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Objective. We investigated whether the concentration of the glycoprotein fetuin A is altered in the second trimester amniotic fluid of trisomy 21 pregnancies compared with euploid pregnancies. Methods. 25 pregnancies with an extra chromosome 21 were matched for maternal and gestational age with 25 pregnancies with normal karyotype. Levels of fetuin A in amniotic fluid were measured by a commercially available enzyme-linked immunosorbent assay (ELISA) kit. Results. The median concentration of fetuin A in amniotic fluid of trisomy 21 pregnancies (5.3 ng/ml) was statistically significantly lower (P value=0.008) compared with that in euploid pregnancies (6.8 ng/mL). Conclusion. Lower levels of fetuin A in trisomy 21 may indicate an association with altered metabolic pathways in this early stage that could potentially be associated with features of the syndrome, such as growth restriction or impaired osteogenesis.

In the light of modern molecular technologies, the understanding of the complexity of the numerous genotype-phenotype correlations regarding Dravet syndrome is mandatory. Motivated by 2 patients, whose whole-exome sequencing revealed novel mutations that exemplify the phenotypic and genetic heterogeneities associated with typical and atypical Dravet syndrome presentations, the authors discuss the existence of a broader spectrum of Dravet syndrome. The first patient is a 4-year-old boy with fairly typical Dravet syndrome and a novel sodium channel α1 subunit gene mutation of high-predicted combined pathogenicity likelihood. The second patient is a 15-year-old boy with some atypical features of Dravet syndrome, harboring a novel mutation of the γ-aminobutyric acid receptor α1 subunit gene, whose role in this syndrome pathogenesis has recently been highlighted. A brief review of the literature reveals that none of the current diagnostic criteria is thoroughly predictive of the disease, and phenotypic discrepancies are common among patients carrying atypical Dravet syndrome mutations. The authors conclude that the discussion of a Dravet syndrome spectrum is relevant., Competing Interests: Declaration of Conflicting Interests: The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Fetal malformations detected through routine prenatal ultrasound examination comprise a heterogeneous group potentially associated with genetic disorders where the underlying cause is difficult to establish. We present the prenatal diagnosis of a rare X-linked myopathy involving a new VMA21 gene mutation, detected through a novel prenatal exome sequencing-based approach.

Background: Although several studies in various countries have indicated that the presence of the E4 allele of the apolipoprotein-E (APOE) gene is a risk factor for ischemic cerebrovascular disease, the strength of this association still remains a matter of debate., Objectives: The aim of the study was to determine the frequency of the APOE E4 allele and various other gene polymorphisms in in a well-characterized sample of Greek patients and to evaluate the potential associations with the risk of ischemic stroke (IS) and coronary heart disease (CHD)., Material and Methods: A total of nine gene variants/polymorphisms - F5 (Leiden - R5 06Q, rs6025), F2 (20210G > A, rs1799963), F13A1 (V34L, rs5985), MTHFR (677C > T - A222V, rs1801133), MTHFR (1298A > C - E429A, rs1801131), FGB (-455G > A -c.-463G > A; rs1800790), SERPINE1 (PAI14G/5G - rs1799889), ACE (ACE I/D, rs1799752), ITGB3 (GPIIIa L33P, rs5918) and the APOE E2/E3/E4 alleles (rs7412, rs429358) - were genotyped in 200 newly diagnosed ischemic stroke (IS) patients, 165 patients with ischemic coronary heart disease (CHD) and 159 controls with no cerebroor cardiovascular disease (non-CVD). A statistical analysis was performed using univariate and multivariate logistic regression models., Results: No significant association was found regarding most gene polymorphisms and the presence of IS or CHD in the patient cohort. However, the APOE E4 allele frequency was significantly higher (p = 0.02) among patients with ischemic stroke (IS) or IS + CHD (12.7%) when compared to the controls (5.1%). More accurately, E4 carriers had 2.66 and 2.71 times greater likelihood of IS or IS + CHD than non-carriers, respectively (OR = 2.66, 95% CI 1.39-5.07, OR = 2.71, 95% CI 0.98-7.48)., Conclusions: In contrast to some previous studies, these results support the role of the APOE E4 allele as an independent risk factor for ischemic stroke and ischemic coronary heart disease among Greek patients.

Background. Fetal malformations and other structural abnormalities are relatively frequent findings in the course of routine prenatal ultrasonographic examination. Due to their considerable genetic and clinical heterogeneity, the underlying genetic cause is often elusive and the resulting inability to provide a precise diagnosis precludes proper reproductive and fetal risk assessment. We report the development and first applications of an expanded exome sequencing-based test, coupled to a bioinformatics-driven prioritization algorithm, targeting gene disorders presenting with abnormal prenatal ultrasound findings. Methods. We applied the testing strategy to14 euploid fetuses, from 11 on-going pregnancies and three products of abortion, all with various abnormalities or malformations detected through prenatal ultrasound examination. Whole exome sequencing (WES) was followed by variant prioritization, utilizing a custom analysis pipeline (Fetalis algorithm), targeting 758 genes associated with genetic disorders which may present with abnormal fetal ultrasound findings. Results. A definitive or highly-likely diagnosis was made in 6 of 14 cases (43%), of which 3 were abortuses (Ellis-van Creveld syndrome, Ehlers-Danlos syndrome and Nemaline myopathy 2) and 3 involved on-going pregnancies (Citrullinemia, Noonan syndrome, PROKR2-related Kallmann syndrome). In the remaining eight on-going pregnancy cases (57%), a ZIC1 variant of unknown clinical significance was detected in one case, while in seven cases testing did not reveal any pathogenic variant(s). Pregnancies were followed-up to birth, resulting in one neonate harboring the PROKR2 mutation, presenting with isolated minor structural cardiac abnormalities, and in seven apparently healthy neonates. Discussion. The expanded targeted exome sequencing-based approach described herein (Fetalis), provides strong evidence suggesting a definite and beneficial increase in our diagnostic capabilities in prenatal diagnosis of otherwise chromosomally balanced fetuses with troubling ultrasound abnormalities. Furthermore, the proposed targeted exome sequencing strategy, designed primarily as a diagnostic rather than a research discovery tool, overcomes many of the problems and limitations associated with clinical wide-scale WES testing in a prenatal setting.

Introduction: The aim of this article is to provide a perspective of prenatal chromosomal diagnosis (PCD) derived from a single center's evolving experience from ∼90,000 consecutive prenatal cases and to highlight important issues and current dilemmas., Materials and Methods: Prenatal cases in this study (1985-2013) were referred for various indications, and PCD was performed by standard karyotype in 84,255 cases, multiplex ligation-dependent probe amplification (MLPA) panel in 3,010 cases and standalone array comparative genomic hybridization (aCGH) in 3,122 cases., Results: Classic karyotype revealed 1.7 and 7.9% of pathological cases in amniotic fluid and CVS samples, respectively, with common aneuploidies accounting for 59.6 and 64.3% of the total abnormal. Molecular approaches increased the diagnostic yield by 0.6% for MLPA and 1.6% for aCGH, uncovering pathogenic chromosomal abnormalities undetectable by karyotype analysis., Conclusions: Current molecular diagnostic capabilities and the recent introduction of noninvasive prenatal testing (NIPT) point to one current major dilemma in PCD, with serious implications in genetic counseling, relating on the one hand to reaping the benefits from the high detection rate afforded through aCGH but accepting an invasive risk, and on the other hand, offering a lower detection rate practically only for Down syndrome, with minimal invasive risk., (© 2015 S. Karger AG, Basel.)

Objective: The presence of numerical and/or structural chromosomal abnormalities is a frequent finding in clonal hematopoietic malignant disease, typically diagnosed through routine karyotyping and/or fluorescent in situ hybridization (FISH) analysis. Recently, the application of array comparative genomic hybridization (aCGH) has uncovered many new cryptic genomic copy number imbalances, most of which are now recognized as clinically useful markers of haematological malignancies. In view of the limitations of both FISH and aCGH techniques, in terms of their routine application as a first line screening test, we designed a new multiple ligation-dependent probe amplification (MLPA) probemix for use in addition to classic karyotype analysis., Methods: A novel MLPA probemix was developed to interrogate copy number changes involving chromosomal regions: 2p23-24 (MYCN, ALK), 5q32-34 (MIR145A, EBF1, MIR146A), 6q21-27, 7p12.2 (IKZF1), 7q21-36, 8q24.21 (MYC), 9p24 (JAK2 V617F point mutation), 9p21.3 (CDKN2A/2B), 9p13.2 (PAX5), 10q23 (PTEN), 11q22.3 (ATM), 12p13.2 (ETV6), 13q14 (RB1, MIR15A, DLEU2, DLEU1), 17p13.1 (TP53), and 21q22.1 (RUNX1/AML1) and was applied to DNA extracted from 313 consecutive bone marrow patient samples, referred for routine karyotype analysis., Results: More than half of the samples originated from newly investigated patients. We discovered clinically relevant genomic aberrations, involving a total of 24 patients (8%) all with a normal karyotype, which would have remained undiagnosed., Discussion: Our data clearly indicate that routine application of this MLPA screening panel, as an adjunct to karyotype analysis, provides a sensitive, robust, rapid and low-cost approach for uncovering clinically important genomic abnormalities, which would have otherwise remained undetected.

A 33-year-old adult male of Greek ethnicity, with hematological indices suggesting β(0)-thalassemia (β(0)-thal) trait, was investigated for HBB gene mutations in the course of preparation for preimplantation genetic diagnosis (PGD). Application of a routine diagnostic protocol, consisting of sequence analysis of the HBB gene, coupled to multiplex ligation-dependent probe amplification (MLPA), identified a single nucleotide deletion (-T) at codon 72 [HBB: c.216delT], leading to a novel pathogenic frameshift and protein-truncating β(0)-thal mutation (p.Phe72LeufsX18).

Objective: To present the application of multiplex ligation-dependent probe amplification (MLPA)-based screening approach in 1550 typical prenatal cases, for the simultaneous targeted detection of 23 recurrent microdeletion syndromes as well as subtelomeric copy number assessment for all chromosomes and discuss the implications in routine prenatal chromosomal diagnosis (PCD)., Methods: Following amniocentesis or chorionic villus sampling, samples were processed for routine karyotype analysis while DNA was extracted in parallel for MLPA analysis. When necessary, parental samples were analyzed to determine the inheritance of the detected aberrations., Results: This panel has been applied since 2006 in 1550 prenatal samples, referred for routine karyotype analysis, with (16.1%) or without (77.7%) ultrasound (US) findings. We identified eight fetuses with pathological genomic abnormalities (approximately 1 in 193), five of which had as sole indication advanced maternal age (1 in 240). In two cases an abnormality was suspected from karyotype analysis, while the remaining six cases would have otherwise remained totally undetected., Conclusions: Our data represent the largest published series involving this type of genomic analysis in routine prenatal diagnosis, without indication bias. The panel increases significantly the diagnostic yield of conventional PCD and does not pose interpretation problems., (Copyright © 2011 John Wiley & Sons, Ltd.)

Objective: Presentation of a novel case, involving the design and implementation of preimplantation genetic diagnosis (PGD) for cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL)., Methods: The disease-causing mutation, c.459C>T (R153C) in exon 4 of the Notch3 gene, was previously identified in the affected father. The family already had a pregnancy termination following prenatal diagnosis and chose to undergo PGD. A PGD protocol was designed to include informative, linked short tandem repeat (STR) markers and an intragenic single nucleotide polymorphism (SNP), coupled to mutation identification. Biopsy was performed at day 3 and blastocysts were transferred on day 5 after fertilization. Standard prenatal diagnosis procedures were employed to confirm the PGD results., Results: One blastomere was removed at day 3 from each of eight embryos. Detection of the c.459C>TNotch3 mutation, coupled to informative polymorphic markers, unambiguously identified three unaffected embryos. Blastocyst transfer resulted in a singleton pregnancy and subsequent prenatal diagnosis confirmed that the fetus was disease-free., Conclusions: Given the dominant, highly penetrant and potentially serious effects of Notch3 mutations, PGD for CADASIL may be considered and implemented as a reproductive option, following proper genetic counseling.

Objective: The implementation and evaluation of a proposed wide-scale prenatal screening strategy, based on DNA isolated from dried blood spots in the first trimester of pregnancy, for the early detection of pregnancies at risk for cystic fibrosis (CF)., Methods: The screening was performed in conjunction with routine biochemical marker screening for Down's syndrome risk in the first trimester of pregnancy. DNA was isolated from 1,233 dried blood spots and analyzed for the presence of the CF transmembrane regulator DeltaF508 mutation. Women carriers were offered and accepted the option for additional full testing of their partners in order to assess the risk for the fetus., Results: All 1,233 samples were successfully analyzed, identifying 23 DeltaF508 carriers, corresponding to a DeltaF508 carrier rate of approximately 1/55 (1.8%). All partners of the women carriers were further tested without revealing any need for further prenatal testing in this group., Conclusions: This study reveals the relatively high frequency of the DeltaF508 CF mutation in the Greek population. More importantly, we demonstrate that the proposed prenatal screening strategy, based on the ease and cost-effectiveness of the analysis for the detection of a single common mutation, can be considered as a feasible and practical approach for wide-scale prenatal screening for CF, following the sequential model. It is applied early on in pregnancy, allowing for the timely management of families at risk for the corresponding genetic disorders. Finally, it can easily be extended to include screening for other common genetic disorders in specific population groups.

Tetrasomy 8 is an extremely rare chromosome abnormality, one that has been reported in only a few cases with myeloid malignancies. The majority of reported cases consist of acute myelogenous leukemias (AML) of monocytic lineage. In slightly more than half of the patients, tetrasomy 8 was the single cytogenetic abnormality. Fluorescence in situ hybridization revealed tetrasomy 8 and trisomy 8 concurrently in all but one of the bone marrow samples. The clonal relationship between trisomy 8 and tetrasomy 8 in these cases remains to be clarified. Patients with tetrasomy 8 have a poor prognosis, and only 1 out of 33 patients was free of disease 3 years after autologous bone marrow transplantation. Here, we report the case of a 25-year-old female patient with monocytic leukemia and tetrasomy 8.

Background and Objectives: Early lymphoid differentiation is characterized by antigen receptor gene rearrangements; the rearrangement process is governed by two lymphoid-specific genes, RAG (recombinase activating gene)-1 and -2. The available data on the incidence and prognostic significance of clonal immunoglobulin heavy chain (IgH) gene rearrangements in acute myeloid leukemia (AML) are rather contradictory. The aim of this study was to evaluate the incidence and prognostic significance of RAG-1 and -2 mRNA transcripts and clonal IgH gene rearrangements in a cohort of uniformly treated AML patients; the available literature is also reviewed., Design and Methods: The study was performed on 76 AML patients, newly diagnosed between August 1996 and November 1999. RAG-1/-2 gene expression was analyzed by a reverse transcriptase polymerase chain reaction technique and IgH gene rearrangements were detected with variable region (VH) family-specific and consensus framework region (FWR)-2 and/or-3 primers. Statistical associations were explored between IgH monoclonality/ RAG mRNA expression and: (i) age, gender, FAB subtype, immunophenotype, cytogenetic risk groups; (ii) response variables (response/relapse incidence, survival)., Results: In total, 38/75 samples (50.6%) were RAG-1 and/or -2 positive; 30/76 samples (39.5%) carried clonal IgH genes, whereas 13/30 IgH-positive samples (43.3%) were RAG-1/2-negative. Significant associations were detected only for RAG-2 positivity and unfavorable karyotype and IgH monoclonality and FAB subtypes M4/ M5; no association was identified with response outcome and survival., Interpretation and Conclusions: Lymphoid-specific molecular markers are detected in a significant proportion of AML patients, regardless of differentiation status (assessed morphologically/ immunophenotypically); however, in our experience, they do not seem to constitute an adverse prognostic factor.

Acute promyelocytic leukemia was diagnosed in a 48-year-old man; the karyotype was normal, whereas reverse transcriptase polymerase chain reaction (RT-PCR) analysis identified PML/RAR alpha chimeric transcripts of the bcr3 type. Rather unexpectedly, the patient did not respond to alltrans retinoic acid administration; he attained complete remission with conventional chemotherapy and became PML/RAR alpha negative. Two years later, while PML/RAR alpha negative on RT-PCR, he presented with thrombocytopenia. Bone marrow examination was compatible with myelodysplasia of the RAEB type; the karyotype was normal. Then, after 10 months, he developed overt acute myeloid leukemia with PML/RAR alpha negative, French-American-British M2 blasts; karyotypic analysis revealed mosaicism for trisomy 8.

Cytogenetic analysis was performed in 60 patients with primary myelodysplastic syndromes--diagnosed, treated, and followed in our department. In 41 cases, the presence of the NRAS mutation was also evaluated. The aim of this study was to evaluate the prognostic value of chromosomal abnormalities and NRAS mutation. The median age of the patients was 67 years (18-88 years), and the French-American-British classification was as follows: refractory anemia 26, refractory anemia with ring sideroblasts 4, refractory anemia with excess of blast cells 15, refractory anemia with excess of blast cells in transformation 3, and chronic myelomonocytic leukemia 12. Survival analysis was performed for the patients with a normal (n = 35), an abnormal (n = 25) karyotype and with a single (n = 15) or multiple (n = 10) cytogenetic abnormalities. Abnormal karyotypes were detected in 25 of the 60 patients (41.6%). Fifteen of these patients had a single and 10 had two or more lesions. The median survival of the patients with a normal (33.1 months) and with an abnormal (36.5 months) karyotype was not significantly different. Patients with multiple lesions had a reduced median survival compared with patients with single anomalies (19.2 versus 39.7 months, p = 0.5). Patients with an abnormal karyotype progressed to acute leukemia more frequently compared with patients without lesions (36 versus 28.6%, p = 0.5). NRAS mutation was detected in 2 of 10 CMMoL patients studied and in none of the 31 patients with other types of myelodysplastic syndrome. Marrow blasts more than 10% significantly affected survival.

A caucasian boy with distinct oriental-like facies, short stature, brachydactyly, congenital ventricular septal defect, glaucoma, and speech disorder is reported. Routine laboratory tests, karyotype, and hormonal profile (IGF 1, growth hormone during provocative testing, thyroid hormones, prolactin, gonadotrophins) were normal. Radiologic skeletal survey did not disclose any abnormality. Both parents were apparently normal, but short in stature.

We report a patient with chronic myelogenous leukemia in chronic phase and basophilia which was found to carry a simple variant t(16;22) (q24;q11) Philadelphia (Ph) chromosome in unstimulated bone marrow mononuclear cells. Molecular analysis of peripheral blood and bone marrow mononuclear cells demonstrated the presence of a bcr-abl chimeric mRNA transcript of the b(3) -a(2) type. These findings confirm that band 9q34 participates in the formation of all Ph chromosomes, either standard or variant, even when this is not detectable by conventional cytogenetics. The available literature concerning variant Philadelphia translocations is also reviewed.

Cytogenetic analysis of bone marrow cells from a patient with myelodysplastic syndrome associated with eosinophilia showed a complex translocation with a 46,XY,t(2;18;2)(p23;q11;q32) karyotype. The patient has refractory anemia (RA) according to the French-American-British Cooperative Group (FAB) classification, and after 90 months of follow-up he shows no evidence of leukemic transformation. This chromosomal abnormality has not been previously described in myelodysplastic syndromes and may be associated with good prognosis as the patient has been stable for a long time.

Partial trisomy 17q22-qter is a rare but well-recognized clinical entity. We present a case of partial trisomy for the long arm of chromosome 17, which was detected in a female infant with severe psychomotor and somatic retardation, Stargardt disease, short limbs, and numerous minor anomalies. Differential chromosomal staining demonstrated an excess of genetic material on the long arm of the late replicating X chromosome. FISH and DNA polymorphism analysis showed that the extra material belonged to the distal part of the long arm of chromosome 17 and that there was a partial monosomy of the distal part of the long arm of the derivative X chromosome. The breakpoint regions of this translocation were identified by molecular analysis using polymorphic microsatellite markers on human chromosomes 17 and X. The origin of the abnormal X chromosome was found to be paternal, whereas the origin of the duplicated part of chromosome 17 was maternal. The unbalanced translocation between the paternal X and the maternal chromosome 17 is, therefore, suggested to be due to a postzygotic error.

We report two cases with chronic myeloproliferative disorder which were found to carry simple variant Philadelphia (Ph) t(14;22)(q32;q11) in unstimulated bone marrow mononuclear cells. Both cases were characterized molecularly by Southern blot, reverse transcription-polymerase chain reaction (RT-PCR), and direct sequencing of the RT-PCR products. In the first case (female, aged 65, in blastic transformation which developed one year after the initial diagnosis of myelofibrosis), a t(14;22) (q32;q11) was found in association with several other chromosomal abnormalities [48,XX,+X,+5,del(5) (q12q32),+8,der(9)t(9;11)(q32;q11),-11]; molecular analysis demonstrated the presence of a BCR-ABL chimeric gene and mRNA transcript of the b2-a2 type. In the second case (female, aged 16, with clinical and hematologic features typical of chronic myelogenous leukemia in chronic phase), a t(14;22) (q32;q11) was identified as the sole karyotypic abnormality; again, molecular analysis demonstrated the presence of a BCR-ABL chimeric gene and mRNA transcript, this time of the b3-a2 type. Our findings further support the notion that, even when undetectable by conventional cytogenetics, band 9q34 participates in all Ph chromosomes and leads to the formation of chimeric BCR-ABL genes.

We report a case of chronic myelomonocytic leukemia in which cytogenetic analysis revealed a 47,XY, +1, +der(7)del(7)(q32q36)ins(7;1)(q32;p36.3p22) chromosomal constitution. This abnormal karyotype, which as a whole is new to any myeloid malignancy, points to a possible pathogenetic role for the oncogenes MET and FGR on the derivative chromosome 7, and for the CSF1 and JUN genes flanking the breakpoint on chromosome 1.

Cytogenetic analysis of bone marrow cells from a patient with anemia, marked leukocytosis with eosinophilia, and thrombocytopenia showed monosomy 7 in all metaphases examined. The patient has refractory anemia (RA) according to FAB classification. Because of the hypereosinophilia of the patient, PCR technique was performed and no bcr-abl mRNA, specific for chronic myelogenous leukemia, was detected. Monosomy 7 has not been previously described in cases with hypereosinophilia. We assume, according to previous reports, that multiple genetic lesions can be involved in the pathogenesis of hypereosinophilia in this patient.

In order to investigate the mechanism(s) underlying mosaicism for trisomy 21, we genotyped 17 families with mosaic trisomy 21 probands, using 28 PCR-detectable DNA polymorphic markers that map in the pericentromeric region and long arm of chromosome 21. The percentage of cells with trisomy 21 in the probands' blood lymphocytes was 6%-94%. There were two classes of autoradiographic results: In class I, a "third allele" of lower intensity was detected in the proband's DNA for at least two chromosome 21 markers. The interpretation of this result was that the proband had inherited three chromosomes 21 after meiotic nondisjunction (NDJ) (trisomy 21 zygote) and subsequently lost one because of mitotic (somatic) error, the lost chromosome 21 being that with the lowest-intensity polymorphic allele. The parental origin and the meiotic stage of NDJ could also be determined. In class II, a "third allele" was never detected. In these cases, the mosaicism probably occurred either by a postzygotic, mitotic error in a normal zygote that followed a normal meiosis (class IIA mechanism); by premeiotic, mitotic NDJ yielding an aneusomic zygote after meiosis, and subsequent mitotic loss (class IIB mechanism); or by a meiosis II error with lack of crossover in the preceding meiosis I, followed by mitotic loss after fertilization (class IIC mechanism). Among class II mechanisms, the most likely is mechanism IIA, while IIC is the least likely. There were 10 cases of class I and 7 cases of class II results.(ABSTRACT TRUNCATED AT 250 WORDS)

Uniparental disomy (UPD) involving several different chromosomes has been described in several cases of human pathologies. In order to investigate whether UPD for chromosome 21 is associated with abnormal phenotypes, we analyzed DNA polymorphisms in DNA from a family with de novo Robertsonian translocation t(21q;21q). The proband was a healthy male with 45 dup(21q) who was ascertained through his trisomy 21 offspring. No phenotypic abnormalities were noted in the physical exam, and his past medical history was unremarkable. We obtained genotypes for the proband and his parents' leukocyte DNAs from 17 highly informative short sequence repeat polymorphisms that map in the pericentromeric region and along the entire length of 21q. The order of the markers has been previously determined through the linkage and physical maps of this chromosome. For the nine informative markers there was no maternal allele contribution to the genotype of the proband; in addition, there was always reduction to homozygosity of a paternal allele. These data indicated that there was paternal uniparental isodisomy for chromosome 21 (pUPiD21). We conclude that pUPiD21 is not associated with abnormal phenotypes and that there are probably no imprinted genes on chromosome 21.

Three Down syndrome patients for whom karyotypic analysis showed a "mirror" (reverse tandem) duplication of chromosome 21 were studied by phenotypic, cytogenetic, and molecular methods. On high-resolution R-banding analysis performed in two cases, the size of the fusion 21q22.3 band was apparently less than twice the size of the normal 21q22.3, suggesting a partial deletion of distal 21q. The evaluation of eight chromosome 21 single-copy sequences of the 21q22 region--namely, SOD1, D21S15, D21S42, CRYA1, PFKL, CD18, COL6A1, and S100B--by a slot blot method showed in all three cases a partial deletion of 21q22.3 and partial monosomy. The translocation breakpoints were different in each patient, and in two cases the rearranged chromosome was found to be asymmetrical. The molecular definition of the monosomy 21 in each patient was, respectively, COL6A1-S100B, CD18-S100B, and PFKL-S100B. DNA polymorphism analysis indicated in all cases a homozygosity of the duplicated material. The duplicated region was maternal in two patients and paternal in one patient. These data suggest that the reverse tandem chromosomes did not result from a telomeric fusion between chromosomes 21 but from a translocation between sister chromatids. The phenotypes of these patients did not differ significantly from that of individuals with full trisomy 21, except in one case with large ears with an unfolded helix. The fact that monosomy of distal 21q22.3 in these patients resulted in a phenotype very similar to Down syndrome suggests that the duplication of the genes located in this part of chromosome 21 is not necessary for the pathogenesis of the Down syndrome features observed in these patients, including most of the facial and hand features, muscular hypotonia, cardiopathy of the Fallot tetralogy type, and part of the mental retardation.

We have studied DNA polymorphisms at loci in the pericentromeric region on the long arm of chromosome 21 in 200 families with trisomy 21, in order to determine the meiotic origin of nondisjunction. Maintenance of heterozygosity for parental markers in the individual with trisomy 21 was interpreted as resulting from a meiosis I error, while reduction to homozygosity was attributed to a meiosis II error. Nondisjunction was paternal in 9 cases and was maternal in 188 cases, as reported earlier. Among the 188 maternal cases, nondisjunction occurred in meiosis I in 128 cases and in meiosis II in 38 cases; in 22 cases the DNA markers used were uninformative. Therefore meiosis I was responsible for 77.1% and meiosis II for 22.9% of maternal nondisjunction. Among the 9 paternal nondisjunction cases the error occurred in meiosis I in 2 cases (22.2%) and in meiosis II in 7 (77.8%) cases. Since there was no significant difference in the distribution of maternal ages between maternal I error versus maternal II error, it is unlikely that an error at a particular of maternal ages between maternal I error versus maternal II error, it is unlikely that an error at a particular meiotic stage contributes significantly to the increasing incidence of Down syndrome with advancing maternal age. Although the DNA polymorphisms used were at loci which map close to the centromere, it is likely that rare errors in meiotic-origin assignments may have occurred because of a small number of crossovers between the markers and the centromere.(ABSTRACT TRUNCATED AT 250 WORDS)