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The Illumina/solexa system was utilized to map and sequence the breakpoint regions on flow-sorted derivatives chromosomes from three unrelated mentally retarded patients with denovo balanced chromosomal translocations. The implementation of the method would greatly facilitate large-scale breakpoint mapping and gene finding in patients with disease-associated balanced translocations.

Variants in CLCN4, which encodes the chloride/hydrogen ion exchanger CIC-4 prominently expressed in brain, were recently described to cause X-linked intellectual disability and epilepsy. We present detailed phenotypic information on 52 individuals from 16 families with CLCN4-related disorder: 5 affected females and 2 affected males with a de novo variant in CLCN4 (6 individuals previously unreported) and 27 affected males, 3 affected females and 15 asymptomatic female carriers from 9 families with inherited CLCN4 variants (4 families previously unreported). Intellectual disability ranged from borderline to profound. Behavioral and psychiatric disorders were common in both child- and adulthood, and included autistic features, mood disorders, obsessive–compulsive behaviors and hetero- and autoaggression. Epilepsy was common, with severity ranging from epileptic encephalopathy to well-controlled seizures. Several affected individuals showed white matter changes on cerebral neuroimaging and progressive neurological symptoms, including movement disorders and spasticity. Heterozygous females can be as severely affected as males. The variability of symptoms in females is not correlated with the X inactivation pattern studied in their blood. The mutation spectrum includes frameshift, missense and splice site variants and one single-exon deletion. All missense variants were predicted to affect CLCN4’s function based on in silico tools and either segregated with the phenotype in the family or were de novo. Pathogenicity of all previously unreported missense variants was further supported by electrophysiological studies in Xenopus laevis oocytes. We compare CLCN4-related disorder with conditions related to dysfunction of other members of the CLC family.

X-linked intellectual disability (XLID) is a clinically and genetically heterogeneous disorder. During the past two decades in excess of 100 X-chromosome ID genes have been identified. Yet, a large number of families mapping to the X-chromosome remained unresolved suggesting that more XLID genes or loci are yet to be identified. Here, we have investigated 405 unresolved families with XLID. We employed massively parallel sequencing of all X-chromosome exons in the index males. The majority of these males were previously tested negative for copy number variations and for mutations in a subset of known XLID genes by Sanger sequencing. In total, 745 X-chromosomal genes were screened. After stringent filtering, a total of 1297 non-recurrent exonic variants remained for prioritization. Co-segregation analysis of potential clinically relevant changes revealed that 80 families (20%) carried pathogenic variants in established XLID genes. In 19 families, we detected likely causative protein truncating and missense variants in 7 novel and validated XLID genes (CLCN4, CNKSR2, FRMPD4, KLHL15, LAS1L, RLIM and USP27X) and potentially deleterious variants in 2 novel candidate XLID genes (CDK16 and TAF1). We show that the CLCN4 and CNKSR2 variants impair protein functions as indicated by electrophysiological studies and altered differentiation of cultured primary neurons from Clcn4−/−mice or after mRNA knock-down. The newly identified and candidate XLID proteins belong to pathways and networks with established roles in cognitive function and intellectual disability in particular. We suggest that systematic sequencing of all X-chromosomal genes in a cohort of patients with genetic evidence for X-chromosome locus involvement may resolve up to 58% of Fragile X-negative cases.

We report a familial cryptic reciprocal translocation between 4q35 and 10p15 leading to deletion of the terminal long arm of chromosome 4 and duplication of the terminal short arm of chromosome 10 in two family members who both have immunological disturbances and a similar facial appearance. The precise location and extent of the deletion and duplication was determined by fluorescence in situ hybridization (FISH). Furthermore, we investigated the deletion breakpoint of a previously reported patient with 4q34.3‐qter deletion [Van Buggenhout et al. (2004); Am J Med Genet Part A 131A:186–189]. © 2006 Wiley‐Liss, Inc.

To obtain a deeper insight into the genes and gene networks involved in the development of placentopathies, we have assessed global gene expression in three different models of placental hyperplasia caused by interspecies hybridization (IHPD), cloning by nuclear transfer, and mutation of the Esx1 gene, respectively. Comparison of gene expression profiles of approximately 13,000 expressed sequence tags (ESTs) identified specific subsets of genes with changed expression levels in IHPD, cloned, and Esx1 mutant placentas. Of interest, only one gene of known function and one EST of unknown function were found common to all three placentopathies; however, a significant number of ESTs were common to IHPD and cloned placentas. In contrast, only one gene was shared between IHPD and Esx1 mutant, and cloned and Esx1 mutant placentas, respectively. These genes common to different abnormal placental growth genotypes are likely to be important in the occurrence of placentopathy. Developmental Dynamics 230:149–164, 2004. © 2004 Wiley-Liss, Inc.

TBX22 belongs to the T-box family of transcription factors and was originally found in an in silico approach designed to identify new genes on the human Xq12-q21 region. Mutations in TBX22 have been reported in families with X-linked cleft palate and ankyloglossia (CPX), but the underlying pathogenetic mechanism remained unknown. We have identified mouse Tbx22 and analyzed its expression during embryogenesis by reverse transcriptase-polymerase chain reaction and in situ hybridization. In mouse embryos, it is expressed in distinct areas of the head, namely the mesenchyme of the inferior nasal septum, the posterior palatal shelf before fusion, the attachment of the tongue, and mesenchymal cells surrounding the eye anlage. The localization in the tongue frenulum perfectly correlates with the ankyloglossia phenotype in CPX. Furthermore, we identified positionally conserved binding sites for transcription factors, two of which have been implicated previously in palatogenesis (MSX1, PRX2). Developmental Dynamics 226:579–586, 2003. © 2003 Wiley-Liss, Inc.

RhoGEFs play an important role in various signaling cascades and are implicated in human conditions like cancer and mental retardation. A database search combined with screening of a human neuronal teratocarcinoma library identified two novel RhoGEFs, ARHGEF3 and ARHGEF4 (HGMW-approved symbols). The widely expressed ARHGEF3 transcript of 3561 nucleotides encodes a polypeptide of 526 amino acids with homology to NET1. The ARHGEF4 gene generates two transcripts of 3665 and 4000 nucleotides that translate into 720 amino acid residues. Expression of ARHGEF4 is restricted to brain and the encoded protein shows homology to collybistin. FISH analysis of genomic clones mapped ARHGEF3 to 3p13-21 and ARHGEF4 to 2q22.

DXS6673Eis a candidate gene for nonspecific X-linked mental retardation and encodes a novel Zn-finger protein. The ortholog murine gene DXHXS6673Ein XC-D was isolated and characterized. It is ubiquitously expressed in all embryonic stages and adult tissues. Two different transcription start sites exist that result in two major transcripts of 6055 and 5352 nucleotides, each composed of 25 exons. Exon 1A is tissue specific, whereas exon 1B is transcribed constitutively. Both variants are translated into the same 1370-amino-acid protein. Transcripts are subject to alternative splicing at the 5′-end. Some of the isoforms are developmental stage and tissue specific. Among them, one was present only in embryos and adult brain. Sequence analysis demonstrated evolutionary conservation down to the arthropods and defined several conserved protein motifs. Subcellular localization studies with green fluorescent protein as a reporter showed that DXS6673E is predominantly located in the nucleus due to several functional nuclear localization signals. Three distinct protein distribution patterns in COS-7 cells could be identified.

The pufferfish Fugu rubripes has a compact 400-Mb genome that is approximately 7.5 times smaller than the human genome but contains a similar number of genes. Focusing on the distal short arm of the human X chromosome, we have studied the evolutionary conservation of gene orders in Fugu and man. Sequencing of 68 kb of Fugu genomic DNA identified nine genes in the following order: (SCML2)-STK9, XLRS1, PPEF-1, KELCH2, KELCH1, PHKA2, AP19, and U2AF1-RS2. Apart from an evolutionary inversion separating AP19 and U2AF1-RS2 from PHKA2, gene orders are identical in Fugu and man, and all nine human homologs map to the Xp22 band. All Fugu genes were found to be smaller than their human counterparts, but gene structures were mostly identical. These data suggest that genomic sequencing in Fugu is a powerful and economical strategy to predict gene orders in the human genome and to elucidate the structure of human genes.

Disease associated balanced chromosome rearrangements (DBCRs) have been instrumental in the isolation of many disease genes. To facilitate the molecular cytogenetic characterisation of DBCRs, we have generated a set of >1200 non-chimeric, cytogenetically and genetically anchored CEPH YACs, on average one per 3 cM, spaced over the entire human genome. By fluorescence in situ hybridisation (FISH), we have performed a systematic search for YACs spanning translocation breakpoints. Patients with DBCRs and either syndromic or non-syndromic mental retardation (MR) were ascertained through the Mendelian Cytogenetics Network (MCN), a collaborative effort of, at present, 270 cytogenetic laboratories throughout the world. In this pilot study, we have characterised 10 different MR associated chromosome regions delineating candidate regions for MR. Five of these regions are narrowed to breakpoint spanning YACs, three of which are located on chromosomes 13q21, 13q22, and 13q32, respectively, one on chromosome 4p14, and one on 6q25. In two out of six DBCRs, we found cytogenetically cryptic deletions of 3-5 Mb on one or both translocation chromosomes. Thus, cryptic deletions may be an important cause of disease in seemingly balanced chromosome rearrangements that are associated with a disease phenotype. Our region specific FISH probes, which are available to MCN members, can be a powerful tool in clinical cytogenetics and positional cloning.

We report on a family with an X linked neurodegenerative disorder consisting of mental retardation, blindness, convulsions, spasticity, and early death. Neuropathological examination showed mild hypomyelination. By linkage analysis, the underlying genetic defect could be assigned to the pericentromeric region of the X chromosome with a maximum lod score of 3.30 at θ=0.0 for the DXS1204 locus with DXS337 and PGK1P1 as flanking markers.

DNA probe screening of somatic cell hybrids derived from females with X;autosome translocations has enabled us to define eight new breakpoints within the Xq13-q22 region. Together with other X-chromosome rearrangements that have been described earlier, these breakpoints subdivide the Xq21-q22 region into 20 intervals. Our panel refines the physical assignment of 40 probes in the Xq21-q22 segment. Thus, these X-chromosome rearrangements are useful tools for ordering X-linked markers and genes on the proximal long arm of the human X chromosome. Copyright 1993, 1999 Academic Press

Major diagnostic criteria for the Rud syndrome are ichthyosis, hypogonadism, mental retardation, and epilepsy. Two unrelated patients are presented and compared with 28 reported cases.

In a previous study, we have developed a panel of chromosomal rearrangements for the physical mapping of the q13-q21 region of the human X chromosome (Philippe et al., Genomics 17: 147-152, 1993). Here, we report the physical localization of 36 additional polymorphic markers by polymerase chain reaction analysis. The high density of chromosomal breakpoints in Xq21 allows us to map 58 DNA loci in 22 intervals. As a result, this segment of the X chromosome is saturated with approximately three sequence tagged sites per megabase of DNA, which will facilitate the construction of a YAC contig of this region. Copyright 1995, 1999 Academic Press

Abstract: Linkage analysis is described in a family with X-linked mental retardation, ataxia, weakness, floppiness, delayed motor development, absence of deep tendon reflexes, hearing impairment and loss of vision (MIM no. 301835). The disease has a fatal course due to the susceptibility of the patients to infections, especially of the respiratory tract. Clinical signs indicate impairment of the posterior columns, peripheral motor and sensory neurons and the second and eighth cranial nerves and/or their nuclei. The involvement of the posterior columns of the spinal cord is further suggested by the almost complete absence of myelinated fibers therein. We localized the responsible gene(s) to Xq21.33–q24 between DXS1231 and DXS1001 with a maximum lod score of 6.97. The proteolipid protein gene, which codes for two myelin proteins of the central nervous system and is located in this region, was considered as a candidate gene for this disorder. However, no mutations were found in the protein-coding part of this gene.

Hereditary neuropathy with liability to pressure palsies (HNPP) is a disorder of the peripheral nervous system, the cause of which has recently been identified as a deletion on chromosome 17p. The deletion corresponds to the duplication that is commonly observed in patients with hereditary motor and sensory neuropathy type Ia (HMSNIa, 17p11.2–p12). Therefore, the gene for peripheral myelin protein 22 (PMP-22) is a candidate gene for both HMSNIa and HNPP. Here, we show that a similar deletion is present in one family with HNPP but is clearly absent in another family. Affected members of this family carry the expected two copies of the PMP-22 gene and the surrounding region. Furthermore, linkage analyses of this family exclude a large part of 17p, spanning the area deleted in other families with HNPP, as the location for the disease gene. These data strongly argue for the existence of genetic heterogeneity underlying HNPP. Results from two-point linkage analysis with markers on chromosome 1q are inconsistent with a possible involvement of the locus for HMSNIb in the present family.

A series of thirteen different DNA markers was mapped relative to papillary renal cell carcinoma- and synovial sarcoma-associated translocation breakpoints in Xp11.2 using a panel of tumor-derived somatic cell hybrids in conjunction with Southern blot analysis. Our results indicate that the two translocation breakpoints differ from each other and that the chromosomal break in t(X; 1)-positive papillary renal cell carcinoma is located between the markers PFC-TIMP-OATL1-SYP-TFE3 and DXS226-DXS146-DXS255-OATL2-DXS14. In addition, our current breakpoint analysis has resulted in a revision of the regional localization of the proximal Xp marker DXS226.

Employing a modified Goss-Harris irradiation fusion protocol, we have generated a panel of somatic cell hybrids containing various overlapping fragments of the Xcen-Xp11.4 interval. This region of the human X chromosome is known to carry genes for several hereditary eye diseases including retinitis pigmentosa (RP2), congenital stationary night blindness (CSNB-1) and Norrie disease. These hybrid cell lines were employed to isolate 17 new DNA probes by making use of the Alu polymerase chain reaction (PCR) method and subsequent cloning of the PCR products in a plasmid vector. With these probes, we have characterized two previously described microdeletions spanning the Norrie locus; these deletions have enabled us to subdivide the Xp11.4-p11.3 region into three defined intervals.

We have performed linkage analysis with the DNA markers DXS52 and the clotting factor VIII gene (F8C), in several large families with X-linked adrenoleukodystrophy (ALD). The tight linkage to DXS52 could be extended giving a maximal LOD score of 22.5 at 1 cM. F8C was also tightly linked to ALD with a maximal LOD score of 7.8 without recombination. Multipoint linkage analysis with the markers DXS304, DXS52, and F8C indicated that both the gene for ALD and for F8C are distal to DXS52. In four patients with ALD, no major structural rearrangement in the Xqter region was observed; in particular, there were no abnormalities in the vision blindness genes. DNA analysis appeared to be of use in determination of the carrier status of females at risk, for the determination of the origin of the mutation in a particular family, and for prenatal diagnosis.

In order to characterize a previously described submicroscopic deletion encompassing (part of) the choroideremia (tapetochoroidal dystrophy: TCD) gene, we have cloned a 10.5-kb EcoRI fragment from the patient's DNA: this fragment carries the junction between both deletion endpoints (“junction fragment”). The distal portion of this fragment defines a new marker within, or just distal to the TCD gene. This marker has been employed to confirm the diagnosis in several affected family members, and to rule out carriership in a female at risk with conspicuous clinical signs.

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

Ten families with nephrogenic diabetes insipidus (NDI) have been analysed for restriction fragment length polymorphisms (RFLPs). A search for linkage was performed using various chromosome-specific single-copy DNA probes of known regional assignment to the human X chromosome. Close linkage was found between the disease locus and the markers DXS52, DXS15, DXS134 and the F8 gene. This result assigns the NDI gene to the subtelomeric region of the long arm of the X chromosome. The regional localization of the gene by the identification of closely linked markers should have repercussions for genetic counselling and prevention in NDI families.

In a large kindred with X-linked Menkes disease, linkage studies were performed with a restriction fragment length polymorphism (RFLP) that had been found with a cloned hybridisation probe from the proximal short arm of the X chromosome. This RFLP was considered as a potential genetic marker since the Menkes gene seems to be located near the centromere. Moreover, there is circumstantial evidence that in the (para) centric region of the X chromosome cross-overs are relatively rare. Unexpectedly, however, at least two cross-overs were detected in this family which suggests that the DNA sequence employed is of limited use for early diagnosis and carrier detection in this fatal hereditary disorder.

Human Y chromosomes were purified by dual beam flow sorting from a human x Chinese hamster cell line retaining the Y as the only free human chromosome. DNA was extracted from the Y fraction and cloned into ?gtWES.?B vector arms. More than 100 recombinant clones carrying human inserts have been characterised by Benton-Davis plaque screening and Southern blotting or in situ hybridisation. Several repetitive sequences were found to be predominantly located on the Y, whereas the majority also cross-hybridised with autosomal DNA. One repetitive clone gave a specific hybridisation signal with the X and the Y chromosome but not with autosomes. Preliminary evidence indicates that many clones contain single copy as well as repetitive sequences. However, no Y-specific single copy sequence has yet been identified.

Aicardi's syndrome, which is characterized by agenesis of the corpus callosum, specific chorioretinal abnormalities, and defects of vertebrae and ribs, is considered a probable X-linked dominant trait with male lethality. All features of this syndrome were seen in a girl with a de novo balanced X/3 translocation (46,X,t(X;3)(p22;q12)). It is hypothesized that the clinical picture is the consequence of chromosome breakage within the Aicardi locus. Then, unusual X-inactivation patterns in blood and fibroblasts of this patient can be explained by somatic selection against cells with the Aicardi phenotype.

The gene locus for steroid sulfatase, deficiency of which causes X-linked ichthyosis, is assigned to Xp11?Xpter by analysis of 24 man-Chinese hamster somatic cell hybrids. High steroid sulfatase,activity in a hybrid clone having retained only part of Xq is explained by demonstration of an additional late-replicating human X chromosome. This observation confirms previous evidence for noninactivation of the STS locus.

A pedigree is described that includes three cases of periodic hypokalemic paralysis. Apparently, the disease has arisen by de novo mutation in a father of two affected daughters, who, however, is not affected himself. This is unexpected, since in males the disorder is generally inherited as a fully dominant trait. Therefore we propose that these findings result from an early somatic or a half-chromatid mutation.

Blood specimens from a random sample of 981 South African Negroid females were typed electrophoretically inter alia for their G-6-PD phenotypes. The allele frequency for GdB and GdnonB was found to be 0.8126 and 0.1874 respectively. Calculating the number of individuals expected for each phenotypic class, a highly significant deviation from the Hardy-Weinberg equilibrium became manifest, i.e. there was a deficit of 24.6% of heterozygotes and an excess of 12.3% of each of the two classes of homozygotes.

Fabry's disease (angiokeratoma corporis diffusum) can be diagnosed by determination of a-galactosidase activity in single hair roots. A technique has been developed permitting subsequent analysis of enzyme activity and protein content of hair root cells. We have applied this method examining 8 obligatorily heterozygous sisters as well as their 5 daughters and 10 sons. Especially for identification of heterozygotes, the method described proved to be easy and reliable.

We report linkage data on a new large family with non-specific X linked mental retardation (MRX), using 24 polymorphic markers covering the entire X chromosome. We could assign the underlying disease gene, denoted MRX46, to the Xq25-q26 region. MRX46 is tightly linked to the markers DXS8072, HPRT, and DXS294 with a maximum lod score of 5.12 at θ=0. Recombination events were observed with DXS425 in Xq25 and DXS984 at the Xq26-Xq27 boundary, which localises MRX46 to a 20.9 cM (12 Mb) interval. Several X linked mental retardation syndromes have been mapped to the same region of the X chromosome. In addition, the localisation of two MRX genes, MRX27 and MRX35, partially overlaps with the linkage interval obtained for MRX46. Although an extension of the linkage analysis for MRX35 showed only a minimal overlap with MRX46, it cannot be excluded that the same gene is involved in several of these MRX disorders. On the other hand, given the considerable genetic heterogeneity in MRX, one should be extremely cautious in using interfamilial linkage data to narrow down the localisation of MRX genes. Therefore, unless the underlying gene(s) is characterised by the analysis of candidate genes, MRX46 can be considered a new independent MRX locus.

We identified a large kindred that shows classical myotonic dystrophy (MyD), together with hereditary motor and sensory neuropathy (HMSN) in some individuals, and HMSN alone in others. A previous study of this family has shown cosegregation of the MyD and HMSN phenotypes with the Lutheran and secretor loci in some branches of the family, indicating linkage to chromosome 19. We reanalyzed this family with 2 recombinant DNA marker systems from the ApoC2 locus on chromosome 19. Our results demonstrate that all affected individuals have inherited a unique ApoC2 haplotype that was not found in their clinically and electrophysiologically normal sibs. We also obtained evidence against involvement of the HMSN I locus on chromosome 17. In this family, a moderately severe neuropathy may be the only clinical sign of MyD for many years. Our results are consistent with an unusual neuropathic mutation at the MyD gene. However, involvement of 2 closely linked genes (1 for MyD and the other for HMSN) can also explain our findings.

Autosomal dominant ichthyosis vulgaris and X-linked recessive ichthyosis segregated in three generations of a family and was studied clinically, histologically, and biochemically. Determination of stereoid sulfatase activity ascertained the diagnosis of X-linked recessive ichthyosis and allowed detection of heterozygous carriers.

Fibroblasts of patients with Tay-Sachs' and Sandhoff's disease have been fused. After 7 to 22 days in culture hexosaminidase A-activity could be demonstrated in the hybrid cells both electrophoretically and by heat inactivation.

We have constructed a somatic cell hybrid line, designated 908K1, with a single human der(19) chromosome on a Chinese hamster background by employing conventional as well as microcell-mediated cell fusion techniques. The der(19) chromosome comprises the 19p13.1→q13.2 segment, as well as the distal (Xq24→qter) portion of the X chromosome long arm, and is stably retained by HAT selection. Extensive characterization of this hybrid line and comparison with other somatic cell hybrids has enabled us to regionally assign PGK2 to the distal short arm of chromosome 19 and to narrow down the assignments of CYP1, TGFB, and ERCC1 on 19q. Moreover, a cosmid library has been constructed from this microcell hybrid. By screening this library, as well as a chromosome 19-enriched library obtained elsewhere, 14 single-copy probes have been isolated that map on the 19p13.1→q13.2 segment, and 5 probes were assigned to the distal Xq. It is anticipated that these probes will be useful for the diagnosis of myotonic dystrophy and fra(X) mental retardation.

Choroideremia (tapeto-choroidal dystrophy, TCD), an X chromosome-linked disorder of retina and choroid, causes progressive nightblindness and central blindness in affected males by the third to fourth decade of life. Recently, we have been able to map the TCD gene to a small region of overlap between five different, male-viable Xq21 deletions that were found in patients with TCD and other clinical features. Two families were identified in which classical, nonsyndromic TCD is associated with small interstitial deletions that are only detectable with probe p1bD5 (DXS165). To characterize these and two other deletions that were identified more recently, we have used the chromosome walking and jumping techniques to generate a set of five chromosomal-jumping clones flanking the DXS165 locus at various distances. With these clones, we could localize four of the eight deletion endpoints and the breakpoint on the X chromosome of a female with a de novo X/13 translocation and choroideremia. These studies assign the TCD gene, or part of it, to a DNA segment of only 15-20 kilobases.

We have generated a human subtelomere probe panel, utilizing well characterized CEPH YACs, for the investigation of human chromosome pathology and evolution through fluorescent in situ hybridization (FISH). Region-specific FISH probes will be extremely valuable for detecting cytogenetically cryptic telomere abnormalities. Here, we present the first comparative mapping study (with 29 subtelomere probes and 6 chromosome paints) to the Old World monkey Presbytis cristαtα, followed by hybridizations to the great apes, gorilla and orangutan, when rearrangements were detected. We observed that the position of telomere-associated genomic sequences has been only moderately conserved during primate evolution. YAC 364f9, specific for the subtelomeric long arm of human chromosome 3, contains an evolutionary inversion breakpoint that was involved in independent chromosome rearrangements in P. cristαtα and gorilla.

Hybridization studies using a panel of somatic cell hybrids with subchromosomal segments of 19q have localized the genes encoding hormone-sensitive lipase (LIPE), carcinoembryonic antigen (CEA), and small nuclear ribonucleoprotein polypeptide A (SNRPA) to various regions of 19q13.1; the cellular receptor for poliovirus sensitivity (PVS) to 19ql3.2; and the genes coding for prostate-specific antigen (APS), human pancreatic kallikrein (KLK1), and small nuclear ribonucleoprotein 70-kD poly-peptide (SNRP70) to 19q 13.3 →qter. Our results exclude several of these genes from being seriously considered as a candidate for the myotonic dystrophy gene on 19q.

In order to elucidate the cellular and molecular processes which are involved in Norrie disease (ND), we have used gene targeting technology to generate ND mutant mice. The murine homologue of the ND gene was cloned and shown to encode a polypeptide that shares 94% of the amino acid sequence with its human counterpart. RNA in situ hybridization revealed expression in retina, brain and the olfactory bulb and epithelium of 2 week old mice. Hemizygous mice carrying a replacement mutation in exon 2 of the ND gene developed retrolental structures in the vitreous body and showed an overall disorganization of the retinal ganglion cell layer. The outer plexiform layer disappears occasionally, resulting in a juxtaposed inner and outer nuclear layer. At the same regions, the outer segments of the photoreceptor cell layer are no longer present. These ocular findings are consistent with observations in ND patients and the generated mouse line provides a faithful model for study of early pathogenic events in this severe X-linked recessive neurological disorder.

The mammalian sex chromosomes are thought to be related to each other by sharing a common origin. That is, the X and Y chromosomes originally evolved from a pair of chromosomes that only differed at the locus determining sexual differentiation1,2. For example, this evolutionary relationship is reflected during meiosis3in chromosomal pairing between the tip of the human X chromosome short arm and the Y chromosome which presumably implies sequence homology4. However, compelling genetic evidence for functional homology between the mammalian X and Y chromosome is lacking. We describe here the localization of a gene to the tip of the short arm of the human X chromosome and evidence for a related gene on the Y chromosome.

Autosomal, dominantly inherited, non-chromaffin paragangliomas are tumors of the head and neck region occurring with a frequency of 1:30 000. Genomic imprinting probably influences the expression of the disorder, because tumor development is limited to individuals who have inherited the trait from their father. By linkage analysis and haplotyping of a single large family in which the pattern of inheritance is consistent with genomic imprinting, we have mapped the gene to a 5 cM region of chromosome 11q13.1 between D11S956 and PYGM. A maximum lod score of 7.62 at T = 0.0 was obtained for D11S480. This interval does not overlap with a recently assigned locus for glomus tumors in other families: 11q22.3-q23.3. Furthermore, analysis of a second family showing the imprinting phenomenon resulted in the exclusion of the 5 cM area as the location of the disease gene, whereas an indication for linkage was obtained (Z = +2.65) with markers from the distal locus. These observations argue for the presence of two distinct imprinted genes for glomus tumors on 11q. A model for tumor initiation and progression is presented based on all available information.

The gene for autosomal, dominantly inherited, non-chromaffin paragangliomas has previously been mapped at 11q23-qter by linkage analysis of a single family. In the present study, we have used genetic markers from 11q for the analysis of two distantly related pedigrees with the same disorder. Linkage analysis and haplotyping indicate that the gene underlying the disorder in the present family is located on chromosome 11q proximal to the tyrosinase gene locus (11q14–q21). Closely linked markers are the human homologue of the murine INT2 protooncogene and the anonymous DNA marker D11S527. A maximum lod score of 5.4 (?=0.0) has been obtained for linkage between the disorder and the chromosomal region defined by these markers. The human INT2 gene can be regarded as a candidate for the disorder on the basis of its expression pattern during embryogenesis in the mouse. However, haplotype analysis indicates that this gene is probably not the predisposing genetic factor in the present family.

Linkage studies and cytogenetically visible deletions associated with nonspecific X-linked mental retardation (XLMR) and a specific form of deafness (DFN3) have indicated that the genes responsible for these disorders are located at Xq21. Using DNA probes from this region, we have studied several overlapping deletions spanning different parts of Xq21. This has enabled us to assign the DFN3 gene and a gene for nonspecific XLMR to an interval that encompasses the locus DXS232 and that is flanked by DXS26 and DXS121.

Norrie disease (ND), atrophia bulborum hereditaria, is caused by a gene defect on the proximal short arm of the X-chromosome. As shown by us and others, microdeletions spanning the DXS7 locus are not uncommon in this disorder, and there is recent evidence that, at least in some of the Norrie deletion patients, the monoamine oxidase (MAO) A and B genes are deleted as well. Molecular hybridization experiments with 19 cloned DNA fragments have enabled us to construct a preliminary long-range restriction map around DXS77, DXS7, MAO-A and MAO-B, and to localize the distal end point of an ND deletion between DXS77 and DXS7.