score 2.48 at theta = .0), and for DXS3 (p19-2; maximal lod score 2.90 at theta = .0). This indicates linkage to the pericentromeric region. Multilocus linkage analyses of the same data revealed a peak for the location score between DXS146(pTAK-8) and DXYS1X(pDP34). The most likely location is between DXS159 (cpX289) and DXYS1X(pDP34). Odds for this location relative to the second-best-supported region, between DXS146(pTAK-8) and DXS159 (cpX289), are better than 74:1. Visualization of individual recombinant X chromosomes in two of the Menkes families showed the Menkes locus to be situated between DXS159(cpX289) and DXS94(pXG-12). Combination of the present results with the reported absence of Menkes symptoms in male patients with deletions in Xq21 leads to the conclusion that the Menkes locus is proximal to DXSY1X(pDP34) and located in the region Xq12 to Xq13.3.     

Mapping of the locus for X-linked cardioskeletal myopathy with neutropenia and abnormal mitochondria (Barth syndrome) to Xq28.

X-linked cardioskeletal myopathy with neutropenia and abnormal mitochondria is clinically characterized by congenital dilated cardiomyopathy, skeletal myopathy, recurrent bacterial infections, and growth retardation. We analyzed linkage between the disease locus and X-chromosomal markers in a family with seven carriers, four patients, and eight unaffected sons of carriers. Highest lod scores obtained by two-point linkage analysis were 2.70 for St14.1 (DXS52, TaqI) at a recombination fraction of zero and 2.53 for cpX67 (DXS134) at a recombination fraction of zero. Multipoint linkage analysis resulted in a maximum lod score of 5.24 at the position of St35.691 (DXS305). The most distal recombination detected in this family was located between the markers II-10 (DXS466) and DX13 (DXS15). These data indicate the location of the mutated gene at Xq28.     

Nance-Horan syndrome: localization within the region Xp21.1-Xp22.3 by linkage analysis.

Nance-Horan Syndrome (NHS) or X-linked cataract-dental syndrome (MIM 302350) is a disease of unknown pathogenesis characterized by congenital cataracts and dental anomalies. We performed linkage analysis in three kindreds with NHS by using six RFLP markers between Xp11.3 and Xp22.3. Close linkage was found between NHS and polymorphic loci DXS43 (theta = 0 with lod score 2.89), DXS41 (theta = 0 with lod score 3.44), and DXS67 (theta = 0 with lod score 2.74), defined by probes pD2, p99-6, and pB24, respectively. Recombinations were found with the marker loci DXS84 (theta = .04 with lod score 4.13), DXS143 (theta = .06 with lod score 3.11) and DXS7 (theta = .09 with lod score 1.68). Multipoint linkage analysis determined the NHS locus to be linked completely to DXS41 (lod score = 7.07). Our linkage results, combined with analysis of Xp interstitial deletions, suggest that the NHS locus is located within or close to the Xp22.1-Xp22.2 region.     

Heterogeneity in X-linked recessive Charcot-Marie-Tooth neuropathy.

Three families presenting with X-linked recessive Charcot-Marie-Tooth neuropathies (CMT) were studied both clinically and genetically. The disease phenotype in family 1 was typical of CMT type 1, except for an infantile onset; two of five affected individuals were mentally retarded, and obligate-carrier females were unaffected. Families 2 and 3 showed distal atrophy with weakness, juvenile onset, and normal intelligence. Motor-nerve conduction velocities were significantly slowed, and electromyography data were consistent with denervation in affected CMT males in all three families. Thirty X-linked RFLPs were tested for linkage studies against the CMT disease loci. Family 1 showed tight linkage (recombination fraction [theta] = 0) to Xp22.2 markers DXS16, DXS143, and DXS43, with peak lod scores of 1.75, 1.78, and 2.04, respectively. A maximum lod score of 3.48 at DXS16 (theta = 0) was obtained by multipoint linkage analysis of the map DXS143-DXS16-DXS43. In families 2 and 3 there was suggestion of tight linkage (theta = 0) to Xq26 markers DXS86, DXS144, and DXS105, with peak lod scores of 2.29, 1.33, and 2.32, respectively. The combined maximum multipoint lod score of 1.81 at DXS144 (theta = 0) for these two families occurred in the map DXS10-DXS144-DXS51-DXS105-DXS15-DXS52++ +. A joint homogeneity analysis including both regions (Xp22.2 and Xq26-28) provided evidence against homogeneity (chi 2 = 9.12, P less than .005). No linkage to Xp11.12-q22 markers was observed, as was reported for X-linked dominant CMT and the Cowchock CMT variant. Also, the chromosomes 1 and 17 CMT loci were excluded by pairwise linkage analysis in all three families.     

Physical and genetic mapping of polymorphic loci in Xq28 (DXS15, DXS52, and DXS134): analysis of a cosmid clone and a yeast artificial chromosome.

Sequences corresponding to the Xq28 loci DXS15, DXS52, DXS134, and DXS130 were shown to be present in a 140-kb yeast artificial chromosome (YAC XY58, isolated by Little et al.). This YAC clone appears to contain a faithful copy of this genomic region, as shown by comparison with human DNA and with a cosmid clone that contains probes St14c (part of the DXS52 sequences) and cpX67 (DXS134). cpX67 and St14c are contained in 11 kb and detect the same MspI RFLP polymorphism. A comparison of the YAC restriction map and pulsed-field gel electrophoresis data leads us to propose the following order of loci: DXS52(VNTR)-DXS33-DXF22S3-DXS130-DXS134 -DXS52-DXS15-DXS52, this whole cluster being comprised within 575 kb. The physical proximity of the DXS15, DXS52, and DXS134 loci led us to reinvestigate recombination events that had been reported between these loci in families from the Centre d'Etude du Polymorphisme Humain. Our results do not support the assumption that this region shows increased recombination.     

Fragile X syndrome: diagnosis using highly polymorphic microsatellite markers.

We describe two highly polymorphic microsatellite AC repeat sequences, VK23AC and VK14AC, which are closely linked to the fragile X at Xq27.3. Both VK23AC (DXS297) and VK14AC (DXS292) are proximal to the fragile site. Two-point linkage analysis in 31 fragile X families gave (a) a recombination frequency of 1% (range 0.00%-4%) with a maximum lod score of 32.04 for DXS297 and (b) a recombination frequency of 7% (range of 3%-15%) with a maximum lod score of 12.87 for DXS292. Both of these polymorphisms are applicable to diagnosis by linkage in families with fragile X syndrome. A multipoint linkage map of genetic markers at Xq27.3 was constructed from genotyping these polymorphisms in the CEPH pedigrees. The DXS292 marker is in the DXS98-DXS297 interval and in 3 cM proximal to DXS297.     

Anderson Fabry disease,a close linkage with highly polymorphic DNA markers DXS17, DXS87 and DXS88

Summary Anderson Fabry disease is an X-linked lysosomal storage disorder caused by α-galactosidase A deficiency. Hemizygous males and some heterozygous females develop renal failure and cardiovacular complications in early adult life. We have investigated six large UK families to assess the possible linkage of five polymorphic DNA probes to the Anderson Fabry locus, previously localised to Xq21-24. No recombination was found between Anderson Fabry disease and DXS87, DXS88 and DXS17, which gave lod_max=6.4,6.4 and 5.8 respectively at θ=0.00, (upper confidence limit 0.10). DXS3 gave lod_max 2.9 at θ=0.10 (upper confidence limit 0.25). DXYS1 was excluded from linkage. The best fit map (DXYS1/DXS3) θ=0.192 (DXS17/DXS87/DXS88/Anderson Fabry locus) provided no information about the order of loci in parentheses due to the absence of recombinants. The close linkage of DXS17, DXS87 and DXS88, together with α-galactosidade A estimation, can be used for antenatal diagnosis and carrier detection until the application of a gene specific probe has been evaluated.