Submicroscopic duplication of chromosome 21 and trisomy 21 phenotype (Down syndrome)

Familial 4.3 Mb duplication of 21q22 sheds new light on the Down syndrome critical region

A 4.3 Mb duplication of chromosome 21 bands q22.13-q22.2 was diagnosed by interphase fluorescent in situ hybridisation (FISH) in a 31 week gestational age baby with cystic hygroma and hydrops; the duplication was later found in the mother and in her 8-year-old daughter. All had the facial gestalt of Down syndrome (DS). This is the smallest accurately defined duplication of chromosome 21 reported with a DS phenotype. The duplication encompasses the gene DYRK1 but not DSCR1 or DSCAM. Previous karyotype analysis and telomere screening of the mother, and karyotype analysis and metaphase FISH of a chorionic villus sample, had all failed to reveal the duplication. The findings in this family add to the identification and delineation of a "critical region" for the DS phenotype on chromosome 21.

BAC-FISH assays delineate complex chromosomal rearrangements in a case of post-Chernobyl childhood thyroid cancer

Structural chromosome aberrations are known hallmarks of many solid tumors. In the papillary form of thyroid cancer (PTC), for example, activation of the receptor tyrosine kinase (RTK) genes, RET and neurotrophic tyrosine kinase receptor type I (NTRK1) by intra- and interchromosomal rearrangements has been suggested as a cause of the disease. However, many phenotypically similar tumors do not carry an activated RET or NTRK-1 gene or express abnormal ret or NTRK-1 transcripts. Thus, we hypothesize that other cellular RTK-type genes are aberrantly expressed in these tumors. Using fluorescence in situ hybridization-based methods, we are studying karyotype changes in a relatively rare subgroup of PTCs, i.e., tumors that arose in children following the 1986 nuclear accident in Chernobyl, Ukraine. Here, we report our technical developments and progress in deciphering complex chromosome aberrations in case S48TK, an aggressively growing PTC cell line, which shows an unusual high number of unbalanced translocations.

Familial 4.3 Mb duplication of 21q22 sheds new light on the Down syndrome critical region

A 4.3 Mb duplication of chromosome 21 bands q22.13-q22.2 was diagnosed by interphase fluorescent in-situ hybridisation (FISH) in a 31-week gestational age baby with cystic hygroma and hydrops; the duplication was later found in the mother and in her 8-year-old daughter by the same method and confirmed by array comparative genomic hybridisation (aCGH). All had the facial gestalt of Down syndrome (DS). This is the smallest accurately defined duplication of chromosome 21 reported with a DS phenotype. The duplication encompasses the gene DYRK1 but not DSCR1 or DSCAM, all of which have previously been implicated in the causation of DS. Previous karyotype analysis and telomere screening of the mother, and karyotype analysis and metaphase FISH of a chorionic villus sample, had all failed to reveal the duplication. The findings in this family add to the identification and delineation of a "critical region" for the DS phenotype on chromosome 21. Cryptic chromosomal abnormalities can be missed on a routine karyotype for investigation of abnormal prenatal ultrasound findings, lending support to the use of aCGH analysis in this setting.

Clinical, cytogenetic, and molecular genetic characterization of two unrelated patients with different duplications of 21q

We present 2 patients with dup(21q). Patient MP01 had mild mental retardation, facial findings characteristic of Down syndrome (DS), and a terminal duplication of chromosome 21. His karyotype was 46,XY,dup(21) (q22.1-qter). Patient MP03 had mild mental retardation, minor anomalies not characteristic of DS, and a duplication of the proximal long arm of chromosome 21, karyotype 46,XX,dup(21) (q11.2-q21.2). The patients were studied with single-copy DNA sequences from 20 loci on chromosome 21 to characterize the extent of the duplicated regions at the DNA level. DNA loci from D21S55 to COL6A1 were triplicated in patient MP01 while loci from D21S13 to D21S8 were triplicated in patient MP03. Our results support the hypothesis of a critical region of chromosome 21, which in triplicate is responsible for many of the facial changes associated with DS. Other genes outside this region may also contribute to other abnormalities observed in DS.

Clinical, cytogenetic, and molecular evaluation of a patient with partial trisomy 21 (21q11-q22) lacking the classical Down syndrome phenotype

The clinical, cytogenetic, and molecular studies of an individual are presented here for the purpose of further characterizing what regions of chromosome 21q are essential for expression of the typical Down syndrome phenotype. This individual had a de novo, unbalanced translocation chromosome interpreted as: 45,XX,t(18;dup[21q]). Physical examination revealed mild manifestations, but not the typical phenotype of Down syndrome. The patient was studied using 20 single copy probes known to map to the 21q region. DNA polymorphism and dosage analyses showed triplication of loci D21S13 through D21S58 involving 21q11 to 21q22.1, and possibly involving the 21q22.2 region. Her clinical presentation, which did not include the classical findings of Down syndrome, suggests that regions distal to 21q22.1, when present in triplicate dose, account for the major manifestations of the classical phenotype. However, duplication of the area between the centromere and 21q22.1 may contribute to some of the other abnormalities in Down syndrome.

The Down syndrome critical region

Since the early 1970's numerous attempts have been made to learn whether specific segments of chromosome 21, when triplicated, are responsible for the clinical condition Down syndrome (DS). Studies were reported in which positive or negative clinical diagnoses of DS were made in the presence of partial trisomy of one or another segment of the chromosome. The distal half of the long arm of 21 (21q22) possesses most of the gene transcribing sites of the chromosome. It was this region that was thought to contain loci essential to production of the clinical syndrome. Subsequent studies identified subregions of this band as "minimal" or "critical" sites necessary and sufficient to produce the clinical condition. A major problem with these assignments was that different investigators defined different critical/minimal regions. In 1994 evidence was presented in which regions of most of the long arm of chromosome 21 were said to contribute to the DS phenotype. Soon after, a report described a child with DS and partial tetrasomy of the short arm and proximal long arm of 21, segments clearly distinct from the previously identified critical areas. Thus the clinical diagnosis of DS can be made in the presence of partial aneuploidy of nearly all segments of chromosome 21. It must be concluded that no evidence exists that individual loci on 21 are singularly responsible for specific phenotypic abnormalities in DS. Without exception, each of the clinical findings associated with DS is a multifactorial trait. The analysis of each trait in DS should thus be similar to analyses of the same traits in the general population with a focus on the way aneuploidy affects expression of multifactorial characteristics.

Loss of olfactory function in dementing disease

Alzheimer's (AD) patients show neuropathological changes in areas of the brain central to olfactory processing, suggesting the theoretical importance and potential diagnostic utility of investigating functional changes in olfaction in these patients. Persons with Down's Syndrome who live to the fourth decade develop neuropathological changes in the brain similar to those found in AD. A series of investigations have been conducted to assess olfaction function in both patients with Alzheimer's disease and persons with Down's Syndrome. Functional testing included olfactory threshold, odor identification, odor similarity judgements, odor recognition memory, odor recall, odor fluency. Both Alzheimer's patients and persons with Down's Syndrome showed significant impairment in olfactory function, with some measures showing more impairment than others in the early stages of the disease process. Longitudinal investigation of several of the measures indicated decreased function over time consonant with falling DRS scores. Normal controls who tested positive for the APOE4 allele showed impaired odor identification compared to those who were allele negative. Patients with Huntington's Disease showed olfactory functional impairments, although the degree of impairment differed from the cortical dementias for some of these tasks. The sensitivity and specificity of these assessments will be discussed in relation to analogous assessments in other sensory modalities.

A brief review of cryptic duplications of 21q as an emerging cause of Down syndrome: practical considerations for accurate detection

We review five cryptic duplications of 21q in patients with Down syndrome (DS) that were inherited from parental balanced translocations. All cases were identified by fluorescence in situ hybridization (FISH) and or DNA diagnosis because the phenotype was inconsistent with the initial cytogenetic studies. These rearrangements seem to escape detection without expanded testing and are probably more frequent than expected. For this reason we propose a series of steps combining objective clinical diagnostic criteria, FISH and DNA methods to achieve an accurate ascertainment.

Trisomy 21 and accelerated aging: DNA-repair parameters in peripheral lymphocytes of Down's syndrome patients

Down's syndrome (DS) cases from 1-40 years of age and showing no other anomalies or deficiencies were categorized into three age groups: group 1, < or = 12 years; group 2, 13-25 years; and group 3, > or = 26 years. The DNA-repair markers like unscheduled DNA synthesis (UDS), activities of DNA polymerases, (Total, beta and epsilon) and two endodeoxyribonucleases, (UV- and AP-DNases) were assessed in the peripheral lymphocytes of these subjects (under different conditions) along with age and sex matched normal healthy human subjects. The DS group showed lower DNA-repair efficiency and also an accelerated decline in DNA-repair capacity with age. These results indicate that deteriorated DNA-repair potential could be one of the probable reasons for premature aging seen in this chromosomal disorder.

Comparison of the 5' end of the rat and mouse cystathionine beta-synthase genes

We have isolated and characterized a genomic fragment encompassing the first six exons and 2.6 kbp 5' flanking sequence of the rat cystathionine beta-synthase (CBS) gene. A previously unknown exon approximately 3 kbp upstream of exon 1 was identified. The transcription start site was mapped to approximately 3 kbp upstream from the translation start codon and contains a consensus cap signal. The putative promoter region contains three GC boxes, in both orientations, and no TATA box. We have also compared a 1171-bp-long DNA sequence of the 5' end of the rat CBS gene with the homologous mouse region of 1125 bp. We found two homologous Sp1 sites in the mouse gene and an overall sequence conservation of 70% with 88-89% similarity in the 80-bp regions surrounding the intron 0 splice sites.

Molecular analysis of chromosome 21 in a patient with a phenotype of Down syndrome and apparently normal karyotype

Down syndrome (DS) is caused in most cases by the presence of an extra chromosome 21. It has been shown that the DS phenotype is produced by duplication of only a small part of the long arm of chromosome 21, the 21q22 region, including and distal to locus D21S55. We present molecular investigations on a woman with clinically typical DS but apparently normal chromosomes. Her parents were consanguineous and she had a sister with a DS phenotype, who died at the age of 15 days. Repeated cytogenetic investigations (G-banding and high resolution banding) on the patient and her parents showed apparently normal chromosomes. Autoradiographs of quantitative Southern blots of DNAs from the patient, her parents, trisomy 21 patients, and normal controls were analyzed after hybridization with unique DNA sequences regionally mapped on chromosome 21. Sequences D21S59, D21S1, D21S11, D21S8, D21S17, D21S55, ERG, D21S15, D21S112, and COL6A1 were all found in two copies. Fluorescent in situ hybridization with a chromosome 21-specific genomic library showed no abnormalities and only two copies of chromosome 21 were detected. Nineteen markers from the critical region studied with polymerase chain reaction amplification of di- and tetranucleotide repeats did not indicate any partial trisomy 21. From this study we conclude that the patient does not have any partial submicroscopic trisomy for any segment of chromosome 21. It seems reasonable to assume that she suffers from an autosomal recessive disorder which is phenotypically indistinguishable from DS.

Down syndrome with partial duplication and del (21) syndrome: study protocol and call for collaboration. Study I: Clinical assessment

We report on the clinical and cytogenetic assessment of five cases of Down syndrome phenotype with either a partial duplication of chromosome 21 or a normal karyotype, and we quote a case of del (21q) syndrome. Down syndromes with a partial duplication of chromosome 21 (as well as cases of del (21q), which are partly the phenotypic countertype of trisomy 21) are of paramount importance in the understanding of genes involved in the phenotype of Down syndrome. The goal is to find the relevant genes implicated in the main traits of Down syndrome (i.e. mental retardation, Alzheimer disease, and serious visceral malformations). Such a goal, in our opinion, cannot be reached just by publishing the genotype and the phenotype of a small cohort of patients: 1. a sufficient number of accurate cases is needed, and 2. data have to be computerized for definite conclusions to be reached. The main aims of this report are to present our study protocol and to invite colleagues to participate in a collaborative study in order to collect a maximum of these (rare) cases.

Genomic damage and its repair in young and aging brain

A brief review of the available information concerning age-related genomic (DNA) damage and its repair, with special reference to brain tissue, is presented. The usefulness of examining the validity of DNA-damage and repair hypothesis of aging in a postmitotic cell like neuron is emphasized. The limited number of reports that exist on brain seem to overwhelmingly support the accumulation of DNA damage with age. However, results regarding the age-dependent decline in DNA-repair capacity are conflicting and divided. The possible reasons for these discrepancies are discussed in light of the gathering evidence, including some human genetic disorders, to indicate how complex is the DNA-repair system in higher animals. It is suggested that assessment of repair potential of neurons with respect to a specific damage in a specific gene might yield more definitive answers about the DNA-repair process and its role in aging.

DNA damage and repair in brain: relationship to aging

The usefulness of conducting DNA damage and repair studies in a postmitotic tissue like brain is emphasized. We review studies that use brain as a tissue to test the validity of the DNA damage and repair hypothesis of aging. As far as the accumulation of age dependent DNA damage is concerned, the data appear to overwhelmingly support the hypothesis. However, attempts to demonstrate a decline in DNA repair capacity as a function of age are conflicting and equally divided. Possible reasons for this discrepancy are discussed. It is suggested that assessment of the repair capacity of neurons with respect to a specific type of damage in a specific gene might yield more definitive answers regarding the role of DNA repair potential in the aging process and as a longevity assurance system.

San Luis Valley recombinant chromosome 8 and tetralogy of Fallot: a review of chromosome 8 anomalies and congenital heart disease

Tetralogy of Fallot, the most common cyanotic heart defect, has not been closely associated with a specific chromosome defect. The San Luis Valley Recombinant Chromosome 8 [SLV Rec(8)] syndrome is strongly associated with congenital heart disease, particularly tetralogy of Fallot. This article reviews SLV Rec(8) syndrome and other chromosome 8 aberrations to suggest locations for cardiogenic genes. SLV Rec(8) [rec(8),dup q,inv(8)(p23q22)] syndrome has been found in Hispanic families in the southwestern United States. Congenital heart disease is found in 93.3% of SLV Rec(8) individuals (n = 45), with tetralogy of Fallot constituting 40.5% of all lesions and conotruncal defects, 55.6%. These frequencies exceed the incidence of tetralogy of Fallot (10%) and conotruncal defects (20%) among all children with heart defects (P less than 0.003 for both). Review of patients with deletion 8p (n = 13) showed heart defects in 84.6% with 27.3% being conotruncal defects. Among duplication 8q patients (n = 20), 45% had heart defects with conotruncal defects constituting 44%. Neither group differed significantly from expected in its incidence of conotruncal defects. Among patients with mosaic trisomy 8 (n = 47), 12 had heart abnormalities including one conotruncal defect. Among 3 patients with other rec(8) chromosomes, one had a ventricular septal defect. The cause of heart defects in SLV Rec(8) cannot be assigned to either the deletion of 8p or the duplication of 8q. The lack of an association between other chromosome 8 abnormalities and tetralogy of Fallot suggests that genes at the SLV Rec(8) breakpoints or an interaction between genes on both arms of chromosome 8 are important.

Increased SOD1 enzymatic activity and gene modifications in orangutans: evolutionary implications

Superoxide dismutase CuZn (SOD1) enzymatic activity was measured in five orangutans (Pongo pygmaeus, PPY) and compared to that of man, chimpanzee, and gorilla. It was found to be increased by a factor of two in one orangutan (Ralfina) and by a factor of 1.5 in the four others. In situ hybridization of the SOD1 cDNA human probe showed a heterozygous intra-chromosomal rearrangement of pair PPY XXI, possibly an insertion, in Ralfina. Southern blotting showed that the SOD1 gene is modified in the three orangutans that were investigated and that a further modification of the 5'-end of the gene had occurred in Ralfina. The evolutionary implications of these observations are discussed.

Distal deletion of chromosome 1q in an adult

An adult patient with mongoloid appearance, profound retardation and autistic-like behavior was found to have a deletion of the distal bands of chromosome 1q. To our knowledge, this is the oldest patient with distal deletion 1q.

Critical role of the D21S55 region on chromosome 21 in the pathogenesis of Down syndrome

The duplication of a specific region of chromosome 21 could be responsible for the main features of Down syndrome. To define and localize this region, we analyzed at the molecular level the DNA of two patients with partial duplication of chromosome 21. These patients belong to two groups of Down syndrome patients characterized by different partial trisomies 21: (i) duplication of the long arm, proximal to 21q22.2, and (ii) duplication of the end of the chromosome, distal to 21q22.2 We assessed the copy number of five chromosome 21 sequences (SOD1, D21S17, D21S55, ETS2, and D21S15) and found that D21S55 was duplicated in both cases. By means of pulsed-field gel analysis and with the knowledge of regional mapping of the probes D21S17, D21S55 and ETS2, we estimated the size of the common duplicated region to be between 400 and 3000 kilobases. This region, localized on the proximal part of 21q22.3, is suspected to contain genes the overexpression of which is crucial in the pathogenesis of Down syndrome.

Trisomy 21q223 and Down's phenotype correlation evidenced by in situ hybridization

Two cases of trisomy 21q223 with the Down's phenotype were analysed by in situ hybridization with specific probes previously located in the sub-bands 21q221 (SOD-A) and 21q223 (BCEI and COL6A). These studies give evidence that the clinical picture of Down's syndrome is at least to a great extent correlated with trisomy for the 21q223 band.

Human ETS2 gene on chromosome 21 is not rearranged in Alzheimer disease

The human ETS2 gene, a member of the ETS gene family, with sequence homology with the retroviral ets sequence of the avian erythroblastosis retrovirus E26 is located on chromosome 21. Molecular genetic analysis of Down syndrome (DS) patients with partial trisomy 21 allowed us to reinforce the supposition that ETS2 may be a gene of the minimal DS genetic region. It was originally proposed that a duplication of a portion of the DS region represents the genetic basis of Alzheimer disease, a condition associated also with DS. No evidence of either rearrangements or duplications of ETS2 could be detected in DNA from fibroblasts and brain tissue of Alzheimer disease patients with either the sporadic or the familiar form of the disease. Thus, an altered ETS2 gene dosage does not seem to be a genetic cause or component of Alzheimer disease.

Molecular genetics of superoxide dismutases

Molecular genetics of SOD has been recently developed primarily due to the new biotechnologies. Different types of isoenzymes have now been cloned and sequenced from several species ranging from bacteria to human and plants. Knowledge of the nucleotide sequences permitted refinement of structural models and provided information on subcellular locations. Cloned genes allowed the production of large amounts of SOD. They have been used for physiological and regulation studies, structural and enzymatic analyses, and are vital tools for the isolation of mutants. Isolation of mutants is generally essential to the understanding of the biological function of the gene in question. Indeed, SOD deficient mutants have now been isolated in bacteria and yeast. Their properties support, at numerous levels, a major role of SOD in cellular defense against oxygen toxicity. Few data are presently available on the molecular basis of mechanisms that regulate the expression of SOD.