A 2.5-Mb physical map within 3p21.1 spans the breakpoint associated with Greig cephalopolysyndactyly syndrome.

Numerous investigations suggest that one or more genes residing in the p14 to p21 region of human chromosome 3 are critical to the development of neoplastic diseases such as renal cell carcinoma and small-cell lung cancer (SCLC). This region is additionally involved in several interchromosomal translocations, one of which is associated with the developmental disorder Greig cephalopolysyndactyly syndrome. A series of five loci that map in close proximity to the Greig syndrome breakpoint [t(3;7)(p21.1;p13)] at 3p21.1 have been physically linked by pulsed-field gel analysis over a 2.5-Mb region. The probes include ACY1, cA84 (D3S92), cA199 (D3S93), pHF12-32 (D3S2), and MW-Not153 (D3S332). The Greig 3;7 translocation breakpoint was discovered between clones cA199 and MW-Not153, separated by 825 kb. Further analysis revealed comigration of a rearranged fragment detected by MW-Not153 and a chromosome 7 probe previously shown to be in close proximity to the breakpoint (CRI-R944). This latter probe also detects a rearrangement in a second Greig-associated translocation, (6;7)(q27;p13). The physical map resulting from this analysis orders the markers along the chromosome and identifies several locations for CpG islands, likely associated with genes. Although probe pEFD145.1 (D3S32) has been genetically linked to D3S2 (2 cM), physical linkage to the other five loci could not be demonstrated. One of the linked loci, D3S2, has been widely utilized in the analysis of chromosome 3p loss in several malignant diseases. Since expression of ACY1, a housekeeping gene, is specifically reduced in many cases of SCLC, knowledge of its precise chromosomal position and identification of neighboring putative gene loci should facilitate investigation into the mechanism of this reduction.     

Greig syndrome associated with an interstitial deletion of 7p: confirmation of the localization of Greig syndrome to 7p13

Summary An 11-month-old infant with Greig cephalopolysyndactyly syndrome and mild developmental delay is described. High-resolution chromosomal analysis showed a de novo interstitial deletion of chromosome 7p with breakpoints located at p13 and p14. Cytogenetic analysis of polymorphisms of the heterochromatin in the pericentromeric region suggested the deleted chromosome was of paternal origin. This case confirms the localization of Greig syndrome to 7p13 and emphasizes the importance of performing cytogenetic studies on patients with Mendelian disorders who have unusual findings or cognitive abnormalities in a disorder usually associated with normal intellect. Review of clinical features in published reports of patients with a deletion involving 7p13 showed a number to have features overlapping with Greig syndrome. Because of this, we suggest that cytogenetic aberrations, particularly chromosomal microdeletions, may represent a significant etiology for Greig syndrome.     

Localization of genes and anonymous DNA probes on the short arm of Chromosome 7

We have previously described the cytogenetic analysis of two patients with Greig cephalopolysyndactyly syndrome (GCPS) and various microdeletions on the short arm of Chromosome (Chr) 7. Using genes and anonymous DNA probes from 7p we analyzed the DNA of our patients for loss of heterozygosity, or we determined the copy number by semiquantitative Southern hybridization. We have been able to show hemizygosity for the genes of INHBA, IGFBP1 and GLI3 in both patients and therefore can give the chromosomal assignment 7p 12.3-p13. CRI-R944 and CRI-P137 map to the same region, whereas CRI-S207 can be assigned to 7p13-p14.2; TM102L, TS93, TS194, TM77 and TN177 showed no change and these probes map distal to 7p14.2.     

Molecular and cytogenetic analysis in two patients with microdeletions of 7p and Greig syndrome: hemizygosity for PGAM2 and TCRG genes

Greig cephalopolysyndactyly syndrome (GCPS) is an autosomal dominant disorder that has been mapped to 7p13. We have investigated two patients with GCPS and a cytogenetically visible microdeletion of the short arm of chromosome 7 with gene probes that have been assigned close to the proposed Greig locus. Deletion breakpoints were determined from high-resolution G- and R-banded chromosomes. In patient BC with a de novo deletion (7p12.3-7p14.2) we have found a loss of the genomic region containing the T-cell receptor gamma (TCRG) gene cluster, whereas the other patient IR with a deletion (7p11.2-7p13) due to a de novo translocation was apparently normal for this region. Gene dosage analysis revealed a loss of the phosphoglycerate mutase muscular form (PGAM2) gene locus in both patients. Hox 1.4 and interferon-beta 2 (IFNB2) showed a normal gene dosage. Our investigations revealed the following ordering and assignments of the studied genes: PGAM2 and GCPS in 7p12.3-13; TCRG in the distal part of 7p13-7p14.2; Hox 1.4 and IFNB2 distal to 7p14.2. Our results suggest a location of the TCRG gene more proximal than that reported previously. Furthermore, we were able to exclude the Hox 1.4 gene from involvement in the pathogenesis of GCPS.     

Replication of linkage of familial hypobetalipoproteinemia to chromosome 3p in six kindreds

Familial hypobetalipoproteinemia (FHBL) is a genetically heterogeneous condition characterized by very low apolipoprotein B (apoB) concentrations in plasma and/or low levels of LDL-cholesterol (LDL-C) with a propensity to developing fatty liver. In a minority of cases, truncation-specifying mutations of the apoB gene (APOB) are etiologic, but the genetic basis of most cases is unknown. We previously reported linkage of FHBL to a 10 cM region on 3p21.1-22 in one kindred. The objectives of the current study were to identify other FHBL families with linkage to 3p and to narrow the FHBL susceptibility region on 3p. Six additional FHBL kindreds unlinked to the APOB region on chromosome 2 were genotyped with polymorphic markers spanning a region of approximately 13 cM on chromosome 3. Quantitative linkage analyses indicated that the FHBL in these families was linked to 3p21.1-22. Haplotype analysis identified several meiotic crossover events, allowing us to narrow the critical region from 10 cM to 2.0 cM, between markers D3S2407 and D3S1767.     

Susceptibility loci for preeclampsia on chromosomes 2p25 and 9p13 in Finnish families

Preeclampsia is a common, pregnancy-specific disorder characterized by reduced placental perfusion, endothelial dysfunction, elevated blood pressure, and proteinuria. The pathogenesis of this heterogeneous disorder is incompletely understood, but it has a familial component, which suggests that one or more common alleles may act as susceptibility genes. We hypothesized that, in a founder population, the genetic background of preeclampsia might also show reduced heterogeneity, and we have performed a genomewide scan in 15 multiplex families recruited predominantly in the Kainuu province in central eastern Finland. We found two loci that exceeded the threshold for significant linkage: chromosome 2p25, near marker D2S168 (nonparametric linkage [NPL] score 3.77; P=.000761) at 21.70 cM, and 9p13, near marker D9S169 (NPL score 3.74; P=.000821) at 38.90 cM. In addition, there was a locus showing suggestive linkage at chromosome 4q32 between D4S413 and D4S3046 (NPL score 3.13; P=.003238) at 163.00 cM. In the present study the susceptibility locus on chromosome 2p25 is clearly different (21.70 cM) from the locus at 2p12 found in an Icelandic study (94.05 cM) and the locus at 2q23 (144.7 cM) found in an Australian/New Zealand study. The locus at 9p13 has been shown to be a candidate region for type 2 diabetes in two recently published genomewide scans from Finland and China. The regions on chromosomes 2p25 and 9p13 may harbor susceptibility genes for preeclampsia.     

A somatic cell hybrid panel and DNA probes for physical mapping of human chromosome 7p.

To identify by reverse genetics genes on the short arm of human chromosome 7 expected to be involved in the regulation of human craniofacial and limb development, we have set up a human mouse somatic cell hybrid panel that divides 7p into 9 fragments. The breakpoints are defined by deletions or translocations involving one chromosome 7 in the cells of the human cell fusion partners. Particularly densely covered with these cytogenetic anchor points is the proximal area of 7p within and around 7p13. The number of cytogenetic mapping points within proximal 7p could be increased by four, using two diploid human cell lines with small interstitial deletions in this region for dosage studies. We used Southern blots of this panel to assign to 7q or subregions of 7p more than 300 arbitrary DNA probes or genes that provide reference points for physical mapping of 7p. Three reciprocal translocations with one of the breakpoints in 7p13 mark the location of a gene involved in Greig cephalopolysyndactyly syndrome. To define an area in which we could identify candidates for this developmental gene, we established a macrorestriction map using probes flanking the putative gene region. The Greig translocations were found to be located within a 630-kb NotI restriction fragment.     

Association of Treacher Collins syndrome and translocation 6p21.31/16p13.11: exclusion of the locus from these candidate regions.

Treacher Collins syndrome (TCS) is an autosomal dominant defect of craniofacial development which has not been chromosomally localized. We have identified a mother and two children who have TCS and also a balanced translocation t(6;16)(p21.31;p13.11), which suggested the possibility that the TCS locus might be located at one of the translocation breakpoints. These were defined by in-situ hybridization as 6p21.31 (by using loci in the HLA complex defined by the probes p45.1DP beta 003/HLA-DPB2 and pRS5.10/HLA class I chain) and 16p13.11 (by using probes pACHF1.3.2/D16S8 and VK45/D16S131). Pairwise and multipoint linkage analysis using localized chromosome 6 probes and chromosome 16 probes in 12 unrelated TCS families with multiple affected siblings excluded the TCS locus from proximity to both translocation breakpoints. These data were confirmed when a third affected child, who did not exhibit the translocation, was born to the mother.     

A genetic linkage map of 96 loci on the short arm of human chromosome 3.

We constructed a genetic map of 96 loci on the short arm of human chromosome 3 (3p) in 59 families provided by the Centre d'Etude du Polymorphisme Humaine (CEPH). Twenty-nine continuously linked loci were placed on the map with likelihood support of at least 1000:1; one locus, D3S213, was placed on the map with likelihood support of 871:1; D3Z1, an alpha satellite centromeric repeat probe, was placed on the map with likelihood support of 159:1; 65 loci were assigned regional locations. The average heterozygosity of the uniquely ordered markers was 49%. The map extends from 3p26, the terminal band of 3p, to the centromere (from D3S211 to D3Z1). Multipoint linkage analysis indicated that the male, female, and sex-averaged maps extend for 102, 147, and 116 cM, respectively. The mean genetic distance between uniquely ordered loci on the sex-averaged map was 4.0 cM. Probe density was greatest for the region of 3p between D3F15S2e and the telomere. The sex-averaged map contained two intervals greater than 10 cM. Seventeen probes were localized by fluorescence in situ hybridization. The loci described in this report will be useful in building an integrated genetic and physical map of this chromosome.     

A variant of Freeman-Sheldon syndrome maps to 11p15.5-pter.

Distal arthrogryposis type 1 (DA1) and Freeman-Sheldon syndrome (FSS) are the two most common known causes of inherited multiple congenital contractures. We recently have characterized a new disorder (DA2B) with a phenotype intermediate between DA1 and FSS. We report the mapping of a gene that causes DA2B to chromosome 11p15.5-pter. Linkage analysis in a single kindred generated a positive LOD score of 5.31 at theta = 0 with the marker D11S922, and recombinants localize the gene to an approximately 3.5-6.5-cM region between the marker TH and the telomere. Analysis of additional families improves the LOD score to 6.45 at theta = 0 and suggests linkage homogeneity for DA2B.     

Evidence That the Saethre-Chotzen Syndrome Locus Lies between D7S664 and D7S507, by Genetic Analysis and Detection of a Microdeletion in a Patient

The locus for Saethre-Chotzen syndrome, a common autosomal dominant disorder of craniosynostosis and digital anomalies, was previously mapped to chromosome 7p between D7S513 and D7S516. We used linkage and haplotype analyses to narrow the disease locus to an 8-cM region between D7S664 and D7S507. The tightest linkage was to locus D7S664 ( = 7.16, θ = .00). Chromosomes from a Saethre-Chotzen syndrome patient with t(2;7) (p23;p22) were used for in situ hybridization with YAC clones containing D7S664 and D7S507. The D7S664 locus was found to lie distal to the 7p22 breakpoint, and the D7S507 locus was deleted from the translocation chromosomes. These genetic and physical mapping data independently show that the disease locus resides in this interval.     

Regional mapping panel for human chromosome 17: Application to neurofibromatosis type 1

A somatic cell hybrid mapping panel was constructed to localize cloned DNA sequences to any of 15 potentially different regions of human chromosome 17. Relatively high-resolution mapping is possible for 50% of the chromosome length in which 12 breakpoints are distributed over approximately 45 megabases, with an average spacing estimated at 1 breakpoint every 2-7 megabases. This high-resolution capability includes the pericentromeric region of 17 to which von Recklinghausen neurofibromatosis (NF1) has recently been mapped. Using 20 cloned genes and anonymous probes, we have tested the expected order and location of panel breakpoints and confirmed, refined, or corrected the regional assignment of several cloned genes and anonymous probes. Four markers with varying degrees of linkage to NF1 have been physically localized and ordered by the panel: the loosely linked markers myosin heavy chain 2 (25 cM) to p12----13.105 and nerve growth factor receptor (14 cM) to q21.1----q23; the more closely linked pABL10-41 (D17S71, 5 cM) to p11.2; and the tightly linked pHHH202 (D17S33) to q11.2-q12. Thus, physical mapping of linked markers confirms a pericentromeric location of NF1 and, along with other data, suggests the most likely localization is proximal 17q.     

Further refinement of the location for autosomal dominant retinitis pigmentosa on chromosome 7p (RP9).

A form of autosomal dominant retinitis pigmentosa (adRP) mapping to chromosome 7p was recently reported by this laboratory, in a single large family from southeastern England. Further sampling of the family and the use a number of genetic markers from 7p have facilitated the construction of a series of multipoint linkage maps of the region with the most likely disease gene location. From this and haplotype data, the locus can now be placed between the markers D7S484 and D7S526, in an interval estimated to be 1.6-4 cM. Genetic distances between the markers previously reported to be linked to this region and those described in the recent whole-genome poly-CA map were estimated from data in this and other families. These data should assist in the construction of a physical map of the region and will help to identify candidate genes for the 7p adRP locus.     

Cytologically balanced t(2;20) in a two-generation family with alagille syndrome: cytogenetic and molecular studies.

Alagille syndrome is a clinically defined, dominantly inherited disorder affecting the liver, heart, face, eye, and vertebrae. Alagille syndrome has previously been localized to the short arm of chromosome 20, on the basis of reports of a small number of patients with chromosomal deletions of 20p. We undertook a cytogenetic study of patients with Alagille syndrome and identified a family in which a cytologically balanced translocation between chromosomes 2 and 20, 46,XX/XY, t(2;20)(q21.3;p12), is segregating concordantly with the disease. The breakpoint on chromosome 20p in this t(2;20) is consistent with the shortest region of overlap demonstrated in the reported deletion patients. This is the first report of a translocation associated with 20p and Alagille syndrome, and this rearrangement confirms the location of the Alagille disease gene at 20p12. We have established a somatic cell hybrid from a lymphoblastoid cell line from one of the affected individuals that contains the derivative chromosome 20 (20qter-->p12::2q21.3-->qter) but not the derivative chromosome 2, the normal chromosome 2, or the normal chromosome 20. Southern blot and PCR analysis of probes and sequences from 20p have been studied to define the location of the translocation breakpoint. Our results show that the breakpoint lies distal to D20S61 and D20S56 within band 20p12.     

Tourette syndrome in a pedigree with a 7;18 translocation: identification of a YAC spanning the translocation breakpoint at 18q22.3.

Tourette syndrome is a neuropsychiatric disorder characterized by the presence of multiple, involuntary motor and vocal tics. Associated pathologies include attention deficit disorder and obsessive-compulsive disorder (OCD). Extensive linkage analysis based on an autosomal dominant mode of transmission with reduced penetrance has failed to show linkage with polymorphic markers, suggesting either locus heterogeneity or a polygenic origin for Tourette syndrome. An individual diagnosed with Tourette syndrome has been described carrying a constitutional (7;18) chromosome translocation (Comings et al. 1986). Other family members carrying the translocation exhibit features seen in Tourette syndrome including motor tics, vocal tics, and OCD. Since the disruption of specific genes by a chromosomal rearrangement can elicit a particular phenotype, we have undertaken the physical mapping of the 7;18 translocation such that genes mapping at the site of the breakpoint can be identified and evaluated for a possible involvement in Tourette syndrome. Using somatic cell hybrids retaining either the der(7) or the der(18), a more precise localization of the breakpoints on chromosomes 7 and 18 have been determined. Furthermore, physical mapping has identified two YAC clones that span the translocation breakpoint on chromosome 18 as determined by FISH. These YAC clones will be useful for the eventual identification of genes that map to chromosomes 7 and 18 at the site of the translocation.     

Localization of a gene for autosomal dominant Larsen syndrome to chromosome region 3p21.1-14.1 in the proximity of,but distinct from,the COL7A1 locus.

Larsen syndrome (LS) is a skeletal dysplasia (osteochondrodysplasia) in which multiple dislocations of the large joints are the major feature. Nosology in this group of diseases, which constitutes 8% of Mendelian disorders in man, is primarily based on clinical and radiographic features. Hopes for more accurate classification grounds are currently being met by progress in elucidation of underlying genetic defects. We have performed linkage analysis in a large Swedish kindred with autosomal dominant LS and found the gene (LAR1) to be strongly linked to chromosome 3p markers (Zmax = 13.4 at (theta = .00). Recombination analysis indicates that the LAR1 locus is located in a region defined distally by D3S1581 and proximally by D3S1600, which cytogenetically maps to chromosome region 3p21.1-14.1. Linkage and recombination analysis of a COL7A1 PvuII intragenic polymorphism versus LS and chromosome 3 markers indicate that COL7A1 is located close to, but distinct from, the LAR1 locus.     

Cytogenetic and molecular analysis of an unbalanced translocation (X;7) (q28;p15) in a dysmorphic girl

Summary A severely retarded and dysmorphic girl, carrying an unbalanced X/7 translocation with breakpoints at Xq28 and 7p14, was analyzed by cytogenetic, biochemical and molecular techniques. The X/7 translocated chromosome was found to replicate consistently late in the 105 metaphases analyzed. In 83 of these cells, late replication was limited to the X portion of the abnormal chromosome, whereas in 22 cells incomplete spreading into the autosomal fragment was observed. Southern blot and in situ hybridization experiments with probe G80 (locus D7S373) (previously localized to 7p13–15) and G98 (localized to 7p14–15) assigns the former to 7p15 and the latter to 7p14, thus suggesting the order 7ter-G80-G98-cen. The activity of the enzyme phosphoserine phosphatase localized to 7pter p14 was increased. Southern blotting experiments with 19 probes spanning the entire X chromosome demonstrated that the translocated chromosome had lost a portion of Xq28 (locus DXS51) but still retained part of Xq27 (F9 locus). The results confirm that the proband is trisomic for the region 7p15-pter and monosomic for the region Xq28-qter. Comparing her phenotype with those of other cases of partial trisomy or monosomy 7p, we confirm that band 7p21 is probably involved in skull development.     

The breakpoint on 7p in a patient with t(6;7) and craniosynostosis is spanned by a YAC clone containing the D7S503 locus

We previously reported a patient with an apparently balanced t(6;7) translocation and craniosynostosis. We now demonstrate, by fluorescence in situ hybridization, that the yeast artificial chromosome clone 933_e_l from the Centre d'Etude du Polymorphisme Humain library harbouring the D7S503 locus spans the breakpoint on distal 7p. Recent reports have defined a candidate region for a Saethre-Chotzen craniosynostosis locus between the loci D7S513 and D7S516, a region that includes the D7S503 locus. Since the translocation carrier shows only some of the symptoms characteristic for the Saethre-Chotzen syndrome, it remains unresolved whether the gene disrupted by the translocation event is the only one causing craniosynostosis in this chromosomal region.     

Shwachman-Diamond syndrome with exocrine pancreatic dysfunction and bone marrow failure maps to the centromeric region of chromosome 7

Shwachman-Diamond syndrome (SDS) is an autosomal recessive disorder characterized by exocrine pancreatic insufficiency and hematologic and skeletal abnormalities. A genomewide scan of families with SDS was terminated at approximately 50% completion, with the identification of chromosome 7 markers that showed linkage with the disease. Finer mapping revealed significant linkage across a broad interval that included the centromere. The maximum two-point LOD score was 8.7, with D7S473, at a recombination fraction of 0. The maximum multipoint LOD score was 10, in the interval between D7S499 and D7S482 (5.4 cM on the female map and 0 cM on the male map), a region delimited by recombinant events detected in affected children. Evidence from all 15 of the multiplex families analyzed provided support for the linkage, consistent with a single locus for SDS. However, the presence of several different mutations is suggested by the heterogeneity of disease-associated haplotypes in the candidate region.