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.     

Genetic mapping of X-linked albinism-deafness syndrome (ADFN) to Xq26.3-q27.1

X-linked albinism-deafness syndrome (ADFN) was described in one Israeli Jewish family and is characterized by congenital nerve deafness and piebaldness. The ADFN mutation probably affects the migration of neural crest-derived precursors of the melanocytes. As a first step toward identifying the ADFN gene, a linkage study was performed to localize the disease locus on the X chromosome. The family was found to be informative for 11 of 107 RFLPs along the X, and two-point analysis showed four of them--factor 9 (F9), DXS91, DXS37, and DNF1--to have definite or suggestive linkage with ADFN. Multipoint linkage analysis indicated two possible orders within this cluster of loci, neither of which was preferable. In both orders F9 was the most distal, and the best estimate for the location of ADFN was between F9 and the next proximal marker (8.6 cM from F9 [Z = 8.1] or 8.3 cM from F9 [Z = 7.9]). These results suggest that the ADFN is at Xq26.3-q27.1. Disagreement between our data and previous localization of DXS91 at Xq11-q13 was resolved by hybridization of the probe pXG-17, which detects the DXS91 locus, to a panel of somatic cell hybrids containing different portions of the X chromosome. This experiment showed that this locus is definitely at Xq24-q26. Together with the linkage data, our results place DXS91 at Xq26 and underscore the importance of using more than one mapping method for the localization of molecular probes.     

X-linked progressive mixed deafness: a new microdeletion that involves a more proximal region in Xq21.

We report a large two-generation pedigree with seven affected males segregating for an X-linked mixed conductive sensorineural deafness. The patients present with atypical Mondini-like dysplasia, dilated petrous facial canal, dilatation of the internal auditory meatus fully connected with enlarged cochlear canals, and, in one patient, a wide bulbous posterior labyrinth. Obligatory carrier females are mildly affected. Molecular characterization of this family revealed a deletion of locus DXS169, in Xq21.1. Loci DXS72 and DXS26, which, respectively, flank DXS169 proximally and distally, were intact. Since a gene responsible for X-linked progressive mixed deafness with perilymphatic gusher (DFN3) has previously been assigned by deletion mapping to a slightly more distal interval between DXS26 and DXS121, this study indicates either two different deafness genes or the involvement of a very large region in Xq21.     

The gene for X-linked progressive mixed deafness with perilymphatic gusher during stapes surgery (DFN3) is linked to PGK

Summary A linkage analysis has been performed in a large Dutch kindred with progressive mixed deafness with perilymphatic gusher during stapes surgery (DFN3) using a panel of X-chromosomal RFLPs. Tight linkage (z_max=3.07 at =0.00) was demonstrated with the locus for phosphoglycerate kinase (PGK), which is located at Xq13. Tight linkage was excluded for DXS9 (probe RC8) and DXS41 (probe 99.6) on Xp and for blood clotting factor 9 (FIX) on distal Xq. Deafness is one of the predominant clinical features in males with deletions of the Xq21 band. Our results suggest that this association may be due to involvement of the DFN3 gene.     

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.     

Linkage of the gene for an X-linked mental retardation disorder to a hypervariable (AGAT)n repeat motif within the human hypoxanthine phosphoribosyltransferase (HPRT) locus (Xq26).

We recently reported a new X-linked mental retardation (XLMR) disorder in a four-generation family of Dutch descent. Features included Dandy-Walker malformation, basal ganglia disease, and seizures. Twenty-six family members, including two living affected males and two obligate carriers, were available for study. No evidence of linkage was observed between the disease locus and RFLPs from several X-chromosome regions, including Xp21-p22 (13 markers), proximal Xq (four markers), and Xq28 (three markers). However, a new hypervariable short tandem repeat (STR) within the HPRT gene at Xq26 showed positive linkage to the disease locus, with a maximum lod score of 2.19 at a recombination fraction of 0. A second hypervariable marker in Xq26, the dinucleotide repeat XL90A3 (DXS425), showed a lod score of .84 at a recombination fraction of .11. Both the HPRT and DXS425 markers were typed in 40 CEPH families, and subsequent multipoint linkage analysis showed the following order: Xcen-DXS425-(HPRT,XLMR)-F9-qter. HPRT and these flanking markers are therefore useful for carrier detection and prenatal diagnosis in this family. This study illustrates that hypervariable STRs will be powerful tools for linkage analysis and genetic diagnosis, particularly when relatively small families are involved.     

Genetic Linkage Heterogeneity in Myotubular Myopathy

Myotubular myopathy is a severe congenital disease inherited as an X-linked trait (MTM1; McKusick 31040). It has been mapped to the long arm of chromosome X, to the Xq27-28 region. Significant linkage has subsequently been established for the linkage group comprised of DXS304, DXS15, DXS52, and F8C in several studies. To date, published linkage studies have provided no evidence of genetic heterogeneity in severe neonatal myotubular myopathy (XLMTM). We have investigated a family with typical XLMTM in which no linkage to these markers was found. Our findings strongly suggest genetic heterogeneity in myotubular myopathy and indicate that great care should be taken when using Xq28 markers in linkage studies for prenatal diagnosis and genetic counseling.     

Multipoint linkage analysis of loci in the proximal long arm of the human X chromosome: application to mapping the choroideremia locus.

Choroideremia (McK30310), an X-linked retinal dystrophy, causes progressive night blindness, visual field constriction, and eventual central blindness in affected males by the third to fourth decade of life. The biochemical basis of the disease is unknown, and prenatal diagnosis is not available. Subregional localization of the choroideremia locus to Xq13-22 was accomplished initially by linkage to two restriction-fragment-length polymorphisms (RFLPs), DXYS1 (Xq13-q21.1) and DXS3 (Xq21.3-22). We have now extended our linkage analysis to 12 families using nine RFLP markers between Xp11.3 and Xq26. Recombination frequencies of 0%-4% were found between choroideremia and five markers (PGK, DXS3, DXYS12, DXS72, and DXYS1) located in Xq13-22. The families were also used to measure recombination frequencies between RFLP loci to provide parameters for the program LINKMAP. Multipoint analysis with LINKMAP provided overwhelming evidence for placing the choroideremia locus within the region bounded by DXS1 (Xq11-13) and DXS17 (Xq21.3-q22). At a finer level of resolution, multipoint analysis suggested that the choroideremia locus was proximal to DXS3 (384:1 odds) rather than distal to it. Data were insufficient, however, to distinguish between a gene order that puts choroideremia between DXS3 and DXYS1 and one that places choroideremia proximal to both RFLP loci. These results provide linkage mapping of choroideremia and RFLP loci in this region that will be of use for further genetic studies as well as for clinical applications in this and other human diseases.     

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.     

Tightly linked flanking markers for the Lowe oculocerebrorenal syndrome, with application to carrier assessment.

The Lowe oculocerebrorenal syndrome (OCRL) is characterized by congenital cataract, mental retardation, and defective renal tubular function. A map assignment of OCRL to Xq24-q26 has been made previously by linkage analysis with DXS42 at Xq24-q26 (theta = 0, z = 5.09) and with DXS10 at Xq26 (theta = 0, z = 6.45). Two additional families were studied and three additional polymorphisms were identified at DXS42 by using a 35-kb sequence isolated with the probe detecting the original polymorphism at DXS42. With additional OCRL families made informative for DXS42, theta remained 0 with z = 6.63; and for DXS10 theta = 0.03 and z = 7.07. Evidence for placing OCRL at Xq25 also comes from a female with Lowe syndrome and an X;3 translocation. We have used the Xq25 breakpoint in this patient to determine the position of OCRL relative to the two linked markers. Each derivative chromosome was isolated away from its normal counterpart in somatic cell hybrids. DXS42 was mapped to the derivative chromosome X containing Xpterq25, and DXS10 was mapped to the derivative chromosome 3 containing Xq25-qter. The markers DXS10 and DXS42 therefore show tight linkage with OCRL in six families and flank the Xq25 breakpoint in a female patient with an X;3 translocation. Linkage analysis with flanking markers was used to assess OCRL carrier status in women at risk. Results, when compared with carrier determination by ophthalmologic examination, indicated that the slit-lamp exam can be a sensitive and specific method of carrier determination in many cases.     

Physical fine mapping of the choroideremia locus using Xq21 deletions associated with complex syndromes

Characterization of several male-viable deletions and duplications with 20 random DNA probes has enabled us to subdivide the Xq21 region into seven discernible intervals. Almost all of the deletions spanning part of Xq21 are associated with choroideremia and mental retardation, with deafness being another common feature. The gene locus for choroideremia was assigned to interval 3 spanning the loci DXS95, DXS165, and DXS233. Genes for X-linked deafness and mental retardation were tentatively assigned to interval 2. Deletions of intervals 4 through 7 were not associated with any clinical abnormality. We have constructed a preliminary long-range restriction map of intervals 2 and 3 using field-inversion gel electrophoresis. The DXS232, DXS121, and DXS233 loci are located on the same SfiI fragment, whereas the DXS165 and DXS95 loci could not be linked to this cluster using SfiI and SalI.     

DXS26 (HU16) is located in Xq21.1

Summary We have localized a single-copy DNA probe, HU16 (locus DXS26), to Xq21.1. The probe was isolated from a human-mouse hybrid X;13 library and mapped with human-mouse hybrids containing different portions of the human X chromosome and DNA from male patients with different X-chromosomal deletions. The following order of loci is proposed: Xcen-(DXS72, DXS169)-(DXS232,DXS26)-DXS121-DXS233-DXS165 TCD-DXS95-DXYSl-Xqter. HU16 will be useful in the study of the putative genes that reside in Xq21 and whose defects lead to deafness and mental retardation.     

Genetic heterogeneity in X-linked hydrocephalus: linkage to markers within Xq27.3.

X-linked hydrocephalus is a well-defined disorder which accounts for > or = 7% of hydrocephalus in males. Pathologically, the condition is characterized by stenosis or obliteration of the aqueduct of Sylvius. Previous genetic linkage studies have suggested the likelihood of genetic homogeneity for this condition, with close linkage to the DXS52 and F8C markers in Xq28. We have investigated a family with typical X-linked aqueductal stenosis, in which no linkage to these markers was present. In this family, close linkage was established to the DXS548 and FRAXA loci in Xq27.3. Our findings demonstrate that X-linked aqueductal stenosis may result from mutations at two different loci on the X chromosome. Caution is indicated in using linkage for the prenatal diagnosis of X-linked hydrocephalus.     

Isolation and characterization of a highly polymorphic human locus (DXS455) in proximal Xq28

Human Xq28 is highly gene dense with over 27 loci. Because most of these genes have been mapped by linkage to polymorphic loci, only one of which (DXS52) is informative in most families, a search was conducted for new, highly polymorphic Xq28 markers. From a cosmid library constructed using a somatic cell hybrid containing human Xq27.3----qter as the sole human DNA, a human-insert cosmid (c346) was identified and found to reveal variation on Southern blot analyses with female DNA digested with any of several different restriction endonucleases. Two subclones of c346, p346.8 and p346.T, that respectively identify a multiallelic VNTR locus and a frequent two-allele TaqI polymorphism were isolated. Examination of 21 unrelated females showed heterozygosity of 76 and 57%, respectively. These two markers appeared to be in linkage equilibrium, and a combined analysis revealed heterozygosity in 91% of unrelated females. Families segregating the fragile X syndrome with key Xq28 crossovers position this locus (designated DXS455) between the proximal Xq28 locus DXS296 (VK21) and the more distal locus DXS374 (1A1), which is proximal to DXS52. DXS455 is therefore the most polymorphic locus identified in Xq28 and will be useful in the genetic analysis of this gene dense region, including the diagnosis of nearby genetic disease loci by linkage.     

The Juberg-Marsidi syndrome maps to the proximal long arm of the X chromosome (Xq12-q21).

Juberg-Marsidi syndrome (McKusick 309590) is a rare X-linked recessive condition characterized by severe mental retardation, growth failure, sensorineural deafness, and microgenitalism. Here we report on the genetic mapping of the Juberg-Marsidi gene to the proximal long arm of the X chromosome (Xq12-q21) by linkage to probe pRX214H1 at the DXS441 locus (Z = 3.24 at theta = .00). Multipoint linkage analysis placed the Juberg-Marsidi gene within the interval defined by the DXS159 and the DXYS1X loci in the Xq12-q21 region. These data provide evidence for the genetic distinction between Juberg-Marsidi syndrome and several other X-linked mental retardation syndromes that have hypogonadism and hypogenitalism and that previously. Finally, the mapping of the Juberg-Marsidi gene is of potential interest for reliable genetic counseling of at-risk women.     

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.     

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     

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.     

Myotubular Myopathy in a Girl with a Deletion at Xq27-q28 and Unbalanced X Inactivation Assigns the MTMI Gene to a 600-kb Region

A young girl with a clinically moderate form of myotubular myopathy was found to carry a cytogenetically detectable deletion in Xq27-q28. The deletion had occurred de novo on the paternal X chromosome. It encompasses the fragile X (FRAXA) and Hunter syndrome (IDS) loci, and the DXS304 and DXS455 markers, in Xq27.3 and proximal Xq28. Other loci from the proximal half of Xq28 (DXS49, DXS256, DXS258, DXS305, and DXS497) were found intact. As the X-linked myotubular myopathy locus (MTM1) was previously mapped to Xq28 by linkage analysis, the present observation suggested that MTM1 is included in the deletion. However, a significant clinical phenotype is unexpected in a female MTM1 carrier. Analysis of inactive X-specific methylation at the androgen receptor gene showed that the deleted X chromosome was active in ~80% of leukocytes. Such unbalanced inactivation may account for the moderate MTM1 phenotype and for the mental retardation that later developed in the patient. This observation is discussed in relation to the hypothesis that a locus modulating X inactivation may lie in the region. Comparison of this deletion with that carried by a male patient with a severe Hunter syndrome phenotype but no myotubular myopathy, in light of recent linkage data on recombinant MTM1 families, led to a considerable refinement of the position of the MTM1 locus, to a region of ~600 kb, between DXS304 and DXS497.     

Refinement of linkage of human severe combined immunodeficiency (SCIDX1) to polymorphic markers in Xq13.

The most common form of human severe combined immunodeficiency (SCID) is inherited as an X-linked recessive genetic defect, MIM 300400. The disease locus, SCIDX1, has previously been placed in Xq13.1-q21.1 by demonstration of linkage to polymorphic markers between DXS159 and DXS3 and by exclusion from interstitial deletions of Xq21.1-q21.3. We report an extension of previous linkage studies, with new markers and a total of 25 SCIDX1 families including female carriers identified by nonrandom X chromosome inactivation in their T lymphocytes. SCIDX1 was nonrecombinant with DXS441, with a lod score of 17.96. Linkage relationships of new markers in the SCIDX1 families were consistent with the linkage map generated in the families of the Centre d'Etude du Polymorphisme Humain (CEPH) and with available physical map data. The most likely locus order was DXS1-(DXS159,DXS153)-DXS106-DXS132-DXS4 53-(SCIDX1,PGK1, DXS325,DXS347,DXS441)-DXS447-DXS72-DXYS 1X-DXS3. The SCIDX1 region now spans approximately 10 Mb of DNA in Xq13; this narrowed genetic localization will assist efforts to identify gene candidates and will improve genetic management for families with SCID.