INTRODUCTION:Robertsonian translocations resulting from the fusion of two acrocentric chromosomes are the most common chromosomal rearrangements in healthy individuals. Female carriers of a Robertsonian 14;21 translocation have a 10% risk for a liveborn with trisomy 21. METHODS:The study is based on a large family from Oman with eight offspring with translocation trisomy 21 (rob(14;21)(q10;q10),+21). The core family had nine live births, of which five were affected by translocation trisomy 21, two are monozygotic twins. The meiotic recombination pattern was analyzed by microsatellite markers covering chromosomes 21 and 14. For comparison, meiotic recombination was studied in an Arab family with three offspring with trisomy 21. In addition, in the mother of the core family whole-genome sequencing (WGS) was performed to look for possible variants involved in this process. RESULTS:Apart from the core family, there are three other related families with one affected child each. The increased risk for a child with translocation trisomy 21 in the core family is significant. In all cases, the nondisjunction took place at the first meiotic division (MI). Crossovers along chromosome 21 were observed in all affected children, in 2 cases a double crossover in the proximal part of chromosome 21. This pattern is completely different to that of the family with free trisomy 21. WGS did not reveal known pathogenic/likely pathogenic variants related to meiotic dysfunction. CONCLUSION:To the best of our knowledge, such a chromosomal transmission ratio distortion has not been reported so far. In addition, meiotic recombination between the translocation chromosome and free chromosome 21 showed an unusual pattern.

We report on a consanguineous family with two infertile sisters with oocyte arrest and prematurely condensed sperm chromosomes. A genome-wide linkage scan and exome sequencing revealed a homozygous variant in the gene for the thyroid receptor interacting protein 13 (TRIP13), c.518G˃A (p.Arg173Gln), affecting an evolutionary highly conserved amino acid within an ATP binding motif. Just recently, compound heterozygosity for this variant was described in a Chinese proband as pathogenic, confirming that the homozygous mutation is causative for the oocyte arrest. The TRIP13 gene and the orthologous yeast pch2 gene are, amongst others, involved in a meiotic checkpoint control. This checkpoint defect is obviously responsible for the premature condensation of the sperm chromosomes. TRIP13 and pch2 are involved in meiotic recombination. To exclude that it is involved in reciprocal somatic exchanges, we analyzed the rate of sister chromatid exchanges (SCEs) in the proband´s lymphoblastoid cells. Obviously, TRIP13 is not involved in this type of somatic recombination. Moreover, we tested whether TRIP13 can complement the defect of the yeast pch2 gene. Using a yeast deletion strain lacking pch2, we integrated plasmids containing either the yeast pch2 or the human TRIP13 gene, both harboring the wild-type or the mutant allele and assessed the crossingover rate between marker genes lys2 and leu2 as a measure of complementation. Evidence is presented that the human plasmids, unexpectedly also that with the mutation, could complement the pch2 deficient yeast strain, underlining that the evolutionary conservation at the molecular level obviously extends to the functional level.

Trisomy 21 (Down syndrome) is the most common autosomal aneuploidy among newborns. About 90% result from meiotic nondisjunction during oogenesis, which occurs around conception, when also the most profound epigenetic modifications take place. Thus, maternal meiosis is an error prone process with an extreme sensitivity to endogenous factors, as exemplified by maternal age. This contrasts with the missing acceptance of causal exogenous factors. The proof of an environmental agent is a great challenge, both with respect to ascertainment bias, determination of time and dosage of exposure, as well as registration of the relevant individual health data affecting the birth prevalence. Based on a few exemplary epidemiological studies the feasibility of trisomy 21 monitoring is illustrated. In the nearer future the methodical premises will be clearly improved, both due to the establishment of electronic health registers and to the introduction of non-invasive prenatal tests. Down syndrome is a sentinel phenotype, presumably also with regard to other congenital anomalies. Thus, monitoring of trisomy 21 offers new chances for risk avoidance and preventive measures, but also for basic research concerning identification of relevant genomic variants involved in chromosomal nondisjunction.

The evolutionary conserved Polo-like kinase 4 (PLK4) is essential for centriole duplication, spindle assembly, and de novo centriole formation. In man, homozygous mutations in PLK4 lead to primary microcephaly, altered PLK4 expression is associated with aneuploidy in human embryos. Here, we report on a consanguineous four-generation family with 8 affected individuals compound heterozygous for a novel missense variant, c.881 T > G, and a deletion of the PLK4 gene. The clinical phenotype of the adult patients is mild compared to individuals with previously described PLK4 mutations. One individual was homozygous for the variant c.881G and phenotypically unaffected. The deletion was inherited by 14 of 16 offspring and thus exhibits transmission ratio distortion (TRD). Moreover, based on the already published families with PLK4 mutations, it could be shown that due to the preferential transmission of the mutant alleles, the number of affected offspring is significantly increased. It is assumed that reduced expression of PLK4 decreases the intrinsically high error rate of the first cell divisions after fertilization, increases the number of viable embryos and thus leads to preferential transmission of the deleted/mutated alleles.

BACKGROUND:Nibrin, as part of the NBN/MRE11/RAD50 complex, is mutated in Nijmegen breakage syndrome (NBS), which leads to impaired DNA damage response and lymphoid malignancy.RESULTS:Telomere length (TL) was markedly reduced in homozygous patients (and comparably so in all chromosomes) by ~40% (qPCR) and was slightly reduced in NBS heterozygotes older than 30 years (~25% in qPCR), in accordance with the respective cancer rates. Humanized cancer-free NBS mice had normal TL. Telomere elongation was inducible by telomerase and/or alternative telomere lengthening but was associated with abnormal expression of telomeric genes involved in aging and/or cell growth. Lymphoblastoid cells from NBS patients with long survival times (>12 years) displayed the shortest telomeres and low caspase 7 activity.CONCLUSIONS:NBS is a secondary telomeropathy. The two-edged sword of telomere attrition enhances the cancer-prone situation in NBS but can also lead to a relatively stable cellular phenotype in tumor survivors. Results suggest a modular model for progeroid syndromes with abnormal expression of telomeric genes as a molecular basis.METHODS:We studied TL and function in 38 homozygous individuals, 27 heterozygotes, one homozygous fetus, six NBS lymphoblastoid cell lines, and humanized NBS mice, all with the same founder NBN mutation: c.657_661del5.

Chromosomen sind im Zellkern lokalisierte, molekular hochorganisierte Struktureinheiten, die aus DNA, Proteinen und RNA bestehen. Sie sind die Träger der Erbinformation und lassen sich während der Zellteilung (Mitose) lichtmikroskopisch darstellen. Mikroskopische und submikroskopische Chromosomenaberrationen, d. h. chromosomale und segmentale Aneuploidien, z. B. Trisomien, Mikrodeletionen, verursachen komplexe Fehlbildungs- und Dysmorphiesyndrome. Zu den lebensfähigen autosomalen Aneuploidien gehören die Trisomie 21 (Down-Syndrom), 13 (Pätau-Syndrom) und 18 (Edwards-Syndrom). Häufige gonosomale Aneuploidien sind Monosomie X (45,X – Ullrich-Turner-Syndrom), Trisomie X (47,XXX – Triple X) und das Klinefelter-Syndrom (47,XXY). Häufige Mikrodeletionssyndrome sind u. a. DiGeorge-Syndrom und Shprintzen-Syndrom (22q11), Prader-Willi-Syndrom (15q12) und Angelman-Syndrom (15q12), Williams-Beuren-Syndrom (7q11) und Miller-Dieker-Syndrom (17p13). Bei der Labordiagnostik komplexer Syndrome wird die mikroskopische Chromosomenanalyse (Karyogramm; FISH = Fluoreszenz-in-situ-Hybridisierung) durch moderne molekulargenetische Methoden wie DNA-Array-Analyse und Hochdurchsatzsequenzierung (z. B. Exom-Analyse) ergänzt oder ersetzt.

The autosomal recessive genetic disorder Nijmegen breakage syndrome (NBS) is characterized by a defect in DNA double-strand break repair protein nibrin and chromosome instability associated with a high predisposition to cancer. Here we hypothesized that impaired nibrin/MRE11/RAD50 telomere maintenance complex may also affect telomere length and modulate the cancer phenotype. Telomere length was studied in blood from 38 homozygous and 27 heterozygous individuals, in one homozygous fetus, and in sex NBS lymphoblastoid cell lines (all with the founder mutation c.657_661del5), and in three humanized Nbs mice, using qPCR, TRF and Q-FISH. Telomere lengths were markedly but uniformly reduced to 20-40% of healthy controls. There was no correlation between telomere length and severity of clinical phenotype or age of death. By contrast, individual patients with very short telomeres displayed long survival times after cancer manifestation. Mildly accelerated telomere attrition was found in older NBS heterozygotes. In the NBS-fetus, the spinal cord, brain and heart had the longest telomeres, skin the shortest. Humanized Nbs mice (with much longer telo-meres than those in human beings) did not show accelerated telomere attrition. Our data clearly show that NBS is a secondary telomeropathy with unique features. Te- lomere attrition in NBS may cause genetic instability and contribute to the high cancer incidence in NBS. On the other hand, short telomeres may prevent an even worse pheno-type when a tumor has developed. These data may help to understand the high cancer rate in NBS and also the bifunctional role of telomere shortening in cancerogenesis. Author Summary DNA damage is harmful because it leads to mutations in genes that initiate or accelerate cancerogenesis. The devastating consequences of DNA damage are manifested in diseases with non-functional repair pathways such as Nijmegen breakage syndrome (NBS). A common feature of these diseases is a high tumor incidence. However, cancer incidence varies and is not clear why it is highest for NBS. In a previous study, we have shown that the underlying nebrin mutation not only leads to defective DNA repair but also to higher degree of oxidative stress that generates further DNA lesions. Nibrin may play also an important role in protecting chromosome ends, the telomeres, from inap-propriate DNA repair. Therefore we examined the telomere length in NBS and show markedly reduced values in affected patients but not in NBC mice (with much milder phenotype and longer telomeres). Telomere attrition contributes to genetic instability and may thus contribute to the high cancer incidence in NBS. Individual patients with very short telomeres, however, displayed long survival times after cancer manifestation. Thus, short telomeres may also prevent an even worse phenotype when a tumor has developed. These data are fundamental to understanding the high cancer rate in NBS and also the bifunctional role of telomere shortening in cancer.

Nijmegen breakage syndrome is an autosomal recessive disorder characterized by microcephaly, immunodeficiency, hypersensitivity to X-irradiation, and a high predisposition to cancer. Nibrin, the product of the NBN gene, is part of the MRE11/RAD50 (MRN) complex that is involved in the repair of DNA double strand breaks (DSBs), and plays a critical role in the processing of DSBs in immune gene rearrangements, telomere maintenance, and meiotic recombination. NBS skin fibroblasts grow slowly in culture and enter early into senescence.

A substantial number of individuals with Fanconi anemia (FA) develop bone marrow failure and are treated with androgen therapy in order to increase blood counts. The authors retrospectively identified 70 patients who received androgen therapy any time between July 1976 and September 2014. Among these patients, 37 had medical records for analysis. Twenty-five of the 37 (68%) patients had response in hemoglobin level (n = 25), platelet count (n = 21), and/or absolute neutrophil count (n = 13). The median rise in hemoglobin was 6.5mg/dL, platelet count 70,000/mm(3), and absolute neutrophil count (ANC) 1530/mu L. The majority of patients (n = 22) had a response in 2 or more blood parameters. Reasons for discontinuation of therapy included development of cytogenetic aberrations (n = 9), lack of response (n = 7), hepatic adenoma (n = 6), progression to myelodysplastic syndrome/acute myeloid leukemia (n = 3), stabilization of blood parameters (n = 3), resolution of cytopenia secondary to mosaicism (n = 1), virilization (n = 1), development of anogenital carcinoma (n = 1), inaccessibility of medication (n = 1), and unknown (n = 1). Four patients at last follow-up remain on androgen therapy. These results highlight that androgen therapy can significantly improve blood counts for many FA patients, but progression of underlying bone marrow disease and development of liver adenomas requires careful monitoring.

Mutations in the MCPH1 gene result in primary microcephaly in combination with a unique cellular phenotype of defective chromosome condensation. MCPH1 patient cells display premature chromosome condensation in G2 phase of the cell cycle and delayed decondensation in early G1 phase, observable as an increased proportion of cells with prophase-like appearance. MCPH1 deficiency thus appears to uncouple the chromosome cycle from the coordinated series of events that take place during mitosis such as some phases of the centrosome cycle and nuclear envelope breakdown. Here, we provide a further characterization of the effects of MCPH1 loss-of-function on chromosome morphology. In comparison to healthy controls, chromosomes of MCPH1 patients are shorter and display a pronounced coiling of their central chromatid axes. In addition, a substantial fraction of metaphase chromosomes shows apparently unresolved chromatids with twisted appearance. The patient chromosomes also showed signs of defective centromeric cohesion, which become more apparent and pronounced after harsh hypotonic conditions. Taking together, the observed alterations indicate additional so far unknown functions of MCPH1 during chromosome shaping and dynamics.

Two 5-methylcytosine (5-MeC)-rich heterochromatic regions were demonstrated in metaphase chromosomes of the Indian muntjac by indirect immunofluorescence using a monoclonal anti-5-MeC antibody. The metaphases were obtained from diploid and triploid cell lines. A major region is located in the 'neck' of the 3;X fusion chromosome and can be detected after denaturation of the chromosomal DNA with UV-light irradiation for 1 h. It is located exactly at the border of the X chromosome and the translocated autosome 3. A minor region is found in the centromeric region of the free autosome 3 after denaturing the chromosomal DNA for 3 h or longer. The structure and possible function of the major hypermethylated region as barrier against spreading of the X-inactivation process into the autosome 3 is discussed.

Objective The aim of the present study was to assess the risk of major anomalies in the offspring of consanguineous couples, including data on the prenatal situation.Methods Over 20years (1993-2012), 35391 fetuses were examined by prenatal sonography. In 675 cases (1.9%), parents were consanguineous, with 307 couples (45.5%) related as first cousins, 368 couples (54.5%) beyond first cousins. Detailed information was retrieved on 31710 (89.6%) fetuses, (consanguineous 568: 1.8%).Results Overall prevalence of major anomalies among fetuses with non-consanguineous parents was 2.9% (consanguineous, 10.9%; first cousins, 12.4%; beyond first cousins, 6.5%). Adjusting the overall numbers for cases having been referred because of a previous index case, the prevalences were 2.8% (non-consanguineous) and 6.1% (consanguineous) (first cousin, 8.5%; beyond first cousin, 3.9%). Further adjustment for differential rates of trisomic pregnancies indicated 2.0%/5.9% congenital anomalies (non-consanguineous/consanguineous groups), that is, a consanguinity-associated excess of 3.9%, 6.1% in first cousin progeny and 1.9% beyond first cousin.Conclusions The prevalence of major fetal anomalies associated with consanguinity is higher than in evaluations based only on postnatal life. It is important that this information is made available in genetic counselling programmes, especially in multi-ethnic and multi-religious communities, to enable couples to make informed decisions. (c) 2014 John Wiley & Sons, Ltd.

Entry into mitosis is accompanied by dramatic changes in cellular architecture, metabolism and gene expression. Many viruses have evolved cell cycle arrest strategies to prevent mitotic entry, presumably to ensure sustained, uninterrupted viral replication. Here we show for human cytomegalovirus (HCMV) what happens if the viral cell cycle arrest mechanism is disabled and cells engaged in viral replication enter into unscheduled mitosis. We made use of an HCMV mutant that, due to a defective Cyclin A2 binding motif in its UL21a gene product (pUL21a), has lost its ability to down-regulate Cyclin A2 and, therefore, to arrest cells at the G1/S transition. Cyclin A2 up-regulation in infected cells not only triggered the onset of cellular DNA synthesis, but also promoted the accumulation and nuclear translocation of Cyclin B1-CDK1, premature chromatin condensation and mitotic entry. The infected cells were able to enter metaphase as shown by nuclear lamina disassembly and, often irregular, metaphase spindle formation. However, anaphase onset was blocked by the still intact anaphase promoting complex/cyclosome (APC/C) inhibitory function of pUL21a. Remarkably, the essential viral IE2, but not the related chromosome-associated IE1 protein, disappeared upon mitotic entry, suggesting an inherent instability of IE2 under mitotic conditions. Viral DNA synthesis was impaired in mitosis, as demonstrated by the abnormal morphology and strongly reduced BrdU incorporation rates of viral replication compartments. The prolonged metaphase arrest in infected cells coincided with precocious sister chromatid separation and progressive fragmentation of the chromosomal material. We conclude that the Cyclin A2-binding function of pUL21a contributes to the maintenance of a cell cycle state conducive for the completion of the HCMV replication cycle. Unscheduled mitotic entry during the course of the HCMV replication has fatal consequences, leading to abortive infection and cell death.

Kasuistik: Eine 28-jährige 2 g/2 p mit bis zu diesem Zeitpunkt unauffälligem Schwangerschaftsverlauf wurde in 19+2 SSW mit akut aufgetretener, massiver Epistaxis im Rahmen einer hypertensiven Krise (RR 200/120 mmHg) notfallmäßig aufgenommen. Eine NT-Messung bzw. frühe Feindiagnostik war bei der Patientin auf eigenen Wunsch nicht durchgeführt worden. Es erfolgte zunächst die HNO-Vorstellung und Versorgung der Epistaxis sowie die antihypertensive Therapie, worunter sich eine leichte Besserung der Blutdruckwerte auf 150/85 mmHg zeigte. Auf der geburtshilflichen Station erfolgte die Überwachung, Präeklampsiediagnostik sowie die präzise Ultraschalldiagnostik.

Objectives: The currently available methods for rapid prenatal diagnosis of common chromosomal aneuploidies are either Interphase-Fluorescence in Situ Hybridisation (I-FISH) or Quanti- tative Fluorescent Polymerase Chain Reaction (QF-PCR). QF-PCR represents a rapid, high throughput, cost-effective alternative for Interphase-FISH. The objective of the study was to evaluate the performance of QF-PCR, as a molecular-based technique for the detection of chromosome 21, 18 and 13 copy numbers. Study design: A retrospective cohort of 163 samples referred for screening of common chromosomal aneuploidies was blindly tested for chromosome 21, 18 and 13 copy numbers using QF-PCR and the results were compared with those of conventional cytogenetic analysis. Results: QF-PCR demonstrated optimal sensitivity and specificity (100%) for non mosaic trisomies. QF-PCR was able to consistently detect maternal cell contamination and mosaic trisomies when the trisomic cell line was present at an adequate level (23% or more). However, QF-PCR was unable to detect chromosomal rearrangements for which the primers were not designed. Conclusion: QF- PCR proved its superior performance as a molecular-based method for autosomal aneuploidy detection concerning both sensitivity and specificity.

To ascertain the genetic basis of a PNH case without somatic mutations in PIGA, we performed deep next-generation sequencing on all exons of known genes of the GPI-anchor synthesis pathway. We identified a heterozygous germline splice site mutation in PIGT and a somatic 8MB deletion in granulocytes affecting the other copy of PIGT. PIGA is essential for GPI-anchor synthesis whereas PIGT is essential for attachment of preassembled GPI-anchor to proteins. While a single mutation event in the X-chromosomal gene PIGA is known to cause GPI-anchored protein deficiency, two such hits are required in the autosomal gene PIGT. Our data indicate that PNH can occur even in the presence of fully assembled GPI if its transfer to proteins is defective in hematopoietic stem cells. Introduction Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired hemolytic anemia that results from the expansion of hematopoietic stem cells (HSC) that are deficient for glycosylphosphatidylinositol (GPI), a glycolipid moiety that anchors more than a hundred of different proteins to the cell surface. PNH patients were reported to be deficient for an initial step in the GPI-anchor synthesis that is catalyzed by the GPI-GlcNAc transferase and somatic mutations in the X-chromosomal gene PIGA that encodes a subunit of this transferase complex, are regarded as the causative event in the predominant number of PNH cases. However, in a small number of PNH cases with a clear GPI-anchor deficiency no mutations in PIGA have been found. In this work we report about two mutation events, a germline splice site mutation as well as a somatic deletion in PIGT, which is another gene of the GPI-anchor synthesis pathway, that we identified performing next-generation sequencing in a PNH patient with wild-type PIGA.

Autosomal recessive osteopetrosis (ARO, MIM 259700) is a genetically heterogeneous rare skeletal disorder characterized by failure of osteoclast resorption leading to pathologically increased bone density, bone marrow failure, and fractures. In the neuronopathic form neurological complications are especially severe and progressive. An early identification of the underlying genetic defect is imperative for assessment of prognosis and treatment by hematopoietic stem cell transplantation. Here we describe for the first time homozygous microdeletions of different sizes affecting the OSTM1 gene in two unrelated consanguineous families with children suffering from neuronopathic infantile malignant osteopetrosis. Patients showed an exceptionally severe phenotype with variable CNS malformations, seizures, blindness, and deafness. Multi-organ failure due to sepsis led to early death between six weeks and five months of age in spite of intensive care treatment. Analysis of the breakpoints revealed different mechanisms underlying both rearrangements. Microdeletions seem to represent a considerable portion of OSTM1 mutations and should therefore be included in a sufficient diagnostic screening.