Elena Mansilla

Molecular characterisation of a mosaicism with a complex chromosome rearrangement: evidence for coincident chromosome healing by telomere capture and neo-telomere formation

Background: Broken chromosomes must acquire new telomeric “caps” to be structurally stable. Chromosome healing can be mediated either by telomerase through neo-telomere synthesis or by telomere capture. Aim: To unravel the mechanism(s) generating complex chromosomal mosaicisms and healing broken chromosomes. Methods: G banding, array comparative genomic hybridization (aCGH), fluorescence in-situ hybridisation (FISH) and short tandem repeat analysis (STR) was performed on a girl presenting with mental retardation, facial dysmorphism, urogenital malformations and limb anomalies carrying a complex chromosomal mosaicism. Results & discussion: The karyotype showed a de novo chromosome rearrangement with two cell lines: one cell line with a deletion 9pter and one cell line carrying an inverted duplication 9p and a non-reciprocal translocation 5pter fragment. aCGH, FISH and STR analysis enabled the deduction of the most likely sequence of events generating this complex mosaic. During embryogenesis, a double-strand break occurred on the paternal chromosome 9. Following mitotic separation of both broken sister chromatids, one acquired a telomere vianeo-telomere formation, while the other generated a dicentric chromosome which underwent breakage during anaphase, giving rise to the del inv dup(9) that was subsequently healed by chromosome 5 telomere capture. Conclusion: Broken chromosomes can coincidently be rescued by both telomere capture and neo-telomere synthesis.

New microdeletion and microduplication syndromes: a comprehensive review

Several new microdeletion and microduplication syndromes are emerging as disorders that have been proven to cause multisystem pathologies frequently associated with intellectual disability (ID), multiple congenital anomalies (MCA), autistic spectrum disorders (ASD) and other phenotypic findings. In this paper, we review the “new” and emergent microdeletion and microduplication syndromes that have been described and recognized in recent years with the aim of summarizing their main characteristics and chromosomal regions involved. We decided to group them by genomic region and within these groupings have classified them into those that include ID, MCA, ASD or other findings. This review does not intend to be exhaustive but is rather a quick guide to help pediatricians, clinical geneticists, cytogeneticists and/or molecular geneticists.

Customized high resolution CGH‐array for clinical diagnosis reveals additional genomic imbalances in previous well‐defined pathological samples

High‐resolution array comparative genomic hybridization (aCGH) is a powerful molecular cytogenetic tool that is being adopted for diagnostic evaluation of genomic imbalances and study disease mechanisms and pathogenesis. We report on the design and use, of a custom whole‐genome oligonucleotide‐based array (called KaryoArray®v3.0; Agilent‐based 8 × 60 K) for diagnostic setting, which was able to detect new and unexpected rearrangements in 11/63 (∼17.5%) of previous known pathological cases associated with known genetic disorders, and in the second step it identified at least one causal genomic imbalance responsible of the phenotype in ∼20% of patients with psychomotor development delay and/or intellectual disability. To validate the array, first; we blindly tested 120 samples; 63 genomic imbalances that had previously been detected by karyotyping, FISH and/or MLPA, and 57 sex‐matched control samples from healthy individuals; secondly a prospective study of 540 patients with intellectual disabilities, autism spectrum disorder and multiple congenital anomalies were evaluated to confirm the utility of the tool. These data indicate that implementation of array technologies as the first‐tier test may reveal that additional genomic imbalances could co‐exist in patients with trisomies and classical del/dup syndromes, suggesting that aCGH may also be indicated in these individuals, at least when phenotype does not match completely with genotype.

Characterization of a 8q21.11 Microdeletion Syndrome Associated with Intellectual Disability and a Recognizable Phenotype

We report eight unrelated individuals with intellectual disability and overlapping submicroscopic deletions of 8q21.11 (0.66-13.55 Mb in size). The deletion was familial in one and simplex in seven individuals. The phenotype was remarkably similar and consisted of a round face with full cheeks, a high forehead, ptosis, cornea opacities, an underdeveloped alae, a short philtrum, a cupids bow of the upper lip, down-turned corners of the mouth, micrognathia, low-set and prominent ears, and mild finger and toe anomalies (camptodactyly, syndactyly, and broadening of the first rays). Intellectual disability, hypotonia, decreased balance, sensorineural hearing loss, and unusual behavior were frequently observed. A high-resolution oligonucleotide array showed different proximal and distal breakpoints in all of the individuals. Sequencing studies in three of the individuals revealed that proximal and distal breakpoints were located in unique sequences with no apparent homology. The smallest region of overlap was a 539.7 kb interval encompassing three genes: a Zinc Finger Homeobox 4 (ZFHX4), one microRNA of unknown function, and one nonfunctional pseudogen. ZFHX4 encodes a transcription factor expressed in the adult human brain, skeletal muscle, and liver. It has been suggested as a candidate gene for congenital bilateral isolated ptosis. Our results suggest that the 8q21.11 submicroscopic deletion represents a clinically recognizable entity and that a haploinsufficient gene or genes within the minimal deletion region could underlie this syndrome.

A New Overgrowth Syndrome is Due to Mutations in RNF125.

Overgrowth syndromes (OGS) are a group of disorders in which all parameters of growth and physical development are above the mean for age and sex. We evaluated a series of 270 families from the Spanish Overgrowth Syndrome Registry with no known OGS. We identified one de novo deletion and three missense mutations in RNF125 in six patients from four families with overgrowth, macrocephaly, intellectual disability, mild hydrocephaly, hypoglycemia, and inflammatory diseases resembling Sjögren syndrome. RNF125 encodes an E3 ubiquitin ligase and is a novel gene of OGS. Our studies of the RNF125 pathway point to upregulation of RIG‐I‐IPS1‐MDA5 and/or disruption of the PI3K‐AKT and interferon signaling pathways as the putative final effectors.

Analysis of invdupdel(8p) rearrangement: Clinical, cytogenetic and molecular characterization

Inverted duplication 8p associated with deletion of the short arms of chromosome 8 (invdupdel[8p]) is a relatively uncommon complex chromosomal rearrangement, with an estimated incidence of 1 in 10,000–30,000 live borns. The chromosomal rearrangement consists of a deletion of the telomeric region (8p23‐pter) and an inverted duplication of the 8p11.2–p22 region. Clinical manifestations of this disorder include severe to moderate intellectual disability and characteristic facial features. In most cases, there are also CNS associated malformations and congenital heart defects. In this work, we present the cytogenetic and molecular characterization of seven children with invdupdel(8p) rearrangements. Subsequently, we have carried out genotype–phenotype correlations in these seven patients. The majority of our patients carry a similar deletion but different size of duplications; the latter probably explaining the phenotypic variability among them. We recommend that complete clinical evaluation and detailed chromosomal microarray studies should be undertaken, enabling appropriate genetic counseling.

Screening for subtelomeric chromosome alteration in a consecutive series of newborns with congenital defects.

It is generally accepted that 2.5% of the patients with unexplained mental retardation and dysmorphic features have a chromosome alteration affecting the subtelomeric regions. The frequency of such alterations whether in the general population or in newborns with congenital defects, however, remains unknown. Here, we present an analysis of the subtelomeric regions in a consecutive series of 71 newborn babies with congenital defects, who displayed a normal high resolution G-band karyotype (550–850 bands). After excluding the alterations that could be considered to be polymorphisms, a total of seven subtelomeric anomalies were observed with a frequency of 9.86% (3.96–20.31). We conclude that fluorescence in-situ hybridization screening for subtelomeric alterations is relevant for infants with congenital defects detectable at birth, particularly in those newborn babies with congenital defects and a normal high resolution G-band karyotype.

Additional case of an uncommon 22q11.2 reciprocal rearrangement in a phenotypically normal mother of children with 22q11.2 deletion and 22q11.2 duplication syndromes.

Additional Case of an Uncommon 22q11.2 Reciprocal Rearrangement in a Phenotypically Normal Mother of Children With 22q11.2 Deletion and 22q11.2 Duplication Syndromes Luis Fern andez,* Juli an Nevado, Mar ıa L. De Torres, Elena Mansilla, Elena Vallesp ın, Sixto Garc ıa-Mi~na ur, Rebeca Palomo, Luc ıa Deir os, Marta Cabrera, Elia Dina Galo, Pablo Lapunzina, and Alicia Delicado Instituto de Gen etica M edica y Molecular (INGEMM), IdiPAZ, Hospital Universitario La Paz, Universidad Aut onoma de Madrid, Madrid, Spain CIBER de Enfermedades Raras (CIBERER), ISCIII, Madrid, Spain Servicio de Cardiolog ıa Infantil, Hospital Universitario La Paz, Madrid, Spain Servicio de Neonatolog ıa, Hospital Universitario La Paz, Madrid, Spain Universidad Nacional Aut onoma de Nicaragua, Le on, Nicaragua

Familial imbalance in 16p13.11 leads to a dosage compensation rearrangement in an unaffected carrier

BackgroundWe and others have previously reported that familial cytogenetic studies in apparently de novo genomic imbalances may reveal complex or uncommon inheritance mechanisms.MethodsA familial, combined genomic and cytogenetic approach was systematically applied to the parents of all patients with unbalanced genome copy number changes.ResultsDiscordant array-CGH and FISH results in the mother of a child with a prenatally detected 16p13.11 interstitial microduplication disclosed a balanced uncommon rearrangement in this chromosomal region. Further dosage and haplotype familial studies revealed that both the maternal grandfather and uncle had also the same 16p duplication as the proband. Genomic compensation observed in the mother probably occurred as a consequence of interchromosomal postzygotic nonallelic homologous recombination.ConclusionsWe emphasize that such a dualistic strategy is essential for the full characterization of genomic rearrangements as well as for appropriate genetic counseling.