Regional localization on the human X of DNA segments cloned from flow sorted chromosomes

[Early diagnosis of retinoblastoma: usefulness of searching for RB1 gene mutations]

BACKGROUND

Retinoblastoma, the intraocular malignancy most common in children,occurs in both familial and sporadic (bilateral or unilateral). Hereditary predisposition is caused by a germ-line mutation while non-hereditary is due to two somatic mutations in a retinal cell. This work was carried out in order to analyse genetically, the high number of families with some affected member and to go deep into the molecular mechanisms responsible of this pathology.

PATIENTS AND METHOD

59 families with one or more affected members were analysed. Cytogenetics and with polymorphic markers studies were carried out and a search for mutations was performed in DNA from white cells and from available tumoral tissue.

RESULTS

In four of the 5 familial cases, the responsible mutation was established,the same as in 9 of the 13 bilateral sporadic. In the 7% of the unilateral sporadic cases, mutation was found in leucocytary DNA. Lost of heterozygosity as a second mutational event was mainly due to mitotic recombination.

CONCLUSIONS

Among the mutations of our series, a higher frequency of punctual mutations,responsible of the first mutational event, was observed at constitutional level. Lost of heterozygosity was the mechanism observed in the majority of the tumours.

Juvenile X-linked retinoschisis from XLRS1 Arg213Trp mutation with preservation of the electroretinogram scotopic b-wave

PURPOSE

To present an Arg213Trp missense mutation in the XLRS1 gene in a family with juvenile X-linked retinoschisis in which one affected male had a normal electroretinogram scotopic b-wave amplitude.

METHODS

Two affected males and one unaffected male from this family with X-linked retinoschisis underwent standard clinical examination including an electroretinogram. Mutations in the XLRS1 gene were detected by sequence analysis and by restriction enzyme assay for loss of an MSP-I restriction site.

RESULTS

A missense mutation of C to T at nucleotide position 637 was identified in exon 6 of the XLRS1 gene. This changed the positively charged arginine to a nonpolar tryptophan (Arg213Trp) within the biologically important discoidin domain. Clinical examination revealed intraretinal cysts in a spoke-wheel distribution and early macular atrophy of the retinal pigment epithelium. Whereas the older affected patient had an "electronegative" electroretinogram typical of retinoschisis, the 13-year-old grandson with the same XLRS1 mutation had a normal electroretinogram scotopic b-wave.

CONCLUSION

Although the electroretinogram is a key diagnostic test for X-linked retinoschisis, this report of a normal electroretinogram scotopic b-wave in a male with molecularly confirmed X-linked retinoschisis indicates that caution is advised in relying on the electroretinogram in differential diagnosis of this condition.

Linkage analysis in Usher syndrome type I (USH1) families from Spain

Usher syndrome (USH) is an autosomal recessive hereditary disorder characterised by congenital sensorineural hearing loss and gradual visual impairment secondary to retinitis pigmentosa (RP). The disorder is clinically and genetically heterogeneous. With regard to Usher type I (USH1), several subtypes have been described, the most frequent being USH1B located on chromosome 11q13.5. Of 18 USH1 families studied by linkage analysis, 12 (67%) showed significant lod score values for locus D11S527 (Zmax=14.032, theta=0.000) situated on chromosome 11q. Our findings suggest considerable genetic heterogeneity in the Spanish USH1 population. It is important to note that one of our families linked to the USH1B locus shows interesting intrafamilial clinical variability. As regards the remaining six USH1 families, the linkage analysis did not provide conclusive data, although two of them show slight linkage to markers located on chromosome 3q (Zmax=1.880, theta=0.000 for D3S1279), the same location that had previously been assigned to some USH3 families.

Polymorphism of alcohol dehydrogenase genes in alcoholic and nonalcoholic individuals from Valencia (Spain)

Polymorphisms in the two variable ADH loci (ADH2 and ADH3) were analyzed in two groups (alcoholics and nonalcoholics) from a Spanish population. The frequencies were similar to those reported for other Causcasian groups. ADH2-1 and ADH3-1 genotypes were more frequent in alcoholics than in nonalcoholics, but the differences were not significant.

Genetics of retinoblastoma: a study

We have analyzed 43 families with either familial retinoblastoma (RB) (four kindreds), bilateral sporadic RB (10 individuals), or unilateral sporadic RB (29 individuals). Genetic studies focused on karyotype analysis, loss of heterozygosity of intragenic polymorphisms, and search for point mutations. We have been able to identify the genetic defect underlying the disease in eight cases. Deletions have been found in three patients with sporadic RB, two bilateral in one of which karyotyping had previously detected an interstitial deletion of chromosome 13 affecting (q13-q31) and one unilateral. Five different point mutations were responsible for three cases of bilateral sporadic RB, one case of bilateral sporadic RB, and one case of bilateral familial RB. The low frequency of constitutional mutations found in our study has led us to review and evaluate the possibilities and limitations of the present genetic analyses on RB and to access the different factors influencing the detection of mutations causing the disease, because genetic counseling is mainly based on mutation identification.

Correlation between connexin 32 gene mutations and clinical phenotype in X-linked dominant Charcot-Marie-Tooth neuropathy

We studied the relationship between the genotype and clinical phenotype in 27 families with dominant X-linked Charcot-Marie-Tooth (CMTX1) neuropathy. Twenty-two families showed mutations in the coding region of the connexin32 (cx32) gene. The mutations include four nonsense mutations, eight missense mutations, two medium size deletions, and one insertion. Most missense mutations showed a mild clinical phenotype (five out of eight), whereas all nonsense mutations, the larger of the two deletions, and the insertion that produced frameshifts showed severe phenotypes. Five CMTX1 families with mild clinical phenotype showed no point mutations of the cx32 gene coding region. Three of these families showed positive genetic linkage with the markers of the Xq13.1 region. The genetic linkage of the remaining two families could not be evaluated because of their small size.

Sorsby's fundus dystrophy in a family with a Ser-181-CVS mutation in the TIMP-3 gene: poor outcome after laser photocoagulation

PURPOSE

Mutations in the TIMP-3 (tissue inhibitor of metalloproteinase-3) gene can cause Sorsby's fundus dystrophy (SFD) and lead to choroidal neovascular membrane (CNV) formation. We studied a large American family of Irish Protestant descent with CNV inherited as an autosomal dominant trait, to determine the phenoptype and to learn whether a mutation was present in TIMP-3.

METHODS

Twelve members of 5 generations were evaluated clinically, with psychophysical and electroretinographic testing, and by fluorescein angiography. Blood samples for DNA extraction were obtained from 21 affected and unaffected family members and from 1 unrelated spouse. DNA sequence was determined, and affected individuals showed a Ser-181-Cys mutation in TIMP-3 exon 5.

RESULTS

Observable pathology involved primarily the macula, and both the full-field ERG and visual fields were normal. Acute CNV occurred during the third through fifth decades, with second eyes typically also affected during the subsequent year. Three affected members complained of nyctalopia prior to developing CNV. A Ser-181-Cys mutation in the TIMP-3 gene cosegregated with CNV in 10 affected subjects but was absent in 3 relatives at risk and sufficiently old to trust the clinical designation of normalcy. Nine eyes of 6 family members were treated by laser photocoagulation by 5 different ophthalmologists for foveal and juxtafoveal CNV. All eyes had recurrent CNV and lost acuity to 20/300 or less within several months.

CONCLUSIONS

Laser photocoagulation of CNV did not stem vision loss in this SFD family. Although possible benefits of laser treatment were not put to formal clinical trial owing to the limited number of Sorsby's cases, it appears that photocoagulation is not of long-term benefit for preserving vision loss from the TIMP-3 Ser-181-Cys mutation. Several younger family members with the mutation are thus far not clinically affected and are being followed up.

Disruption of conserved rhodopsin disulfide bond by Cys187Tyr mutation causes early and severe autosomal dominant retinitis pigmentosa

PURPOSE

To determine the molecular basis of an early and severe form of autosomal dominant retinitis pigmentosa and to characterize the associated phenotype.

METHODS

Visual function evaluation included electrophysiologic and psychophysical testing. Molecular genetic analysis included determining the DNA sequence of sections of the rhodopsin gene amplified by polymerase chain reaction and screening for changes single-nucleotide by allele-specific oligonucleotide hybridization.

RESULTS

Affected family members are heterozygous for a unique Cys187Tyr rhodopsin mutation which disrupts a highly conserved disulfide bond essential to normal rhodopsin function. The retinitis pigmentosa (RP) phenotype includes early and severe retinal dysfunction. The full-field electroretinogram showed only negligible remaining rod and cone responses by 22 years of age. Visual fields were constricted severely by early middle-age years. Macular dysfunction caused reduced visual acuity in early adult years, and macular atrophy was present in older age. The severity of phenotype generally correlated with age, with the exception of an affected 44-year-old patient who had better visual acuity, fields, electroretinogram, and dark-adapted thresholds than did three younger affected relatives, ranging in age from 22 to 38 years.

CONCLUSION

An early onset, blinding form of autosomal dominant RP results from a rhodopsin Cys187Tyr mutation that eliminates a residue necessary for the formation of a highly conserved disulfide bond essential to normal rhodopsin function. The fact that one family member is significantly less affected than his younger relatives suggests that genetic or environmental factors can modulate the phenotype.

Charcot-Marie-Tooth neuropathies: from clinical description to molecular genetics

Ninety-five families with Charcot-Marie-Tooth (CMT) neuropathies were studied clinically, electrophysiologically (MNCVs and EMGs), and by molecular genetics. Fifty-four families (56.8%) were type 1A mapped at 17p11.2-p12 and DNA duplication was present in 50 (92.6% of CMT1A families). One family with type 1B (1.1%) mapped at 1q22-q23 showed a point mutation of the myelin P0 gene. Eighteen families (18.9%) were type CMT2 based on electrophysiological studies. Molecular genetics was not yet conclusive. Twenty CMT families were with X-linked dominant inheritance (CMTX1) (21.1%) mapped at Xq13.1 and connexin 32 (CX32) point mutations were present in 15 families (75%) (five nonsense mutations, eight missense mutations, two deletions). Two CMT families (2.1%) with X-linked recessive inheritance showed no point mutations of CX32 and their mapping was different from CMTX1, respectively at Xp22.2 for CMTX2 and at Xq26 for CMTX3.

The identification of polymorphic microsatellite loci in the horse and their use in thoroughbred parentage testing

Six new horse microsatellite loci were identified by sequencing M13 clones containing horse genomic inserts which gave positive signals when probed with a CA/GT repeat probe. Oligonucleotide primer pairs were synthesized for these loci and for two previously described horse microsatellites, HTG4 and HTG6. Polymerase chain reaction assays were then carried out on a panel of 20 different unrelated Thoroughbred horse DNAs. DNAs from eight cases of double covering which could not be solved by conventional blood typing were also examined. Several of the loci amplified were found to be polymorphic and, using a limited subset of primers, a clear exclusion could be established for one of the stallions in five of the cases. DNA typing is therefore a useful adjunct to blood typing in the horse and indeed, in the future will probably replace it.

Mapping of a gene for autosomal dominant juvenile-onset open-angle glaucoma to chromosome Iq

A large Caucasian family is presented, in which a juvenile-onset form of open-angle glaucoma is transmitted in an autosomal dominant fashion. Sixteen affected family members were identified from 31 at-risk individuals descended from the affected founder. Affected patients developed high intraocular pressures (sometimes > 40 mm Hg) within the first 2 decades of life. Linkage analysis between the disease phenotype and 12 microsatellite repeat markers located on chromosome 1q gave a maximum lod score of 8.38 at a recombination fraction of zero for marker D1S210. Analysis of recombinant haplotypes suggests a total inclusion region of about 14 cM between markers D1S194 and D1S218 at 1q21-q31. This represents the second juvenile-glaucoma family, in which the disease has been mapped to the long arm of chromosome 1.

Screening of dominantly inherited Charcot-Marie-Tooth neuropathies

Sixty-three families with dominantly inherited Charcot-Marie-Tooth (CMT) neuropathies including 730 subjects (total) from which 356 affected were studied clinically, electrophysiologically (MNCVs and EMGs), by genetic linkage, and screened for DNA duplication. Thirty-eight families (60.3%) were type 1A (demyelinating CMT mapped on chromosome 17). DNA duplication was present in 36 families (94.8% of CMT1A families). One CMT1A family (2.6%) showed no duplication but suggested genetic linkage with markers of chromosome 17. One CMT1A family (2.6%) revealed nonduplication in some affected members and duplication in other affected members. The disease in that family segregated with the same chromosome 17 markers regardless of duplication status. The other CMT families with dominant inheritance but without duplication included one family with CMT1B (demyelinating CMT mapped on chromosome 1) (1.6%), 14 families with CMT2 axonal neuropathy (22.2%), and 10 families with X-linked dominant CMT (15.9%).

Nicotinic neuronal acetylcholine receptor alpha-3 subunit transcription in normal and myasthenic thymus

Thymic transcription of the alpha-3 subunit of the AChR was studied through sequencing and PCR analysis of thymic cDNA clones, Northern blotting, and ribonuclease protection assays. This analysis revealed at least three, 3' end sequence variants for the alpha-3 subunit as well as a variant that results from the alternative splicing of an antisense 122 bp Alu sequence between exons 5 and 6 of the normal transcript. The spliced Alu sequence not only shifts the exon 6 reading frame but also carries an in-frame stop codon. If translated, this variant transcript would produce a truncated peptide lacking the fourth transmembrane domain of the subunit and carrying a carboxy terminus dodecapeptide not found in any other known AChR subunit sequence. The putative variant subunit may lack biological activity and should differ antigenically from its normal counterpart. In comparing the normal, the MG hypertrophic, and the MG thymoma for transcription of the alpha-3 subunit and its 122 bp variant, it was found that there were no qualitative or quantitative changes in alpha-3 transcript expression in the MG hypertrophic thymi. Thymomas, however, showed an overall decrease in alpha-3 transcription and a comparative increase in beta-amyloid precursor transcription. The decrease in the levels of alpha-3 transcription in thymomas may be related to the proliferation of thymic epithelial cells.

Construction and characterization of partial digest DNA libraries made from flow-sorted human chromosome 16

In this report, we present the techniques used for the construction of chromosome-specific partial digest libraries from flow-sorted chromosomes and the characterization of two such libraries from human chromosome 16. These libraries were constructed to provide materials for use in the development of a high-resolution physical map of human chromosome 16, and as part of a distributive effort on the National Laboratory Gene Library Project. Libraries with 20-fold coverage were made in Charon-40 (LA16NL03) and in sCos-1 (LA16NC02) after chromosome 16 was sorted from a mouse-human monochromosomal hybrid cell line containing a single homologue of human chromosome 16. Both libraries are approximately 90% enriched for human chromosome 16, have low nonrecombinant backgrounds, and are highly representative for human chromosome-16 sequences. The cosmid library in particular has provided a valuable resource for the isolation of coding sequences, and in the ongoing development of a physical map of human chromosome 16.

Multipoint mapping of adult onset polycystic kidney disease (PKD1) on chromosome 16

Analysis of genetic linkage data in 33 adult onset polycystic kidney (ADPKD) families was carried out using probes for the D16S85, D16S84, and D16S94 loci. The data set of 33 families shows no evidence of genetic heterogeneity since one unlinked family was previously excluded. Two point linkage analysis showed maximum likelihood values of the recombination fraction of 0.07 for ADPKD and D16S85 (lod score 18.78), 0.02 for ADPKD and D16S84 (lod score 7.55), and 0.00 for ADPKD and D16S94 (lod score 6.73). Multipoint analysis showed a maximum likelihood order of tel-D16S85-0.06-D16S84-0.02-(PKD1, D16S94)-cen with a multipoint lod score of 32.16. Analysis of rare recombinants lying close to PKD1 gave results consistent with this order.

A novel GC-rich human macrosatellite VNTR in Xq24 is differentially methylated on active and inactive X chromosomes

A new X chromosome-specific repetitive sequence, a 3 kilobase HindIII clone with a base composition of 63% C+G, has been isolated. The sequence is organized as a hypervariable tandem repeat cluster ranging in size from 150-350 kilobases, with outlying single copies. This locus, designated DXZ4 and mapped to chromosome band Xq24, may consist of as many as 50 variable-length alleles. It represents a class of variable number of tandem repeat polymorphism which may be termed 'macrosatellite'. The cluster is highly methylated on the active X chromosome and hypomethylated on the inactive X.

Absence of linkage of Noonan syndrome to the neurofibromatosis type 1 locus

Eleven families with Noonan syndrome in either two or three generations have been identified. Following the reports of subjects with features of both Noonan syndrome and neurofibromatosis type 1, these pedigrees have been studied using a number of probes at the neurofibromatosis type 1 locus (17q11). A significantly negative lod score was obtained with the intragenic probe NF1-C2, suggesting that the genes for Noonan syndrome and neurofibromatosis type 1 are not contiguous.

Charcot-Marie-Tooth neuropathy related to chromosome 1

One family with documented male-to-male transmission of Charcot-Marie-Tooth (CMT) neuropathy was studied clinically and by genetic linkage. Patients had progressive distal weakness and atrophy, areflexia, and distal sensory loss, but early onset (before age 3 years) in all 5 cases, and phrenic nerve involvement in the propositus (a 39-year-old woman) requiring CPAP ventilator support during the night. Motor-nerve conduction velocities (MNCVs) were significantly slow, consistent with severe demyelinating neuropathy. Electromyography (EMG) data were normal. Two-point and multipoint linkage analyses strongly suggested the presence of a CMT gene on chromosome 1q. A maximum multipoint lod score of 2.70 was obtained at MUC1 (theta = 0), with the locus order centromere-MUC1-SPTA1-Fc gamma RII-AT3-telomere. Multipoint linkage analysis excluded the CMT locus from chromosome 17 markers in this family.

X-linked recessive Charcot-Marie-Tooth neuropathy: clinical and genetic study

We describe three families with X-linked recessive Charcot-Marie-Tooth (CMT) neuropathies. The disease phenotype in family 1 was characterized by infantile onset, weakness of lower legs, areflexia, pes cavus, and mental retardation (2 of 5 patients). The disease phenotype in families 2 and 3 was characterized by late onset, distal weakness, and normal intelligence. Hereditary spastic paraparesis was also present in the CMT patients of family 2. Thirty X-linked DNA markers were used for linkage studies. A maximum lod score of +3.48 was obtained by multipoint linkage analysis for the DXS16 locus mapped at Xp22.2 in family 1. In families 2 and 3, there was suggestion of linkage of Xq26 markers; the peak multipoint lod score for these 2 CMT families was 1.81, at DXS144. These results were suggestive of heterogeneity. The joint analysis including both regions (Xp22.2 and Xq26) provided evidence against homogeneity (chi 2 = 9.12, P less than 0.005).

Two cases of steroid sulfatase deficiency with complex phenotype due to contiguous gene deletions

We report contiguous gene deletions in the distal short arm of the X chromosome in two patients with ichthyosis, due to steroid sulfatase deficiency, and other complex phenotypes. One patient had chondrodysplasia punctata (CDP) and ichthyosis with a normal chromosome constitution. Another patient had a CDP-like phenotype, ichthyosis, and hypogonadism. His karyotype was 46, -X,Y, +der(X)t(X;Y)(p22;q11). DNA from the two patients was analyzed by Southern blotting using cloned fragments mapped in the Xp21-Xpter region to investigate gene deletions. DNA from the patient with CDP showed a gene deletion of the STS, DXS31, and DXS89 loci, and DNA from the patient with X-Y translocation lacked fragments of the STS, DXS31, DXS89, and DXS143 loci. These findings suggest that the common deleted region involving the STS locus might have caused the similar phenotypes in both patients.

Immunohistochemical studies show truncated dystrophins in the myotubes of three fetuses at risk for Duchenne muscular dystrophy

We have performed immunohistochemical studies on muscle tissue of three 12 week old fetuses at risk for DMD, using antisera directed against regions located NH2-proximally and centrally in the rod shaped spectrin-like domain and against the COOH-terminus of dystrophin. All three fetuses had a family history of DMD. Truncated dystrophins were identified in all three cases by a positive reaction with the NH2-proximal antibody, different reactions with the central antibody, and a negative reaction with the COOH-terminal antibody. These data indicate that a panel of antibodies would, in principle, permit 'immunological' mapping of dystrophin mutations. This is diagnostically important in the 35% of families where no mutation is detectable at the DNA level. Secondly, by using this mapping technique it may also become possible to identify the at risk haplotype when DNA analysis is not informative. This may be of great value in DMD carrier detection.

Population variation in molecular polymorphisms of the short arm of the human X chromosome

Five DNA probes (RC8, 754, XJ 1-1, pert 87.8, and L1.28) from the short arm of the human X chromosome were investigated in samples from five populations (English, Nigerian, Chinese, Muslim, and Hindu from India). The variation in the allele frequencies of several probes between different groups was significant. The average heterozygosity in females of the five populations ranged from 32% to 51%. The genetic distance between the five groups was compatible with that using traditional polymorphic systems. There is an interesting suggestion of longitudinal cline for allele *2 (9 kb) detected with probe L1.28. The X-linked RFLPs are useful genetic markers for anthropological studies.

Genetic localisation of the RP2 type of X linked retinitis pigmentosa in a large kindred

Genetic linkage and deletion studies have led to the proposal that there are at least two loci on the X chromosome which are responsible for X linked retinitis pigmentosa (XLRP). One locus (RP3) has been closely defined by genetic linkage and deletion analyses and localised to the region between the ornithine transcarbamylase (OTC) and chronic granulomatous disease (CYBB) loci in Xp21.1-p11.4. The other locus (RP2) has been assigned by linkage analysis alone to region Xp11.4-p11.2, but its localisation is less well defined. The results of a multipoint linkage analysis of a single large XLRP kindred using eight informative loci provide further evidence on the localisation of RP2 to this region. The maximum likelihood location of this locus shows a multipoint lod score of 7.17 close to DXS255 (in Xp11.22) and TIMP (in Xp11.3-p11.23), neither of which show recombination with RP2, in an area extending from 2 cM proximal to DXS7 to 1 cM distal to DXS14 (approximate 95% confidence limits).

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.

Characterization of cDNA clones for the beta subunit of pyruvate dehydrogenase from Ascaris suum

The pyruvate dehydrogenase complex occupies a unique position in the anaerobic mitochondrial metabolism of the parasitic nematode Ascaris suum. This paper describes cDNA clones for the beta subunit of the pyruvate dehydrogenase component of this complex. A cDNA library has been constructed in lambda gt11 from poly(A)+ RNA isolated from adult ascarid body wall muscle. The library was screened with antiserum prepared against the beta subunit of pyruvate dehydrogenase. Full-length clones of 1.2 kb have been characterized. The first 15 amino acids determined from the purified protein match exactly those predicted from the cDNA sequence. The deduced protein sequence contains a 26-amino-acid presequence that has characteristics of mitochondrial targeting sequences. The mature protein is predicted to contain 334 amino acids and is 62% identical to the predicted sequence of the corresponding human subunit. Full-length in vitro transcripts have been translated in vitro to yield a 39-kDa polypeptide consistent with the open reading frame present in the cDNA sequence. The 90 nucleotides at the 3' end of the cDNA sequence have the potential to form a cruciform structure that may play a role in the synthesis of the enzyme.

Localization of DNA sequences to a region within Xp11.21 between incontinentia pigmenti (IP1) X-chromosomal translocation breakpoints

Incontinentia pigmenti (IP) is an X-linked dominant disorder characterized by developmental anomalies of the tissues and organs derived from embryonic ectoderm and neuroectoderm. An IP locus, designated IP1, probably resides in Xp11.21, since five unrelated patients with nonfamilial IP have been identified who possess constitutional de novo reciprocal X;autosome translocations involving Xp11.21. We have used a series of somatic cell hybrids containing the rearranged chromosomes derived from three of the five IP1 patients, along with other hybrid cell lines, to map probes in the vicinity of the IP1 locus. Five anonymous DNA loci--DXS422, DXS14, DXS343, DXS429, and DXS370--have been mapped to a region within Xp11.21, between two IP1 X-chromosomal translocation breakpoints; the IP1 t(X;17) breakpoint is proximal (centromeric) to this region, and the IP1 t(X;13) and t(X;9) X-chromosomal breakpoints lie distal to it. While no IP1 translocation breakpoint has yet been identified by pulsed-field gel electrophoretic (PFGE) analysis, an overlap between three probes--p58-1, 7PSH3.5, and cpX210--has been detected, placing these probes within 125 kb. Four probes--p58-1, 7PSH3.5, cpX210, and 30CE2.8--have been helpful in constructing a 1,250-kb PFGE map of the region between the breakpoints; these results suggest that the IP1 X-chromosomal translocation breakpoints are separated by at least this distance. The combined somatic cell hybrid and PFGE analyses we report here favor the probe order DXS323-(IP1 t(X;13), IP1, t(X;9]-(DXS422, DXS14, DXS343, DXS429, DXS370)-(IP1 t(X;17), DXZ1). These sequences provide a starting point for identifying overlapping genomic sequences that span the IP1 translocation breakpoints; the availability of IP1 translocation breakpoints should now assist the cloning of this locus.

Localization of the microsatellite probe DXS426 between DXS7 and DXS255 on Xp and linkage to X-linked retinitis pigmentosa

The microsatellite marker DXS426 maps to the interval Xp21.1-Xp11.21, the chromosomal region which contains two loci for X-linked retinitis pigmentosa (XLRP; RP2 and RP3). We have refined the localization of DXS426 both physically, by mapping it to a deletion which spans the interval Xp21.3-Xp11.23, and genetically, by studying multiply informative crossovers which indicate that DXS426 lies between DXS7 and DXS255 (i.e., Xp11.4-Xp11.22). As this is the region which contains the RP2 gene, RP2 families could be identified on the basis of linkage of XLRP to DXS426. Multiply informative crossovers in two RP2 families indicate that the most likely location of the RP2 gene is between DXS426 and DXS7. DXS426 is therefore an important highly informative marker for the purposes of carrier detection and early diagnosis of RP2 and for the localization of the disease gene.

Linkage relationship of X-linked juvenile retinoschisis with Xp22.1-p22.3 probes

Linkage analysis was performed to evaluate the relationship between the locus for X-linked juvenile retinoschisis (RS) and five X-chromosomal markers-RC8 (DXS9), SE3.2L (DXS16), 99-6 (DXS41), D2 (DXS43), and 782 (DXS85)-all mapped to the interval Xp22.1-p22.3. Seven U.S. families with 56 affected males were studied. No recombinants were found between RS and DXS9 with a maximum lod score (Z) of 4.93 at a recombination fraction of zero. Obligate recombinants were found for RS with DXS16, DXS41, DXS43, and DXS85. Multipoint linkage analysis and consideration of recombination events within pedigrees suggest that DXS41 and DXS43, and also DXS41 and DXS16, flank RS and that DXS85 lies outside the interval DXS41-DXS43. Our pedigrees provide no evidence for genetic heterogeneity of RS, with five of our families individually showing evidence of linkage. (Z greater than 2.0) to the least one of these probes from Xp22.1-p22.3.

Linkage studies and deletion screening in choroideremia

Fourteen families with choroideremia (TCD) have been examined for linkage to nine genetic markers located on the proximal long arm of the X chromosome. Linkage to three markers (DXYS1, DXS72, DXS3) located in Xq21 was found with a four point lod score of 8.25. No evidence of submicroscopic deletions was observed using DXS233 and DXS232, both thought to lie within about 1 Mb of the TCD gene.

Unusual X chromosome inactivation in a mentally retarded girl with an interstitial deletion Xq27: implications for the fragile X syndrome

A de novo interstitial deletion (X)(q27.1q27.3), between the loci DXS 105 and F8, has been found in a mentally retarded female. The deleted X chromosome is preferentially early replicating in fibroblasts, B cells and T cells, suggesting that the missing region plays a role in inactivation of the X chromosome. None of the available DNA probes except DXS 98 maps to the deleted region of about 10,000 kb. The locus FRAXA is either included in the deletion, or located close to the distal break point.

Genetic counselling in Duchenne and Becker muscular dystrophy is problematic when carrier studies give controversial results

DNA-analysis with flanking and intragenic markers gave confusing results in 7 out of 74 (9.5%) Finnish families with Duchenne or Becker muscular dystrophy. In five families a sister or maternal aunt of the patient had elevated serum creatine kinase (CK) activity, although DNA-analysis indicated a low risk for carriership. In one family the two affected brothers had different pERT87 alleles. In one family the intragenic deletion found in a patient was not present in his mother, who was an obligatory carrier. Deletions were detected with cDNA probes in the probands in five of the families, but the controversy regarding carriership still remained. It is necessary to combine all available data from pedigree analysis, CK measurements, and DNA studies whenever carrier studies are performed, but it appears that major problems in counselling and prenatal diagnosis will still remain in a proportion of the families.

Construction of gene libraries for each human chromosome

We describe the construction of two complete sets of small insert, complete digest DNA libraries for each of the 24 human chromosomal types by the National Laboratory Gene Library Project. Flow sorting was used to purify the chromosomes which provided the DNA for cloning. One set of libraries was cloned into the HindIII site of the lambda vector Charon 21A, and the other set was cloned into the EcoRI site of the same vector. Characterization information from both in-house experiments and user feedback is presented. These chromosome-specific libraries are available to the general scientific community from a repository at the American Type Culture Collection, Rockville, MD. The second phase of the project, the construction of large insert, partial digest libraries in both lambda and cosmid vectors, is underway.

Absence of a single repeat from the coding region of the human involucrin gene leading to RFLP

The human involucrin gene has been mapped to the region q21-q22 of chromosome 1. Three of six Utah families examined were polymorphic for a PstI fragment of the involucrin gene. In one individual, the variant PstI fragment was found by DNA sequencing to be missing one of the 39 repeats that make up two-thirds of the coding region.

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).

Norrie disease gene is distinct from the monoamine oxidase genes

The genes for MAO-A and MAO-B appear to be very close to the Norrie disease gene, on the basis of loss and/or disruption of the MAO genes and activities in atypical Norrie disease patients deleted for the DXS7 locus; linkage among the MAO genes, the Norrie disease gene, and the DXS7 locus; and mapping of all these loci to the chromosomal region Xp11. The present study provides evidence that the MAO genes are not disrupted in "classic" Norrie disease patients. Genomic DNA from these "nondeletion" Norrie disease patients did not show rearrangements at the MAOA or DXS7 loci. Normal levels of MAO-A activities, as well as normal amounts and size of the MAO-A mRNA, were observed in cultured skin fibroblasts from these patients, and MAO-B activity in their platelets was normal. Catecholamine metabolites evaluated in plasma and urine were in the control range. Thus, although some atypical Norrie disease patients lack both MAO-A and MAO-B activities, MAO does not appear to be an etiologic factor in classic Norrie disease.

L2, a DNA fragment from Xq24-q27, detects an EcoR1 RFLP (HGM9 no. DXS12)

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Linkage analysis of a large Latin-American family with X-linked retinitis pigmentosa and metallic sheen in the heterozygote carrier

An extended linkage analysis was performed on the large Latin-American kindred with X-linked retinitis pigmentosa (XLRP) and metallic sheen in the heterozygous carrier studied and reported previously by R.L. Nussbaum et al. (1985, Hum. Genet. 70:45-50) and on a smaller family with the same XLRP variant. In these kindreds the XLRP locus shows close linkage with Xp21 marker loci OTC and DXS206. The results of this linkage analysis agree with the observations made by Nussbaum et al. (1985) that an XLRP locus is distal to DXS7.

Localization of the gene for classic Alport syndrome

The inheritance of Alport syndrome has been controversial for 30 years because no clear diagnostic criteria were established to define a clinically homogeneous group of patients. In this study, 41 families with "classic" Alport syndrome were identified and studied. All the pedigrees are compatible with X-linked inheritance. A formal genetic study confirmed linkage to probe S21 (DXS17), with a maximum LOD score of 4.72 at a recombination frequency of 0.06.

A deletion map of the WAGR region on chromosome 11

The WAGR (Wilms tumor, aniridia, genitourinary anomalies, and mental retardation) region has been assigned to chromosome 11p13 on the basis of overlapping constitutional deletions found in affected individuals. We have utilized 31 DNA probes which map to the WAGR deletion region, together with six reference loci and 13 WAGR-related deletions, to subdivide this area into 16 intervals. Specific intervals have been correlated with phenotypic features, leading to the identification of individual subregions for the aniridia and Wilms tumor loci. Delineation, by specific probes, of multiple intervals above and below the critical region and of five intervals within the overlap area provides a framework map for molecular characterization of WAGR gene loci and of deletion boundary regions.

X-linked dominant Charcot-Marie-Tooth neuropathy with 15 cases in a family genetic linkage study

A large CMT family with 5 affected males and 10 affected females of 37 members in four generations was investigated by recombinant DNA studies. The proband patient in his original description of the pedigree indicated male-to- male transmission in one of his relatives, suggesting autosomal dominant inheritance. The genetic linkage study between the CMT locus and the loci of six markers mapped on chromosome 1 (FY, APCS, AT3, REN, APOA2, and GBA) gave negative results. These findings prompted further pedigree investigation which proved that male-to-male transmission was not present. A genetic linkage study with DXYS1, which is a DNA marker mapped on the long arm of the chromosome X, revealed tight linkage with z = 3.15 at theta = 0.10.

Infantile autism, fragile (X) (q27.3) and RFLP analysis in an extended Swedish family

In an extended family with eight individuals with infantile autism, in association with other developmental disorders and fragile (X) (q27.3), DNA techniques were used to investigate linkage between X chromosomal probes and the disorder. F9 was not informative and recombination was found between fragile X and DXS15, DXS51 and DXS52.

Localization of the gene for X-linked recessive type of retinitis pigmentosa (XLRP) to Xp21 by linkage analysis

The X-linked recessive type of retinitis pigmentosa (XLRP) causes progressive night blindness, visual field constriction, and eventual blindness in affected males by the third or fourth decade of life. The biochemical basis of the disease is unknown, and prenatal diagnosis and definitive carrier diagnosis remain elusive. Heterogeneity in XLRP has been suggested by linkage studies of families affected with XLRP and by phenotypic differences observed in female carriers. Localization of XLRP near Xp11.3 has been suggested by close linkage to an RFLP at the locus DXS7 (Xp11.3) detected by probe L1.28. In other studies a locus for XLRP with metallic sheen has been linked to the ornithine transcarbamylase (OTC) locus mapping to the Xp21 region. In this study, by linkage analysis using seven RFLP markers between Xp21 and Xcen, we examined four families with multiple affected individuals. Close linkage was found between XLRP and polymorphic sites OTC (theta = .06 with lod 5.69), DXS84 (theta = .05 with lod 4.08), and DXS206 (theta = .06 with lod 2.56), defined by probes OTC, 754, and XJ, respectively. The close linkage of OTC, 754, and XJ to XLRP localizes the XLRP locus to the Xp21 region. Data from recombinations in three of four families place the locus above L1.28 and below the Duchenne muscular dystrophy (DMD) gene, consistent with an Xp21 localization. In one family, however, one affected male revealed a crossover between XLRP and all DNA markers, except for the more distal DXS28 (C7), while his brother is recombined for this marker (C7) and not other, more proximal markers. This suggests that in this family the XLRP mutation maps near DXS28 and above the DMD locus.

Human monoamine oxidase gene (MAOA): chromosome position (Xp21-p11) and DNA polymorphism

An essentially full-length cDNA clone for the human enzyme monoamine oxidase type A (MAO-A) has been used to determine the chromosomal location of a gene encoding it. This enzyme is important in the degradative metabolism of biogenic amines throughout the body and is located in the outer mitochondrial membrane of many cell types. Southern blot analysis of PstI-digested human DNA revealed multiple fragments that hybridized to this probe. Using rodent-human somatic cell hybrids containing all or part of the human X chromosome, we have mapped these fragments to the region Xp21-p11. A restriction fragment length polymorphism (RFLP) for this MAOA gene was identified and used to evaluate linkage distances between this locus and several other loci on Xp. The MAOA locus lies between DXS14 and OTC, about 29 cM from the former.

Bkm sequences from the human X chromosome contain large clusters of GATA/GACA repeats

In order to determine whether the regional localizations of Bkm repeats detected on the human X chromosome consisted of typical GATA/GACA repeats, clones were isolated, mapped, and sequenced. Nine Bkm-hybridizing clones from Kunkel's fluorescent-activated, cell-sorted X-chromosome library were all unique. Five were mapped in detail with restriction enzymes and the Bkm-hybridizing segments were localized. Confirmation of X chromosomal homology was obtained for 2 of the clones and Bkm segments from these 2 clones were sequenced. Seventeen contiguous GATA repeats were found in each clone and the overall repeat arrangement showed relatively few differences from previously sequenced Bkm sequences. These are the first sequences of human Bkm repeats. The results, when compared with previously published results, suggest that there may be significant differences between the organization of Bkm repeats on the human X and on the human Y chromosome.

Molecular genetics in muscular dystrophy research: revolutionary progress

The contribution of "reverse genetic" strategies to neuromuscular disease research is evident in the progression of breakthroughs that have recently culminated in the cloning of the Duchenne muscular dystrophy (DMD) cDNA. The resultant improvements in our understanding of the genetic basis of Becker muscular dystrophy (BMD) and DMD serve as models for similar investigation of other heritable disorders. These genetic advances have outpaced concurrent work on the molecular pathogenesis of the dystrophic process, with the curious result that inferences about the DMD protein's amino acid sequence have preceded any information about its function or intracellular localization. In recognition that this foundation sets the stage for the rapid elucidation of the disease's pathogenesis, we review the experimental basis of such advances, with reference to relevant progress in basic myology, pathology, and molecular biology. We conclude with a view towards the ultimate clinical implications of these experimental breakthroughs.