Ring chromosome 22 and neurofibromatosis

Variable constitutional mosaicism, mos45,XY,-22/46,XY,-22,+mar/46,XY,-22,+r(22)/47,XY,-22,+r(22)+mar/ 47, XY,-22,+r(22)*2, was found in PHA-stimulated peripheral blood, in a lymphoblastoid cell line and in cultured skin fibroblasts from a mentally retarded patient with neurofibromatosis. Both the ring chromosome and the small extra marker chromosome stained positively by in situ hybridization with a chromosome 14/22-specific alphoid repeat probe. DNA dosage analysis showed constitutional loss of one copy of the arylsulfatase A gene (ARSA), consistent with its terminal location on 22q. There was no evidence of constitutional loss of D22S1 or D22S28 which flank the neurofibromatosis type 2 (NF2) locus. Analysis of two DNA samples from a skin neurofibroma indicated retainment of two copies of D22S1, whereas the results were ambiguous with respect to tumor-specific loss of one copy of D22S28. It is suggested that the development of neurofibromatosis of unclear type in two r(22) carriers might be associated with somatic mutation of the NF2 locus due to instability of the ring chromosome(s), and in analogy, that somatic mutation of either NF1 or NF2 may account for some cases of neurofibromatosis which do not meet the criteria of either NF1 or NF2. The occurrence of seminoma in the proband may be fortuitous, but could also be due to the presence of a seminoma-associated locus on chromosome 22.     

Constitutional DNA-level aberrations in chromosome 22 in a patient with multiple meningiomas

We describe a patient who developed multiple meningiomas but had no clear evidence of neurofibromatosis type 2. Four of the tumors, derived from three different sites, were analyzed cytogenetically and/or at the DNA level using chromosome 22 specific probes. All four tumors showed loss of the same copy of chromosome 22. On the chromosome that was retained in the tumors, we found two constitutional aberrations, a 1.5 kb deletion and a point mutation. The patient had inherited both alterations from her father. The father has not developed any meningiomas so far but he has been treated for a well-differentiated adenocarcinoma of the lung and a brain metastasis from this tumor. The mother and 75 unrelated individuals did not show any of the chromosome 22 alterations. The multiple tumors found in the patient suggest that she has a predisposing gene for the development of meningiomas. The finding that all investigated tumors lost the same, constitutionally normal copy of chromosome 22 could indicate that the predisposing gene resides on chromosome 22 and was affected by the constitutional mutations. Genes Chrom Cancer 9:124-128 (1994).© 1994 Wiley-Liss, Inc.     

Large genome rearrangements as a primary cause of aging

In his introductory chapter of the Mutation Research special issue on 'Genetic Instability and Aging', the late Bernard Strehler provided some historical perspectives on the long-standing hypothesis that aging is primarily caused by changes in the genome of somatic cells (Strehler, 1995, Mutat. Res. 338 (1995) 3). Based on his own findings of a loss of ribosomal RNA gene copies in postmitotic tissues of dogs as well as humans during aging, his main conclusion was that deletional mutations are more likely than point mutations to be a main causal factor in aging. To directly assess the levels of different types of spontaneous mutations in organs and tissues during aging, we have used a mouse model harboring a chromosomally integrated cluster of lacZ-containing plasmids that can be recovered and analyzed in Escherichia coli. Our results indicate the accumulation of mutations in some but not all organs of the mouse with significant differences in mutational spectra. In addition to point mutations, genome rearrangements involving up to 66 Mb of genomic DNA appeared to be a major component of the mutational spectra. Physical characterization of the breakpoints of such rearrangements indicated their possible origin by erroneous, non-homologous DNA double-strand break repair. Based on their increased occurrence during aging in some tissues and their often very large size, we have designed a model for an aging tissue in terms of a cellular mosaic with a gradual increase in genome rearrangements that leads to functional senescence, neoplastic transformation or death of individual cells by disrupting nuclear architecture and patterns of gene regulation.     

Complex chromosome 22 rearrangements in astrocytic tumors identified using microsatellite and chromosome 22 tile path array analysis

Many studies have reported chromosome 22 as being abnormal in astrocytic tumors. In an attempt to map precisely the abnormal region or regions that potentially harbor tumor-suppressor genes or oncogenes, we constructed a chromosome 22 tile path array covering 82% of 22q with the use of 441 chromosome 22 clones. A 10-Mb whole-genome array consisting of 270 clones from all autosomes was included in the array. A total of 126 astrocytic tumors-5 diffuse astrocytomas (A), 29 anaplastic astrocytomas (AA), and 92 glioblastomas (GB)-were examined for chromosome 22 alterations both by microsatellite analysis (using 28 markers to identify allelic imbalance) and with the tile path array. The results showed that chromosome 22 alterations in astrocytic tumors could be complex. A number of tumors had a combination of deletions with and without reduplication of the retained chromosome, as well as copy number gains and amplifications. In two glioblastomas, overlapping homozygous deletions were identified that involved three genes (DEPDC5/KIAA0645, YWHAH, C22ORF24/HSN44A4A). The terminal region telomeric to the clone RP3-398C22 appeared to be the most frequently deleted region. The estimated incidence of any chromosome 22 alteration was 5% in A, 33% in AA, and 38% in GB. This study demonstrated the advantages of combining array comparative genomic hybridization and microsatellite analysis in elucidating complex genomic rearrangements in primary human tumor tissue. Supplementary material for this article can be found on the Genes, Chromosomes and Cancer website at http://www.interscience.wiley.com/jpages/1045-2257/suppmat/index.html.     

Diverse chromosome breakage mechanisms underlie subtelomeric rearrangements, a common cause of mental retardation

Subtelomeric rearrangements are an important cause of both isolated and familial idiopathic mental retardation. A variety of different rearrangements such as pure truncations, unbalanced translocations, interstitial deletions, and inverted duplications have been detected throughout various screening studies. The cause of these aberrations is poorly understood as only few of the breakpoints have been determined and studied. We molecularly characterized the breakpoints of three rearrangements including a 1p subtelomeric deletion, a 1q subtelomeric deletion, and an unbalanced translocation between chromosomes 11q and 20q; we propose that diverse chromosome breakage mechanisms underlie subtelomeric rearrangements. The breakpoint sequences suggest that unusual non-B-DNA structures including triplex, tetraplex, and hairpin structures may be involved. In addition, we saw that the seemingly pure truncations of chromosomes 1p and 1q were in fact more complex rearrangements as highly repetitive sequences were joined to the chromosome end at the site of breakage.     

Characterization of the translocation breakpoint on chromosome 22q12.2 in a patient with neurofibromatosis type 2 (NF2)

We previously described a patient with neurofibromatosis type2 (NF2) who showed a constitutional balanced translocation,t(4; 22). To characterize the breakpoint on chromosome 22 inthis patient in relation to a candidate gene (NF2) responsiblefor NF2, we analyzed DNAs from this patient and her parentsusing parts of NF2 cDNA as probes. Southern analyses and DNAsequencing revealed that the chromosome 22 breakpoint in thispatient lies within the intron between exons 14 and 15 of NF2.The results lend support to the conclusion that NF2 is the generesponsible for the CNS form of neurofibromatosis.     

Identification of genetic aberrations on chromosome 22 outside the NF2 locus in schwannomatosis and neurofibromatosis type 2

Schwannomatosis is characterized by multiple peripheral and cranial nerve schwannomas that occur in the absence of bilateral 8th cranial nerve schwannomas. The latter is the main diagnostic criterion of neurofibromatosis type 2 (NF2), which is a related but distinct disorder. The genetic factors underlying the differences between schwannomatosis and NF2 are poorly understood, although available evidence implicates chromosome 22 as the primary location of the gene(s) of interest. To investigate this, we comprehensively profiled the DNA copy number in samples from sporadic and familial schwannomatosis, NF2, and a large cohort of normal controls. Using a tiling-path chromosome 22 genomic array, we identified two candidate regions of copy number variation, which were further characterized by a PCR-based array with higher resolution. The latter approach allows the detection of minute alterations in total genomic DNA, with as little as 1.5 kb per measurement point of nonredundant sequence on the array. In DNA derived from peripheral blood from a schwannomatosis patient and a sporadic schwannoma sample, we detected rearrangements of the immunoglobulin lambda (IGL) locus, which is unlikely to be due to a B-cell specific somatic recombination of IGL. Analysis of normal controls indicated that these IGL rearrangements were restricted to schwannomatosis/schwannoma samples. In the second candidate region spanning GSTT1 and CABIN1 genes, we observed a frequent copy number polymorphism at the GSTT1 locus. We further describe missense mutations in the CABIN1 gene that are specific to samples from schwannomatosis and NF2 and make this gene a plausible candidate for contributing to the pathogenesis of these disorders.     

Constitutional translocation t(4;22) (q12;q12.2) associated with neurofibromatosis type 2

We report on a female patient with bilateral acoustic neurinomas and other tumors in the central nervous system (neurofibromatosis type 2: NF2) and the constitutional translocation, t(4;22) (q12;q12.2). The precise identification of the translocation breakpoint (q12.2) on chromosome 22 implies the refined localization of a gene responsible for NF2, and would provide a clue to its molecular characterization and to the isolation of the gene. Chromosomes of a paraspinal neurinoma from the patient were also analyzed, and the same karyotype as seen in cultured peripheral lymphocytes was found. The patient's father was also a carrier of the translocation, but he had no clinical symptoms of NF2, nor did other relatives. Several explanations are offered for the different expression of the translocation between the patient and her father. © 1992 Wiley-Liss, Inc.     

Regional fine mapping of the β crystallin genes on chromosome 22 excludes these genes as physically linked markers for neurofibromatosis type 2

Neurofibromatosis type 2 (NF2) is a rare autosomal dominant disease, characterized by the development of bilateral vestibular schwannomas. The NF2 gene has been assigned to chromosome 22. Cataract and other eye abnormalities are frequently seen in NF2 patients. The specific association of eye abnormalities and NF2 might be caused by a genetic change on chromosome 22 that affects both the NF2 gene and a physically linked crystallin gene. In order to test this hypothesis, we regionally localized the known crystallin genes (i.e. CRYBB2, CRYBB2P1, CRYBB3, and CRYBA4) on chromosome 22. Crystallin gene-specific probes were hybridized to an extended panel of human x rodent somatic cell hybrids containing various portions of chromosome 22. It was found that all crystallin genes map to a very small region on chromosome 22 that is physically separate from the NF2 gene region by at least 160 kb of DNA. In addition, we found that the βB crystallin genes (CRYBB2, CRYBB2P1, and CRYBB3) are clustered on a 300 kb Sacll fragment and that the βA4 crystallin gene (CRYBA4) is not part of this cluster. We conclude that the ocular manifestations in many NF2 patients are probably not the primary consequence of rearrangements on chromosome 22 that involve both the NF2 gene and a nearby β crystallin gene.\\wiley5\wiley$\Wiley-JWPH\final\jwph471     

Constitutional chromosome aberrations as pathogenetic events in hematologic malignancies

A predisposition to tumor development is associated with some constitutional chromosomal abnormalities. Investigations of families with an apparent hereditary cancer and constitutional chromosome rearrangements have led to the molecular identification of tumor suppressor genes. Under the somatic mutation theory for the development of cancer, two mutational events are required. The first step may be a constitutional event and the second an acquired genetic mutation. Cytogenetic studies were performed on 5633 bone marrow specimens from patients with hematologic malignancies from a single institution. Fifty cases of constitutional chromosome aberrations were detected. Data collected from the literature and from our series are reviewed and compared with the incidence of specific constitutional chromosome aberrations in the newborn population. Possible mechanisms that may predispose individuals with constitutional chromosome aberrations to the development of a hematologic malignancy are reviewed.     

Constitutional translocation t(4;22) (q12;q12.2) associated with neurofibromatosis type 2.

We report on a female patient with bilateral acoustic neurinomas and other tumors in the central nervous system (neurofibromatosis type 2: NF2) and the constitutional translocation, t(4;22) (q12;q12.2). The precise identification of the translocation breakpoint (q12.2) on chromosome 22 implies the refined localization of a gene responsible for NF2, and would provide a clue to its molecular characterization and to the isolation of the gene. Chromosomes of a paraspinal neurinoma from the patient were also analyzed, and the same karyotype as seen in cultured peripheral lymphocytes was found. The patient's father was also a carrier of the translocation, but he had no clinical symptoms of NF2, nor did other relatives. Several explanations are offered for the different expression of the translocation between the patient and her father.     

Clonal chromosome rearrangements in a uterine myoma

A cytogenetic study of a myoma of uterus with extensive hyaline, myxoid, and cystic degeneration revealed a clonal karyotype with a complex structural rearrangement involving chromosomes #3, #12, #14, #17, and #22. The modal chromosome number of the tumor was 45 due to monosomy #22. Analysis of seven additional myomas of the uterus including five tumors with typical histology and two with degenerative changes showed no clonal abnormalities. Single metaphases with a trisomy and a translocation were detected in two tumors. We conclude that although many uterine myomas appear to have normal karyotypes, clonal chromosome abnormalities are present in some of these tumors.     

Constitutional 11q14-q22 chromosome deletion syndrome in a child with neuroblastoma MYCN single copy

Constitutional 11q deletion is a chromosome imbalance possibly found in MCA/MR patients analyzed for chromosomal anomalies. Its role in determining the phenotype depends on extension and position of deleted region. Loss of heterozygosity of 11q (region 11q23) is also associated with neuroblastoma, the most frequent extra cranial cancer in children. It represents one of the most frequent cytogenetic abnormalities observed in the tumor of patients with high-risk disease even if germline deletion of 11q in neuroblastoma is rare. Hereby, we describe a 18 months old girl presenting with trigonocephaly and dysmorphic facial features, including hypotelorism, broad depressed nasal bridge, micrognathia, synophrys, epicanthal folds, and with a stage 4 neuroblastoma without MYCN amplification, carrying a germline 11q deletion (11q14.1-q22.3), outside from Jacobsen syndrome and from neuroblastoma 11q critical regions. The role of 11q deletion in determining the clinical phenotype and its association with neuroblastoma development in the patient are discussed.     

Mitotic recombination of chromosome arm 17q as a cause of loss of heterozygosity of NF1 in neurofibromatosis type 1-associated glomus tumors

Neurofibromatosis type 1 (NF1) is a common, autosomal dominant, tumor-predisposition syndrome that arises secondary to mutations in NF1. Glomus tumors are painful benign tumors that originate from the glomus body in the fingers and toes due to biallelic inactivation of NF1. We karyotyped cultures from four previously reported and one new glomus tumor and hybridized tumor (and matching germline) DNA on Illumina HumanOmni1-Quad SNP arrays (≈ 1 × 10(6) SNPs). Two tumors displayed evidence of copy-neutral loss of heterozygosity of chromosome arm 17q not observed in the germline sample, consistent with a mitotic recombination event. One of these two tumors, NF1-G12, featured extreme polyploidy (near-tetraploidy, near-hexaploidy, or near-septaploidy) across all chromosomes. In the remaining four tumors, there were few cytogenetic abnormalities observed, and copy-number analysis was consistent with diploidy in all chromosomes. This is the first study of glomus tumors cytogenetics, to our knowledge, and the first to report biallelic inactivation of NF1 secondary to mitotic recombination of chromosome arm 17q in multiple NF1-associated glomus tumors. We have observed mitotic recombination in 22% of molecularly characterized NF1-associated glomus tumors, suggesting that it is a not uncommon mechanism in the reduction to homozygosity of the NF1 germline mutation in these tumors. In tumor NF1-G12, we hypothesize that mitotic recombination also "unmasked" (reduced to homozygosity) a hypomorphic germline allele in a gene on chromosome arm 17q associated with chromosomal instability, resulting in the extreme polyploidy.     

Paternal isodisomy for chromosome 2 as the cause of Crigler-Najjar type I syndrome

Crigler-Najjar syndrome type I (CN-I) is a rare and severe autosomal recessive metabolic disease due to a total deficiency of bilirubin uridine diphosphate glucuronosyltransferase located on chromosome 2. We report on a child with CN-I due to a phenylalanine residue deletion inherited only from the father carrying this deletion at the heterozygous state. Cytogenetic analyses showed no deletion of the chromosomal 2q37 region. Microsatellite analysis of the child and his parents was consistent with paternal isodisomy for chromosome 2 in the child. This report demonstrates that uniparental disomy may be at the origin of very rare diseases transmitted as autosomal recessive traits and emphasizes the need for parental DNA analysis in such cases.     

Two unrelated clonal chromosome rearrangements in a nasal papilloma

We have cytogenetically examined short-term cultures from a nasal papilloma, a tumor type in which chromosome aberrations have hitherto not been reported. Two pseudodiploid clones were detected, giving the tumor karyotype 46,XY,t(1;3)(p31;p12)/46,XY,t(11;?)(q25;?).