van Eijsden RG, Gerards M, Eijssen LM, Hendrickx AT, Jongbloed RJ, Wokke JH, Hintzen RQ, Rubio-Gozalbo ME, De Coo IF, Briem E, Tiranti V, Smeets HJ. Chip-based mtDNA mutation screening enables fast and reliable genetic diagnosis of OXPHOS patients. Genet Med. 2006 Oct;8(10):620-627.

Gielen M, Lindsey PJ, Derom C, Loos RJ, Derom R, Nijhuis JG, Vlietinck R. Curves of placental weights of live-born twins. Twin Res Hum Genet. 2006 Oct;9(5):664-72.


Speybroeck, N., Lindsey,P.J., Billiouw,M., Madder, M., Lindsey, J.K. and Berkvens, D.L.(2006) Modeling diapause termination of Rhipicephalus appendiculatus using statistical tools to detect sudden behavioral changes and time dependencies. Environmental and Ecological Statistics 2006;13,69-87. 

 

Koolen DA, Herbergs J, Veltman JA, Pfundt R, van Bokhoven H, Stroink H, Sistermans EA, Brunner HG, Geurts van Kessel A, de Vries BB.  Holoprosencephaly and preaxial polydactyly associated with a 1.24 Mb duplication encompassing FBXW11 at 5q35.1. J Hum Genet. 2006 Jul 25: 51(8): 721-6

 

van den Bosch BJ, Lindsey PJ, van den Burg CM, van der Vlies SA, Lips DJ, van der Vusse GJ, Ayoubi TA, Doevendans PA, Smeets HJ. Early and transient gene expression changes in pressure overload-induced cardiac hypertrophy in mice. Genomics 2006 Oct;88(4):480-8

 

Schreuder AH, de Die-Smulders CE, Herbergs J, Koehler PJ. From gene to disease; the PABN1 gene and oculopharyngeal muscular dystrophy. Ned Tijdschr Geneeskd. 2006 May 20;150(20):1124-6

 

Kellen E, Zeegers M, Paulussen A, Van Dongen M, Buntinx F. Fruit consumption reduces the effect of smoking on bladder cancer risk. The Belgian case control study on bladder cancer. Int J Cancer 2006 May 15;118(10):2572-8 SCI 4.375 

 

Romano A, Lindsey PJ, Fischer DC, Delvoux B, Paulussen AD, Janssen RG, Kieback DG. Two functionally relevant polymorphisms in the human progesterone receptor gene (+331 G/A and progins) and the predisposition for breast and/or ovarian cancer. Gynecol Oncoll 2006 May;101(2):287-95 . SCI 2.341 

van Haaften RI, Schroen B, Janssen BJ, van Erk A, Debets JJ, Smeets HJ, Smits JF, van den Wijngaard A, Pinto YM, Evelo CT. Biologically relevant effects of mRNA amplification on gene expression profiles. BMC Bioinformatics. 2006 Apr 11;7(1):200. SCI 5.42

 

Spruijt L, Kolbach DN, de Coo RF, Plomp AS, Bauer NJ, Smeets HJ, de Die-Smulders CE.  Influence of mutation type on clinical expression of leber hereditary optic neuropathy. Am J Ophthalmol. 2006 Apr;141(4):676-682

 

Bijnens AP, Lutgens E, Ayoubi T, Kuiper J, Horrevoets AJ, Daemen MJ. Genome-Wide Expression Studies of Atherosclerosis. Critical Issues in Methodology, Analysis, and Interpretation of Transcriptomics Data. Arterioscler Thromb Vasc Biol.  2006 Jun;26(6):1226-35

 

van Tintelen JP, Entius MM, Bhuiyan ZA, Jongbloed R, Wiesfeld AC, Wilde AA, van der Smagt J, Boven LG, Mannens MM, van Langen IM, Hofstra RM, Otterspoor LC, Doevendans PA, Rodriguez LM, van Gelder IC, Hauer RN. Plakophilin-2 Mutations Are the Major Determinant of Familial Arrhythmogenic Right Ventricular Dysplasia/Cardiomyopathy. Circulation 2006 Apr 4;113(13):1650-8

 

Kellen E, Zeegers M, Paulussen A, Vlietinck R, Vlem EV, Veulemans H, Buntinx F. Does occupational exposure to PAHs, diesel and aromatic amines interact with smoking and metabolic genetic polymorphisms to increase the risk on bladder cancer?; The Belgian case control study on bladder cancer risk. Cancer Lett 2006 May 15;118(10):2572-8

 

Defoor J, Vanhees L, Martens K, Matthijs G, Van Vlerken A, Zielinska D, Schepers D, Vlietinck R, Fagard R. The CAREGENE study: ACE Gene I/D polymorphism and effect of physical training on aerobic power in coronary artery disease. Heart 2006 Apr;92(4):527-8. SCI 3.160 

Shiri-Sverdlov R, Custers A, van Vliet-Ostaptchouk JV, van Gorp PJ, Lindsey PJ, van Tilburg JH, Zhernakova S, Feskens EJ, van der A DL, Dolle ME, van Haeften TW, Koeleman BP, Hofker MH, Wijmenga C. Identification of TUB as a Novel Candidate Gene Influencing Body Weight in Humans. Diabetes. 2006 Feb;55(2):385-9

 

Koopmann TT, Alders M, Jongbloed RJ, Guerrero S, Mannens MM, Wilde AA, Bezzina CR. Long QT syndrome caused by a large duplication in the KCNH2 (HERG) gene undetectable by current polymerase chain reaction-based exon-scanning methodologies. Heart Rhythm. 2006 Jan;3(1):52-5 SCI      

 

 

 

POSTERS

 

ESHG

Symposium S14. Heart disease – congenital and developmental Chair: S. Lyonnet, B. Smeets

SIX3, ZIC2 and SHH mutations in a series of holoprosencephaly patients.
J. Herbergs, D. Tserpelis, S. Spierts, H. Smeets; Academic Hospital Maastricht, Maastricht, The Netherlands. Holoprosencephaly (HPE) is a common severe malformation of the brain that involves abnormal formation and septation of the developing central nervous system. The prevalence is 1:250 during early embryogenesis, but the live born prevalence is only 1:16000. The etiology of HPE is extremely heterogeneous and can include both a teratogenic and/or genetic basis. We studied four genes known to be involved in HPE, namely SHH, ZIC2, SIX3 and TGIF by sequence analysis. A series of in total 47 sporadic and familial HPE cases with a variable clinical spectrum has been analysed. We detected 10 pathogenic mutations (21%), 5 out of 40 sporadic cases (13%) and 5 out of 7 familial cases (71%). One of the familial cases was caused by a mutation in parental germ cells. Four mutations were detected in the SIX3 gene, four mutations in the ZIC2 gene and two mutations in the SHH gene. The familial mutations displayed great phenotypic heterogeneity of the disease, which makes it difficult to establish genotype-phenotype correlations. This phenotypic variability may be due both to environmental factors and to potential modifier genes. HPE development is probably a multihit process , which implicates more genes. This illustrates the importance of further identification of new genes.

Melas in families
S. G. M. Frints1,2, C. E. de Die-Smulders1,2, C. G. Faber3, J. W. Weber3, A. C. Kruseman4, G. M. de Wert5, H. J. M. Smeets6,2; 1Department of Clinical Genetics, University Hospital Maastricht, The Netherlands, 2GROW, University of Maastricht, The Netherlands, 3Department of Neurology, University Hospital Maastricht, The Netherlands, 4Department of Internal Medicine, University Hospital Maastricht, The Netherlands, 5Department of Ethics and Phylosophy, University of Maastricht, The Netherlands, 6Department of Genetics and Cell Biology, University of Maastricht, The Netherlands. Mitochondrial Myopathy, Encephalopathy, Lactic Acidosis, and Strokelike episodes (MELAS/OMIM #540000) syndrome is a relatively frequent mitochondrial disorder. It is a multisystemic disorder with an extremely variable clinical phenotype and can be caused by different mutations in the mitochondrial DNA. The classical A3243G mutation in the MTTL1 (tRNA for leucine (UUR)) gene is most common. We present the clinical features and molecular findings in five families with a mtDNA A3243G mutation. The clinical phenotype in families A, B and C was characterized by proximal muscle weakness, ptosis, external ophthalmoplegia, retinitis pigmentosa, hearing loss and diabetes mellitus. One patient died of heart failure (cardiomyopathy) and one had tachycardia in early adulthood. Family D presented with maternally inherited diabetes mellitus. The first sign in family E was severe hypotonia, developmental delay, muscle weakness, poor growth and elevated lactate in early childhood accompanied by external ophthalmoplegia. Investigation of the A3243G mutation in blood, muscle, hair roots and urine sediment was necessary for diagnosis in patients with nearly no complains. There was no strong correlation between the clinical picture and proportion of mutated mtDNA in these families. Clinical manifestations in MELAS usually become evident when a threshold percentage of mtDNA is mutated, but is not simply a direct consequence of the relative abundance of mutated mtDNA. Other factors such as nuclear background might contribute to the phenotype. Although ethical considerations are being made, preimplantation genetic diagnosis could be an option for few patients with low mutation load in blood and muscle.

Gene expression changes in skeletal muscle from MELAS patients
R. G. E. van Eijsden1,2, L. M. T. Eijssen1, C. M. M. van den Burg1,2, P. J. Lindsey1, W. Sluiter3, K. Schoonderwoerd3, H. R. Scholte3, I. F. M. de Coo4, M. E. Rubio-Gozalbo5, H. J. M. Smeets1,2; 1Department of Genetics and Cell Biology, Genome Centre, Maastricht University, Maastricht, The Netherlands, 2Research Institute GROW, Maastricht University, Maastricht, The Netherlands, 3Department of Biochemistry, Erasmus MC, Rotterdam, The Netherlands, 4Department of Neurology, Erasmus MC, Rotterdam, The Netherlands, 5Department of Paediatrics and Laboratory Genetic Metabolic Diseases, Maastricht University Hospital, Maastricht, The Netherlands. Mitochondrial encephalomyopathies are genetically and clinically heterogeneous disorders. Mutations in different genes can lead to similar syndromes; in contrast, one single mutation can result in a variable clinical manifestation. The most frequent cause (80%) of Mitochondrial Myopathy, Encephalopathy, Lactic Acidosis and Stroke-like episodes (MELAS) is the m.3243A>G point mutation in the mitochondrial tRNALeu(UUR) gene. Other clinical manifestations of this mutation are diabetes, deafness, renal tubulopathy and cardiomyopathy. To explain the differences in pathology observed in carriers of the m.3243A>G mutation, we applied global gene expression profiling on muscle biopsies from affected and unaffected mutation carriers with different levels of the mutation and controls. Protein turnover and reactive oxygen species (ROS) defence were significantly up-regulated pathways and changes were more prominent in the unaffected group with lower mutation levels than in the affected group. Increased production of ROS between m.3243A>G mutation carriers and controls was further demonstrated by dihydroethidium (DHE) staining of superoxide radicals in muscle. We hypothesise that the accumulation of oxidative protein damage due to excessive ROS production stimulates protein turnover. Apparently, this process is more effective at lower mutation levels where the increased ROS production can be dealt with by increasing the expression of genes involved in protein breakdown and protein synthesis, preventing severe symptoms from occurring. If mutation levels get too high, compensation is no longer possible and severe symptoms become manifest.

Mutations in the ND5 subunit of complex I of the mtDNA are a frequent cause of OXPHOS disease
M. J. Blok1, L. Spruijt2,3, R. F. M. de Coo4, K. Schoonderwoerd5, A. Hendrickx1, H. J. Smeets1,2; 1Department of Clinical Genetics, University Hospital Maastricht, Maastricht, The Netherlands, 2Department of Genetics and Cell Biology, University of Maastricht, Maastricht, The Netherlands, 3Research Institute Growth & Development, University of Maastricht, Maastricht, The Netherlands, 4Department of Child Neurology, Erasmus Medical Centre Rotterdam, Rotterdam, The Netherlands, 5Department of Biochemistry, Erasmus Medical Centre Rotterdam, Rotterdam, The Netherlands. Objective: To determine the frequency of mutations in the mitochondrial (MT)-ND5 gene in patients with OXPHOS disease. Background: Mutation detection in the mitochondrial genome is usually limited to common mutations and the tRNA genes. However, mutations in the ND subunits of complex I can be an important cause of OXPHOS disease. Methods: mutation screening of the mtDNA was performed by DHPLC-analysis of120 patients with a mitochondrial disorder. Heteroplasmy levels in different tissues were determined using PCR with fluorescently labelled primers and mutation specific restriction enzymes. Results: We found a MT-ND5 mutation in 3,3% of the patients. Two mutations were new and two have been previously reported. The 13513G>A mutation, associated with MELAS and MELAS/Leigh/ Leber hereditary optic neuropathy overlap syndrome, was found in a relative low percentage in two patients, one with a Leigh and one with a MELAS phenotype. The 13042G>A, once detected in a patient with a MELAS/MERRF phenotype, was now found in a patient with a Leigh-like/NARP phenotype. A new mtDNA mutation (12622G>A) was identified in three brothers, all with infantile encephalopathy (Leigh syndrome) fatal within the first 15 days of life and a novel point mutation (13511A>T) occurred in a patient with a Leigh-like syndrome. Conclusions: Mutation screening of the mitochondrial ND5 gene is advised for routine diagnostics of patients with OXPHOS disease, especially MELAS- and Leigh-like patients.

Compound heterozygosity for mutations in LMNA causes a progeria syndrome without prelamin A accumulation
V. L. R. M. Verstraeten1, J. L. V. Broers2, M. A. M. van Steensel1, S. Zinn- Justin3, F. C. S. Ramaekers2, P. M. Steijlen1, M. Kamps1, H. J. H. Kuijpers2, D. Merckx4, H. J. M. Smeets4, R. C. M. Hennekam5, C. L. M. Marcelis6, A. van den Wijngaard4; 1Department of Dermatology, Maastricht, The Netherlands, 2Department of Molecular Cell Biology, Maastricht, The Netherlands, 3Département d’Ingénierie et d’Etudes des Protéines, Gif-sur-Yvette, France, 4Department of Clinical Genetics, Maastricht, The Netherlands, 5Institute of Child Health, London, United Kingdom, 6Department of Clinical Genetics, Nijmegen, The Netherlands. LMNA-associated progeroid syndromes have been reported with both recessive and dominant inheritance. We report a two-year-old boy with an apparently typical Hutchinson-Gilford progeria syndrome (HGPS) due to compound heterozygous missense mutations in LMNA resulting in T528M and M540T. Both mutations affect a conserved region within the C-terminal globular domain of A-type lamins, shown to be affected in other progeria-like patients. The nuclei of our patient showed no prelamin A accumulation, nor did the dysmorphic nuclei reveal the lobulation typical for HGPS. Instead, nuclear blebs with reduced/ absent expression of B-type lamins as well as honeycomb figures could be detected. The healthy heterozygous parents showed similar nuclear changes, though in a smaller percentage of nuclei. Treatment with a farnesyltransferase inhibitor to block the prelamin A processing resulted in accumulation of prelamin A and improved the nuclear phenotype. In conclusion, these findings suggest a critical role for the affected lamin A/C region in nuclear structure and support a major contribution of abnormal polymerisation to the progeroid phenotype. Prelamin A accumulation may not be the major determinant of the progeroid phenotype, in contrast to earlier suggestions.

High-throughput and comprehensive CHIP-based resequencing of the mitochondrial DNA in patients with OXPHOS disease H. J. M. Smeets1,2, R. Van Eijsden1,2, M. Gerards1,2, A. Hendrickx1, P. Lindsey1, R. De Coo3; 1Genetics and Cell Biology, University Maastricht, Maastricht, The Netherlands, 2Research Institute GROW, Maastricht, The Netherlands, 3Neurology, Erasmus University Medical Center, Rotterdam, The Netherlands. Mitochondrial disorders are often fatal multisystem disorders, associated with abnormalities of oxidative phosphorylation (OXPHOS). Because of its dual genetic control, defects in OXPHOS can be due to mutations in either the mitochondrial (mtDNA) or nuclear DNA. Although OXPHOS disorders have common characteristics, there is considerable clinical variability among patients, even in those having the same genetic defect. Also, clinically indiscernible conditions can be caused by different mutations in a number of genes. Therefore, we applied a new CHIP-based platform for rapid resequencing of the mtDNA. We found a complete match with classical resequencing in 3 samples. Two samples were mixed to generate artificially heteroplasmy at 11 positions in the mtDNA sequence. Ten were detectable as such and one gave a no-call. Analysis of mixed amounts of different mtDNAs indicated that a mutation load of ≥10% should be detectable. Although the platform is not optimal for the detection of small deletions or insertions, we were able to identify two samples with a single nucleotide insertion as a heterozygote call. Screening of 20 patients suspected for mitochondrial disease revealed 171 different mutations: 90 SNPs, 5 known pathogenic mutations and 71 unknown variants (5 of which were heteroplasmic). Our conclusion is that the resequencing CHIPs are a very promising tool for rapid and comprehensive mtDNAscreening. Especially for genomes like the mtDNA, where it is possible to generate the template with a single PCR, and in which the vast majority of the point mutations are nucleotide substitutions, it will become the method of choice.

Fanconi anemia FANCD1/BRCA2 displays genotypic/ phenotypic correlations: a report of two pedigrees and review of the literature.
E. B. Gomez Garcia1, J. de Winter2, M. Macville1, M. J. Blok1, M. Vreeburg1, D. Marcus-Soekarman1, C. E. M. de Die-Smulders1; 1Dept. Clinical Genetics, Maastricht, The Netherlands, 2Dept. of Clinical Genetics and Human Genetics, Free university Medical center, Amsterdam, The Netherlands. Patient 1 had small stature, microcephaly, microphthalmy, cleft palate, VSD, imperforate anus, rectovaginal fistula, absence/hypoplastic thumbs and hypothyroidism. She died at age 3 of a solid tumor in the posterior fossa. Chromosome and complementation studies made the diagnosis of FA type D1. DNA-analysis, reported by Howlett et al. Science 2002, revealed biallelic mutations in the BRCA2 gene: 7699 insAT and 9900 insA as the cause of type D1 in this kindred (EUFA423). Each parent was carrier. Her deceased paternal grandmother was the only relative with cancer (BRCA2 mutation was absent in the pancreatic tumor). Patient 2 developed a Wilms’ tumor at age 1. She had small stature, microcephaly and café au lait spots. A BRCA2 mutation (886 del GT) had been found in her mother, counseled for familial breast cancer (BC). In her father’s family several women had BC, a 9345G>A BRCA2 mutation, reported to have an effect on splicing, was present. Both were present in the child which, together with an increased chromosome breakage, confirmed the diagnosis. Complementation studies are underway. Twenty two other children have been reported. Distinct clinical features from the 24 patients with FANCD1/BRCA2 are: high incidence of solid tumors in early childhood,10 patients had brain tumors and six a Wilms’ tumor, absence of aplastic anemia, early onset acute leukemia, imperforate anus and BC among relatives. Little correlation between FA complementation groups and clinical features had been reported so far, here we show that genotype/ phenotype associations do exist for this subtype, with potential important therapeutic implications.

ASHG

Mutations in the ND5 subunit of complex I of the mtDNA are a frequent cause of OXPHOS disease.
M.J. Blok1, L. Spruijt2, I.F.M. DeCoo3, K. Schoonderwoerd3, A. Hendrickx1, H.J.M. Smeets1,2 1) Clinical genetics, Academic Hospital Maastricht, Maastricht, Netherlands; 2) Department of Genetics and Cell Biology and Research Institute Growth & Development (GROW), University of Maastricht, the Netherlands; 3) Department of Child Neurology, Department of Clinical Genetics, Erasmus Medical Centre Rotterdam, the Netherlands.
Objective: To investigate if regions in the mtDNA are preferentially mutated in patients with OXPHOS disease. Background: Mutation detection in the mitochondrial genome is usually limited to common mutations and the tRNA genes. However, mutations in other mtDNA regions can be an important cause of OXPHOS disease as well. Methods: Screening of the mtDNA for heteroplasmic mutations was performed by DHPLC-analysis of 116 patients with OXPHOS disease but without the common mtDNA mutations. Heteroplasmy levels in different tissues were determined using PCR with fluorescently labeled primers and mutation specific restriction enzymes. Results: A mtDNA mutation was detected in 15 patients, five of which were present in the ND5 gene. Two mutations were new and two were known, one of which was found twice. The novel mtDNA point mutation, 12622G>A, was identified in three brothers, all with infantile encephalopathy (Leigh syndrome) fatal within the first 15 days of life. The other novel point mutation, 13511A>T, occurred in a patient with a Leigh-like syndrome. The known 13513G>A mutation, associated with MELAS and MELAS/Leigh/Leber hereditary optic neuropathy overlap syndrome, was found in a relative low percentage in two patients from two different families, one with a MELAS/Leigh and one with a MELAS/CPEO phenotype. The 13042G>A mutation, once detected in a patient with a MELAS/MERRF phenotype, was now found in a patient with a Leigh-like phenotype. Conclusions: Mutation screening of the ND5 gene is advised for routine diagnostics of patients with OXPHOS disease, especially MELAS- and Leigh(-like) patients.

SIX3, ZIC2 and SHH mutations in a series of holoprosencephaly patients.
J. Herbergs, S. Spierts, D. Tserpelis, H. Smeets Dept Clinical Genetics, Academic Hosp Maastricht, Maastricht, Netherlands. Holoprosencephaly (HPE) is a common severe malformation of the brain that involves abnormal formation and septation of the developing central nervous system. The prevalence is 1:250 during early embryogenesis, but the live born prevalence is only 1:16000. The etiology of HPE is extremely heterogeneous and can include both a teratogenic and/or genetic basis. We studied four genes known to be involved in HPE, namely SHH, ZIC2, SIX3 and TGIF by sequence analysis. A series of in total 48 sporadic and familial HPE cases with a variable clinical spectrum has been analysed. We detected 12 pathogenic mutations (25%), 4 out of 39 sporadic cases (10%) and 7 out of 9 familial cases (78%). One of the familial cases was caused by a mutation in parental germ cells. Seven mutations were detected in the SIX3 gene, three mutations in the ZIC2 gene and two mutations in the SHH gene. The familial mutations displayed great phenotypic heterogeneity of the disease, which makes it difficult to establish genotype-phenotype correlations. This phenotypic variability may be due both to environmental factors and to potential modifier genes. HPE development is probably a multihit process , which implicates more genes; illustrating the importance of further identification of new genes.

mtDNA point mutations are present at various levels of heteroplasmy in human oocytes.
L.J.A.M. Jacobs1,2, M. Gerards1,2, P.F. Chinnery3, J.C.M. Dumoulin2, 4, J.P.M. Geraedts1,2, H.J.M. Smeets1, 2 1) Genetics and Cell Biology, University of Maastricht, Maastricht, Netherlands; 2) Research institute GROW, University of Maastricht, Maastricht, The Netherlands; 3) Mitochondrial Research Group, University of Newcastle upon Tyne, Newcastle upon Tyne, UK; 4) Department of IVF, Academic Hospital Maastricht, Maastricht, The Netherlands. Little is known about the load of mutations and polymorphisms in the mtDNA of human oocytes and the possible effect these mutations may have during life. To investigate this, we optimised at the single cell level the recently developed method to screen the entire mtDNA for mainly heteroplasmic mutations by denaturing high performance liquid chromatography (DHPLC) analysis. This method is sensitive (~1% heteroplasmy detectable), specific and rapid. The entire mtDNA of 26 oocytes of 13 women was screened by this method. Ten different heteroplasmic mutations, of which only one was located in the D-loop and of which two were observed twice, were detected in seven oocytes with mutation loads ranging from less than 5% to 50%. From 8 women more than one oocyte was received and in four of them heteroplasmic differences between oocytes of the same woman were observed. In one of these four also two homoplasmic D-loop variants were detected. Additionally, four oocytes of a single woman were sequenced using the MitoChip (which lacks the D-loop region), but all sequences were identical. It is concluded that heteroplasmic mtDNA mutations are common in oocytes and that depending on the position and mutation load they might give rise to OXPHOS disease early or later in life.

Evaluation and validation of Preimplantation Genetic Diagnosis (PGD) by PCR analysis: comparison of the blastomere and corresponding embryo genotype.
J. Dreesen1,3, M. Drüsedau1, H. Smeets1,3, C. De Die-Smulders1, J. Dumoulin2, J. Evers2, J. Geraedts1,3, J. Herbergs1,3 1) Depts. Clinical Genetics; 2) Obstetrics & Gynaecology, Academic Hospital Maastricht; 3) GROW, Maastricht University, Maastricht, The Netherlands. PGD can be an alternative for prenatal diagnosis for couples at high risk of a monogenic disorder. Unaffected embryos, genotyped by analysis of biopsied blastomeres, are selected for embryo transfer (ET). The aim of the present study is to validate the PGD-PCR procedure, and determine the diagnostic value. PCR analysis of embryos not selected for ET and unsuitable for cryopreservation after PGD were used as golden standard. According to embryo morphology quality scores, embryos on day 4 post fertilization (day ET) were divided into class 1-4, with class 4 being the lowest embryo morphology score. The genotype from the biopsied blastomere and the corresponding embryo were compared. To establish the validity of PGD-PCR procedure, sensitivity(Se), specificity(Sp), and Likelihood Ratio (LR) were calculated for the total, class 4 excluded and class 4 embryo group. For the diagnostic value, Positive- (PPV) and Negative Predictive Value (NPV) were calculated. In our centre 80 women underwent PGD-PCR, resulting in 793 embryo genotypes, 241 unaffected embryos were used for ET. From 447 embryos the blastomere genotype has been compared with the reanalysed embryo genotype. PGD-PCR blastomere outcome, scored as affected or aberrant in 234/241 positive embryos (Se; 97,1%), and scored unaffected in 181/206 negative embryos (Sp: 87,9%). Out of the 7 false negative embryos, 6 were graded as class 4. The Se in the class 4 embryo group was 90,2% (55/61) and Sp 93,2% (41/44). Exclusion of class 4 embryos resulted in a Se of 99,4% (179/180), a Sp of 86,4% (140/162) and a LR positive test of 7.3 and LR negative test of 0.006. The PPV of an abnormal PGD-PCR is 89.1%, the NPV of a normal PGD-PCR is 99.3% in this group. PGD-PCR procedure is validated as a diagnostically reliable method for selecting unaffected embryos for ET. Accuracy of PGD-PCR analysis improves by rejecting class 4 embryos for ET.

Modeling of twin growth during gestation and quantification of the genetic and environmental factors involved.
M. Gielen1,2, P.J. Lindsey1,2, C. Derom3, H.J.M. Smeets1, R. Derom3, J.G. Nijhuis4 1) Population Genetics, Genomics and Bioinformatics, Maastricht University, Maastricht, Netherlands; 2) NUTRIM, Maastricht University, Maastricht, the Netherlands; 3) Human Genetics, Faculty of Medicine, Catholic University of Leuven, Leuven, Belgium; 4) Obstetrics and Gynecology, University Hospital Maastricht, Maastricht, The Netherlands. Structural equation modeling of birth weight has given inconsistent results with heritability estimates between 10 and 40%. One explanation could be that the heritability changes during gestational age or that different covariates explain different parts of the variance covariance structure. The aim of this study was to model prenatal growth as well as to quantify the genetic and environmental components to explain the effects of several covariates. Perinatal data were obtained from 4232 live-born twin pairs from the East Flanders Prospective Twin Survey, Belgium. Heritability of birth weights at different gestational ages was estimated using a non-linear multivariate Gaussian regression with covariates in the mean model as well as in the variance and the covariance components. Following covariates were considered: gestational age, sex, chorionicity, placental type, insertion of the umbilical cord, birth order, the origin of the pregnancy (spontaneous, in-vitro-fertilization, induction of ovulation), maternal age, parity, and neonatal death. During gestation, heritability dropped from 37% at 25 weeks to 14% at 42 weeks. After adjusting for covariates the heritability increased: from 58% at 25 weeks to 26% at 42 weeks. The origin of the pregnancy did not contribute to the model. Chorionicity explained part of prenatal growth but had almost no influence on the covariance structure. All other covariates influenced the genetic and environmental components of the covariance structure in different ways. For complex traits such as growth, it is important to explain a large part of the variance and covariance, as it will help to find genes in linkage and association studies. Thus, explaining (birth) weight by modeling the genetic and environmental factors gives a better inside in factors influencing growth during gestation.