Jean-Pierre Fryns

What next for preimplantation genetic screening? High mitotic chromosome instability rate provides the biological basis for the low success rate

Preimplantation genetic screening is being scrutinized, as recent randomized clinical trials failed to observe the expected significant increase in live birth rates following fluorescence in situ hybridization (FISH)-based screening. Although these randomized clinical trials are criticized on their design, skills or premature stop, it is generally believed that well-designed and well-executed randomized clinical trials would resolve the debate about the potential benefit of preimplantation genetic screening. Since FISH can analyze only a limited number of chromosomal loci, some of the embryos transferred might be diagnosed as ‘normal’ but in fact be aneuploid for one or more chromosomes not tested. Hence, genome-wide array comparative genome hybridization screening enabling aneuploidy detection of all chromosomes was thought to be a first step toward a better design. We recently showed array screening indeed enables accurate determination of the copy number state of all chromosomes in a single cell. Surprisingly, however, this genome-wide array screening revealed a much higher frequency and complexity of chromosomal aberrations in early embryos than anticipated, with imbalances in a staggering 90% of all embryos. The mitotic error rate in cleavage stage embryos was proven to be higher than the meiotic aneuploidy rate and as a consequence, the genome of a single blastomere is not representative for the genome of the other cells of the embryo. Hence, potentially viable embryos will be discarded upon screening a single blastomere. This observation provides a biological basis for the failure of the randomized clinical trials to increase baby-take-home rates using FISH on cleavage stage embroys.

HEREDITARY RENAL ADYSPLASIA: New Observations and Hypotheses

Renal agenesis and dysplasia are frequently regarded by pathologists, even pediatric pathologists, as sporadic malformations. We report six fetal autopsy cases of hereditary renal adysplasia (HRA): two pairs of siblings, one case with paternal unilateral renal agenesis, and one case with an autosomal balanced 6p/19q translocation. The main purpose of this paper is to emphasize that nonsyndromal renal agenesis and dysplasia are pathogenetically related and often inherited as an autosomal dominant trait with incomplete penetrance and variable expression. A subsidiary purpose is to present a case of bilateral multicystic dysplasia with a balanced 6p/19q translocation. This observation further supports the assignment of one of the loci for HRA to chromosome 6p.

Distal limb deficiencies, micrognathia syndrome, and syndromic forms of split hand foot malformation (SHFM) are caused by chromosome 10q genomic rearrangements

Background The 10q24 chromosomal region has previously been implicated in split hand foot malformation (SHFM). SHFM3 was mapped to a large interval on chromosome 10q. The corresponding dactylaplasia mouse model was linked to the syntenic locus on chromosome 19. It was shown that the two existing Dac alleles result from MusD-insertions upstream of or within Dactylin (Fbxw4). However, all efforts to find the underlying cause for the human SHFM3 have failed on the analysis of all the genes within the linkage region. Intriguingly a submicroscopic duplication within the critical locus on chromosome 10q24 was associated with the phenotype. Methods and results As a part of screening for genomic rearrangements in cases with unexplained syndromic limb defects, a cohort of patients was analysed by array comparative genomic hybridisation (CGH). A 10q24 microduplication was detected in two individuals with distal limb deficiencies associated with micrognathia, hearing problems and renal hypoplasia. In addition, in a family with two affected siblings, a somatic/gonadal mosaicism for the microduplication was detected in the apparently healthy mother. Using a high resolution oligoarray further delineation of the duplication size was performed. Conclusions The detected 10q24 genomic imbalance in our syndromic patients has a similar size to the duplication in the previously reported individuals with an isolated form of SHFM, thus extending the clinical spectrum of SHFM3. These findings clearly demonstrate the importance of array CGH in the detection of the aetiology of complex, clinically heterogeneous entities.

Telomere healing following DNA polymerase arrest‐induced breakages is likely the main mechanism generating chromosome 4p terminal deletions

Constitutional developmental disorders are frequently caused by terminal chromosomal deletions. The mechanisms and/or architectural features that might underlie those chromosome breakages remain largely unexplored. Because telomeres are the vital DNA protein complexes stabilizing linear chromosomes against chromosome degradation, fusion, and incomplete replication, those terminal‐deleted chromosomes acquired new telomeres either by telomere healing or by telomere capture. To unravel the mechanisms leading to chromosomal breakage and healing, we sequenced nine chromosome 4p terminal deletion boundaries. A computational analysis of the breakpoint flanking region, including 12 previously published pure terminal breakage sites, was performed in order to identify architectural features that might be involved in this process. All terminal 4p truncations were likely stabilized by telomerase‐mediated telomere healing. In the majority of breakpoints multiple genetic elements have a potential to induce secondary structures and an enrichment in replication stalling site motifs were identified. These findings suggest DNA replication stalling‐induced chromosome breakage during early development is the first mechanistic step leading toward terminal deletion syndromes. Hum Mutat 31:1–9, 2010.

Progressive pseudorheumatoid arthritis of childhood (PPAC) and normal adult height.

Legius E, Mulier M, Van Damme B, Fryns JP. Progressive pseudorheumatoid arthritis of childhood (PPAC) and normal adult height.

Holoprosencephaly and ZIC2 microdeletions: novel clinical and epidemiological specificities delineated

Chabchoub E, Willekens D, Vermeesch JR, Fryns J‐P. Holoprosencephaly and ZIC2 microdeletions: novel clinical and epidemiological specificities delineated.

Piecing together the problems in diagnosing low- level chromosomal mosaicism

Low-level somatic chromosomal mosaicism, which usually arises from post-zygotic errors, is a known cause of several well defined genetic syndromes and has been implicated in various multifactorial diseases. It is, however, not easy to diagnose, as various physical and technical factors complicate its identification.

Cryptic trisomy 5q35.2qter and deletion 1p36.3 characterised using FISH and array-based CGH.

A 10(6/12)-year-old boy was referred to the genetics department because of mental retardation and dysmorphic findings including microcephaly, flat face, down-slanting palpebral fissures, strabismus, prominent ears, bulbous nasal tip, down-turned corners of the mouth, narrow palate, clinodactyly of the fifth fingers and generalised eczema. Cytogenetic analysis revealed a karyotype of 47,XY,+mar of paternal origin. Multicolour FISH showed the marker chromosome to be derived from chromosome 15. For further elucidation of the phenotype, array-based comparative genomic hybridisation (aCGH) was performed, which revealed dup(5)(q35.2qter) and del(1)(p36.3). Parental FISH analysis revealed that the translocation occurred de novo. Despite the presence of a clinical phenotype along with a microscopically visible chromosomal aberration, a complex cryptic cytogenetic abnormality was causative for the phenotype of the patient. Elucidation of this complex aberration required combination of the whole cytogenetic toolbox.

Prenatal Diagnosis of the Wolf-Hirschhorn Syndrome with Increased Nuchal Translucency and Negative Serum Integrated Screening for Trisomy 21

The Wolf-Hirschhorn syndrome (WHS) is a contiguous gene deletion syndrome associated with a hemizygous deletion of chromosome 4p16.3. It is characterized by pre- and postnatal growth restriction, microcephaly, profound learning disability and seizure disorder, a ‘Greek helmet’ facies, and closure defects (cleft lip or palate, coloboma of the eye and cardiac septal defects). Prenatal diagnosis of the WHS (deletion 4p syndrome) has been established after karyotyping mainly for intrauterine growth restriction often with hypospadias, facial clefting and diaphragmatic hernia. Here we report the prenatal diagnosis of WHS at 19 weeks with increased nuchal translucency at 12 weeks, but a favourable integrated screening test due to low levels of B-human chorionic gonadotrophin (hCG). Low levels of hCG have been previously reported in Wolf-Hirschhorn syndrome.

Pericardial effusion in the first trimester of pregnancy

Ingrid Witters1,2,6*, Derize Boshoff3, Luc De Catte4, Tinne Mesens2, Wilfried Gyselaers2, Claire Theyskens2, Els Bruneel2, Marc Gewillig5 and Jean-Pierre Fryns1 1Center for Human Genetics, Catholic University of Leuven, Leuven, Belgium 2Department of Obstetrics and Gynecology, St-Jans Hospital, Genk, Belgium 3Department of Pediatric Cardiology, St-Jans Hospital, Genk, Belgium 4Department of Obstetrics and Gynecology, Catholic University of Leuven, Leuven, Belgium 5Department of Pediatrics, Catholic University of Leuven, Leuven, Belgium 6GROW School of Oncology and Developmental Biology, Maastricht University Medical Centre, Leuven, Belgium