Characterisation of interstitial duplications and triplications of chromosome 15q11–q13

Chromosome 15 is frequently involved in the formation of structural rearrangements. We report the molecular characterisation of 16 independent interstitial duplications, including those of one individual who carried a duplication on both of her chromosomes 15, and three interstitial triplications of the Prader-Willi/Angelman syndrome critical region (PWACR). In all probands except one, the rearrangement was maternal in origin. In one family, the duplication was paternal in origin, yet appeared to segregate in a sibship of three with an abnormal phenotype that included developmental delay and a behavioural disorder. Ten duplications were familial, five de novo and one unknown. All 16 duplications, including two not visible by routine G-banding, were of an almost uniform size and shared the common deletion breakpoints of Prader-Willi syndrome and Angelman syndrome. Like deletions, the formation of duplications can occur in both male and female meiosis and involve both inter- and intrachromosomal events. This implies that at least some deletions and duplications are the reciprocal products of each other. We observed no instances of meiotic instability in the transmission of a duplication, although recombination within the PWACR occurred in two members of the same family between the normal and the duplicated chromosome 15 homologues. All three triplications arose de novo and included alleles from both maternal chromosomes 15. Triplication breakpoints were more variable and extended distally beyond the PWACR. The molecular characteristics of duplications and triplications suggest that they are formed by different mechanisms.     

Mosaic loss of 15q11q13 in a patient with hypomelanosis of Ito: is there a role for the P gene?

We report a patient with mental retardation, behavioral disturbances, and pigmentary anomalies, consistent with the phenotype of hypomelanosis of Ito (HMI), and in whom cytogenetic analysis revealed mosaicism for an unbalanced translocation. His karyotype is 45, XY,–7, –15,+der(7)(7;15)t(q34;ql3)/46, XY. He is therefore monosomic for 7q34 to qter and 15pter to q13 in the cells containing the translocation. The human homolog (P) of the p gene (the product of the mouse pink-eyed dilution locus) maps to 15q11q13. Loss of this locus is believed to be associated with abnormalities of pigmentation, such as the hypopigmentation seen in patients with deletions of 15q11q13, and the Prader-Willi and Angelman syndromes. Mutations within the P gene have also been associated with tyrosinase-positive (type II) oculocutaneous albinism. Using fluorescence in situ hybridization, we confirmed that our patient is deleted for one copy of a P gene probe in the cells with the unbalanced translocation, and for loci within the region critical for the Prader-Willi/Angelman syndromes. Although hypomelanosis of Ito is a heterogeneous disorder, we postulate that, in our case and potentially in others, this phenotype may result directly from the loss of specific pigmentation genes.     

Regional assignment of the human C1-inhibitor gene to 11q11–q13.1

Summary In situ hybridisation using a biotinylated 1.8kb human cDNA clone in both normal and structurally abnormal chromosomes supports regional localisation of the gene for human C1-inhibitor to chromosome 11q11-q13.11.     

VEGF: a modifier of the del22q11 (DiGeorge) syndrome?

Hemizygous deletion of chromosome 22q11 (del22q11) causes thymic, parathyroid, craniofacial and life-threatening cardiovascular birth defects in 1 in 4,000 infants. The del22q11 syndrome is likely caused by haploinsufficiency of TBX1, but its variable expressivity indicates the involvement of additional modifiers. Here, we report that absence of the Vegf164 isoform caused birth defects in mice, reminiscent of those found in del22q11 patients. The close correlation of birth and vascular defects indicated that vascular dysgenesis may pathogenetically contribute to the birth defects. Vegf interacted with Tbx1, as Tbx1 expression was reduced in Vegf164-deficient embryos and knocked-down vegf levels enhanced the pharyngeal arch artery defects induced by tbx1 knockdown in zebrafish. Moreover, initial evidence suggested that a VEGF promoter haplotype was associated with an increased risk for cardiovascular birth defects in del22q11 individuals. These genetic data in mouse, fish and human indicate that VEGF is a modifier of cardiovascular birth defects in the del22q11 syndrome.     

Localization of the human c-kit protooncogene on the q11–q12 region of chromosome 4

Summary Using a 166-nucleotide-long DNA synthetic probe corresponding to the v-kit sequence (1458-1623), we have mapped the human c-kit gene to chromosome 4 at the q11–q12 band by in situ hybridization on chromosomes from human lymphocyte preparations.     

The association of a lymphoreticular malignancy with an 11q deletion: A coincidence or a cancer susceptibility?

A balanced paternal chromosome insertion, ins(11) p14q14q21, resulted in a female with an unbalanced karyotype, del(11)(q14q21). This imbalance presumably arose from a meiotic crossover between the breakpoint of the insertion and the breakpoints of the deletion. This child developed a malignant lymphoma of the thymus in the first year of life. The association of a lymphoma with an 11q deletion may not be a coincidence in view of the frequent involvement of 11q in cytogenetic alterations of lymphomas.     

Subregional physical mapping of an αB-crystallin sequence and of a new expressed sequence D11S877E to human 11q

We report the regional assignment on Chromosome (Chr) 11q of two cDNA clones selected as sequences expressed in mature kidney and not expressed in Wilms' tumor. Clone T70 was identified as an B-crystallin sequence (CRYA2). CRYA2 has previously been mapped to 11q22.3–23.1 by in situ hybridization. Clone 6.2 represents a new gene expressed in adult and fetal kidney, pancreas, and liver. In order to map sequences corresponding to clone 6.2 and to physically define the boundaries of the localization of CRYA2, we used somatic cell hybrids carrying either different human chromosomes or Chr 11 segments and a cell line established from a patient with an interstitial deletion of region 11q14.3–q22.1. We showed that CRYA2 lies proximal to the 11q23.2 breakpoint defined by the constitutional t(11;22) and distal to the 11q22.1 breakpoint (between D11S388 and D11S35) of a constitutional interstitial deletion. This is in agreement with previous data obtained by in situ hybridization and provides proximal and distal physical benchmarks for this localization. Clone 6.2-related sequence (D11S877E) was assigned to region 11q23.2–q24.2 defined by the breakpoints of the constitutional t(11;22) and of the Ewing's sarcoma neuroepithelioma t(11;22).     

Transposition of 9q34 and 22 (q11→qter) regions has a specific role in chronic myelocytic leukemia

Summary Six cases are reported of variant Ph translocations found among 240 patients with Ph-positive CML. Five cases had a three-chromosome rearrangement involving, in addition to chromosomes 9 and 22, chromosomes 7, 4, 2(two), and 3 respectively, and one case had a two-chromosome rearrangement 22/5. A review of the literature revealed that three- and two-chromosome variant Ph translocations are observed with equal frequency. It is postulated that all variant translocations are indeed three-chromosome rearrangements, that the specific event for the formation of the Ph chromosome is the reciprocal translocation 9/22, and that the transposition of regions 9q34 and 22 (q11qter), plays a major role in the development of CML.     

Localization of the human progesterone receptor gene to chromosome 11q22–q23

Summary The human progesterone receptor gene was mapped by in situ hybridization using two cDNA probes corresponding to the 5′ and 3′ part of the coding sequence. This gene was localized to 11q22-q23.     

Molecular characterization of a patient with del(1)(q23–q25)

Summary We report a patient (S.T.) with multiple congenital anomalies and developmental delay associated with an interstitial deletion of 1q23–1q25. Molecular analysis of the deletion was performed using DNA markers that map to 1q. Five DNA markers, MLAJ-1 (D1S61), CRI-L1054 (D1S42), HBI40 (D1S66), OS-6 (D1S75), and BH516 (D1S110), were demonstrated to be deleted. Informative polymorphisms demonstrated this to be a de novo deletion of the maternally derived chromosome. Deletion status was determined using restriction fragment length polymorphism (RFLP) analysis supplemented with densitometry in the experiments where RFLP analysis was not fully informative. Deletions were confirmed by Southern analysis using genomic DNA from a somatic cell hybrid retaining the del(1)(q23–q25) chromosome that was constructed from patient S.T. Flow karyotyping confirmed the deletion and estimated that the deletion encompassed 11,000–16,000 kb. The clinical and cytogenetic characteristics of S.T. are compared with those of ten previously described patients with monosomy 1q21–1q25.     

Haplotypes within genes of β-chemokines in 17q11 are associated with multiple sclerosis: a second phase study

We previously defined haplotypes of single nucleotide polymorphisms (SNP) with possible relevance to multiple sclerosis (MS) in 2 CC chemokine ligand (CCL) clusters in chromosome 17q11. The 17q11 region was also identified as a susceptibility locus by a meta-analysis of linkage studies. To confirm and refine the previous finding in a second, high resolution SNP scan in a new set of families. We genotyped 232 SNPs in 1369 individuals in 361 MS families. Transmission of marker alleles and haplotypes from unaffected parents to affected offspring was tested by using the pedigree disequilibrium test, the TRANSMIT 2.5 program, and the family and haplotype based association tests. Distribution of linkage disequilibrium (LD) was assessed by ldmax. In consensus with observations in the first scan, the present study identified haplotypes within CCL3 and CCL15 in the telomeric CCL cluster. There was also an overlap in the findings in the centromeric CCL cluster. Strong and extensive LD was detected both within the centromeric and telomeric CCL gene clusters. The present study replicates our previous findings and further suggests the existence of MS associated haplotypes within genes of CCL3 and CCL15. Haplotypes of interest are also present within the centromeric gene cluster (including CCL2, CCL7, CCL11, CCL8, and CCL13), but extensive LD prevents further refinement of these haplotypes by using the methods applied. Sequencing of the identified chromosomal segments and their flanking regions will be necessary to define specific variants with direct relevance to MS pathogenesis.     

UV light activates a Gαq/11-coupled phototransduction pathway in human melanocytes

While short exposure to solar ultraviolet radiation (UVR) can elicit increased skin pigmentation, a protective response mediated by epidermal melanocytes, chronic exposure can lead to skin cancer and photoaging. However, the molecular mechanisms that allow human skin to detect and respond to UVR remain incompletely understood. UVR stimulates a retinal-dependent signaling cascade in human melanocytes that requires GTP hydrolysis and phospholipase C β (PLCβ) activity. This pathway involves the activation of transient receptor potential A1 (TRPA1) ion channels, an increase in intracellular Ca²⁺, and an increase in cellular melanin content. Here, we investigated the identity of the G protein and downstream elements of the signaling cascade and found that UVR phototransduction is Gα_q/11 dependent. Activation of Gα_q/11/PLCβ signaling leads to hydrolysis of phosphatidylinositol (4,5)-bisphosphate (PIP₂) to generate diacylglycerol (DAG) and inositol 1, 4, 5-trisphosphate (IP₃). We found that PIP₂ regulated TRPA1-mediated photocurrents, and IP₃ stimulated intracellular Ca²⁺ release. The UVR-elicited Ca²⁺ response appears to involve both IP₃-mediated release from intracellular stores and Ca²⁺ influx through TRPA1 channels, showing the fast rising phase of the former and the slow decay of the latter. We propose that melanocytes use a UVR phototransduction mechanism that involves the activation of a Gα_q/11-dependent phosphoinositide cascade, and resembles light phototransduction cascades of the eye.     

A physical map of large segments of pig Chromosome 7q11–q14: comparative analysis with human Chromosome 6p21

The aim of this study was to establish a porcine physical map along the chromosome SSC7q by construction of BAC contigs between microsatellites Sw1409 and S0102. The SLA class II contig, located on SSC7q, was lengthened. Four major BAC contigs and 10 short contigs span a region equivalent to 800 cR measured by IMpRH7000 mapping. The BAC contigs were initiated by PCR screening with primers derived from human orthologous segments, extended by chromosome walking, and controlled and oriented by RH mapping with the two available panels, IMpRH7000Rad and IMNpRH12000Rad. The location of 43 genes was revealed by sequenced segments, either from BAC ends or PCR products from BAC clones. The 220 BAC end sequences (BES) were also used to analyze the different marks of evolution. Comparative mapping analysis between pigs and humans demonstrated that the gene organization on HSA6p21 and on SSC7p11 and q11-q14 segments was conserved during evolution, with the exception of long fragments of HSA6p12 which shuffled and spliced the SLA extended class II region. Additional punctual variations (unique gene insertion/deletion) were observed, even within conserved segments, revealing the evolutionary complexity of this region. In addition, 18 new polymorphic microsatellites have been selected in order to cover the entire SSC7p11-q14 region.     

人类基因组17q11—q12：癌基因与抗癌基因富集区

由于人基因组１７ｑ１１－ｑ１２含有许多与癌发生有关的基因,因此成了人们研究的热点。本仅就该区域的基因克隆、基因组制图以及这些基因与癌发生的关系作一详细介绍。     

Possible trisomy 1q25→1q32 in a malformed girl with a de novo insertion in 1q

Summary A newborn female is described who exhibited a characteristic facial dysmorphology including deep-set eyes, broad nasal bridge, small mouth, higharched and narrow palate, severely receding mandible and misshapen ears; constant flexion of the proximal interphalangeal joints, and short distal phalanges and nails of fingers; a congenital heart defect; marked muscular hypotonia, motor and growth retardation. She died at 4 months of age. Her karyotype revealed an additional band in 1q. Banding patterns and clinical picture suggest duplication of the segment 1q251q32.     

Maternal origin of deletion 15q11–13 in 25/25 cases of Angelman syndrome

Summary About half of the cases of Angelman syndrome arise from deletions of chromosome band 15q12. In 25 cases we have been able to determine the parental origin of the deletion and, in line with other reported cases, we have found the deletion to be of maternal origin. There were no exceptions. The parental origin was determined using cytogenetic markers in 13 of the cases, in nine by using the pattern of inheritance of restriction fragment length polymorphisms, and in three using both techniques.     

Regional assignment of the gene coding for a human Graves' disease autoantigen to 10q21.3–q22.1

A cDNA coding for a human Graves' disease autoantigen (hGT) has been isolated from a thyroid expression library. Using this cDNA as a probe, the gene for hGT, previously assigned to chromosome 10, has been further localized to 10q21.3–q22.1 by non-isotopic in situ hybridization.     

Localization of a novel locus for alopecia with mental retardation syndrome to chromosome 3q26.33–q27.3

Alopecia with mental retardation syndrome is a rare autosomal recessive disorder characterized clinically by total or partial alopecia and mental retardation. In an effort to understand the molecular bases of this form of alopecia syndrome, large Pakistani consanguineous kindred with multiple affected individuals has been ascertained from a remote region in Pakistan. Genome wide scan mapped the disease locus on chromosome 3q26.33–q27.3. A maximum two-point LOD score of 3.05 (θ=0.0) was obtained at marker D3S3583. Maximum multipoint LOD score exceeding 5.0, obtained with several markers, supported the linkage. Recombination events observed in affected individuals localized the disease locus between markers D3S1232 and D3S2436, spanning 11.49-cM region on chromosome 3q26.33–q27.3. Sequence analysis of a candidate gene ETS variant gene 5 from DNA samples of two affected individuals of the family revealed no mutation.     

Serial duplication of 10 (q21→q22) in a mentally retarded boy with congenital malformations

Summary A boy with congenital malformations and a serial duplication of 10(q21q22) is reported. His clinical picture is compared with that of a previously reported patient with a similar karyotype.