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Contains fulltext : 47561.pdf (Publisher’s version ) (Closed access) Small, submicroscopic, genomic deletions and duplications (1 kb to 10 Mb) constitute up to 15% of all mutations underlying human monogenic diseases. Novel genomic technologies such as microarray-based comparative genomic hybridization (array CGH) allow the mapping of genomic copy number alterations at this submicroscopic level, thereby directly linking disease phenotypes to gene dosage alterations. At present, the entire human genome can be scanned for deletions and duplications at over 30,000 loci simultaneously by array CGH ( approximately 100 kb resolution), thus entailing an attractive gene discovery approach for monogenic conditions, in particular those that are associated with reproductive lethality. Here, we review the present and future potential of microarray-based mapping of genes underlying monogenic diseases and discuss our own experience with the identification of the gene for CHARGE syndrome. We expect that, ultimately, genomic copy number scanning of all 250,000 exons in the human genome will enable immediate disease gene discovery in cases exhibiting single exon duplications and/or deletions.

Contains fulltext : 59169.pdf (Publisher’s version ) (Closed access)

Contains fulltext : 51503.pdf (Publisher’s version ) (Closed access) We describe our findings in a 46,XY female with a clinical features of Genitopatellar syndrome (GPS) and confirmed hermaphroditism with ovotestes, and five additional patients with GPS. GPS is a genetic disorder characterized by renal and genital anomalies, joint dislocation, aplastic or hypoplastic and often displaced patellae, minor facial anomalies, and mental retardation. The genital anomalies clearly distinguish GPS from nail-patella syndrome (NPS) that has similar features, but additionally shows hypoplastic finger- and toenails as found in the 46,XY female. In our patients no mutation was found in the coding regions of WNT4, WNT7A, TBX4, and LMX1B. Fluorescent in situ hybridization (FISH) and array-based comparative genome hybridization (aCGH) analysis showed a 3 Mb deletion of LMX1B, NR6A1, and NR5A1 (SF1) in the 46,XY female. This is the first report of a microdeletion causing haploinsuffiency of LMX1B and NR5A1. The deletion of LMX1B is responsible for the knee anomalies and the deletion of NR5A1 likely causes the sex reversal. Cytogenetic analysis of the five additional patients with diagnosed GPS failed to identify a similar microdeletion, or inversion of a potentially regulatory element between the two genes. This suggests that the locus 9q33-9q34 can be excluded for GPS and that the presented case is unique in its combination of GPS and NPS features caused by a microdeletion associated with loss of function of LMX1B and NR5A1.

Contains fulltext : 51726.pdf (Publisher’s version ) (Closed access)

Contains fulltext : 51728.pdf (Publisher’s version ) (Closed access) Partial deletions of the long arm of chromosome 18 lead to variable phenotypes. Common clinical features include a characteristic face, short stature, congenital aural atresia (CAA), abnormalities of the feet, and mental retardation (MR). The presence or absence of these clinical features may depend on the size and position of the deleted region. Conversely, it is also known that patients whose breakpoints are localized within the same chromosome band may exhibit distinct phenotypes. New molecular techniques such as array CGH allow for a more precise determination of breakpoints in cytogenetic syndromes, thus leading to better-defined genotype-phenotype correlations. In order to update the phenotypic map for chromosome 18q deletions, we applied a tiling resolution chromosome 18 array to determine the exact breakpoints in 29 patients with such deletions. Subsequently, we linked the genotype to the patient's phenotype and integrated our results with those previously published. Using this approach, we were able to refine the critical regions for microcephaly (18q21.33), short stature (18q12.1-q12.3, 18q21.1-q21.33, and 18q22.3-q23), white matter disorders and delayed myelination (18q22.3-q23), growth hormone insufficiency (18q22.3-q23), and CAA (18q22.3). Additionally, the overall level of MR appeared to be mild in patients with deletions distal to 18q21.33 and severe in patients with deletions proximal to 18q21.31. The critical region for the 'typical' 18q-phenotype is a region of 4.3 Mb located within 18q22.3-q23. Molecular characterization of more patients will ultimately lead to a further delineation of the critical regions and thus to the identification of candidate genes for these specific traits.

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Contains fulltext : 50625.pdf (Publisher’s version ) (Closed access)

Contains fulltext : 30198_molekabya.pdf (Publisher’s version ) (Open Access) Chromosomal rearrangements can lead to various serious clinical manifestations, including mental retardation and congenital malformation syndromes. Chromosomal rearrangements larger than 5-10 Mb in size can be detected by conventional karyotyping. A considerable number of clinical disorders, however, is caused by submicroscopic chromosomal rearrangements smaller than 5-10 Mb in size. To routinely detect these rearrangements, an efficient and robust genome-wide technology is needed. One such technology is array-based comparative genomic hybridization (array CGH), an approach which is also referred to as molecular karyotyping. In analogy to the application of array CGH in cancer research, we reasoned that this technology might also be suited for the detection of submicroscopic chromosomal rearrangements in patients with unexplained mental retardation and/or congenital malformation syndromes. The specific aim of this thesis was to explore the feasibility of the array CGH technology for the delineation of DNA copy number alterations for applied clinical genetic and basic genome research purposes. During the course of the project, the concept of molecular karyotyping rapidly changed the field of clinical genetics and genome research and, without any doubt, will continue to do so in the years to come. In case of clinical genetics, we conclude that molecular karyotyping has led to a significant increase in the diagnostic yield in patients with unexplained mental retardation and/or malformation syndromes; the identification of a gene underlying CHARGE syndrome, and the identification of a novel microdeletion syndrome involving chromosome 17q21.31. In case of genome research, we conclude that molecular karyotyping has led to novel insight into the occurrence of copy number variation within the human genome, and into the recombination mechanisms and genomic architectural features underlying the occurrence of copy number variation. Based on the above, we conclude that molecular karyotyping serves as a powerful tool for linking gene dosage alterations to (disease) phenotypes RU Radboud Universiteit Nijmegen, 13 september 2007 Promotor : Geurts van Kessel, A.H.M. Co-promotor : Veltman, J.A. 192 p.