BackgroundSmall Supernumerary Marker Chromosomes (sSMC) are rare chromosomal abnormalities, which have abnormal banding arrangement and take many shapes. Several disorders have been correlated with sSMC presence. The aim of this study is to characterize the sSMC derived from chromosome 18 by Fluorescence in situ hybridization (FISH) and Array Comparative Genomic Hybridization (aCGH).ResultsNine children with dysmorphic features have been investigated. They have these features in common: a triangular face, low-set ears, a large mouth with a thin upper lip, and a horizontal palpebral fissure. Epicanthus and strabismus were present in two patients. In addition, we have noticed microcephaly and mental and/or developmental delay with low birth weight. However, two patients had standard birth weight; one patient had hypospadias; two had skin problems; and three showed different congenital heart defects. One patient had corpus callosum hypoplasia. Systematic karyotype analysis revealed a de novo supernumerary chromosome. Array CGH showed a gain in copy number on the short arm of chromosome 18 in the nine cases. In one case, the sSMC seemed to be in mosaic. The breakpoints of the marker were identified using aCGH and FISH. Thus, the sSMC led to 18p tetrasomy with approximately 14 Mb lengths, between 364344 and 14763575 based on the human genome version 18.ConclusionsThese results have been completed by FISH in order to ascertain the shape of the sSMC. Our results confirm the uniqueness and particularity of the iso18p syndrome on the phenotypic as well as on the genetic level.
Background
Wolf–Hirschhorn (WHS) is a set of congenital physical anomalies and mental retardation associated with a partial deletion of the short arm of chromosome 4. To establish a genotype–phenotype correlation; we carried out a molecular cytogenetic analysis on two Tunisian WHS patients. Patient 1 was a boy of 1-year-old, presented a typical WHS phenotype while patient 2, is a boy of 2 days presented an hypospadias, a micropenis and a cryptorchidie in addition to the typical WHS phenotype. Both the array comparative genomic hybridization and fluorescence in situ hybridization techniques were used.
Results
Results of the analysis showed that patient 2 had a greater deletion size (4.8 Mb) of chromosome 4 than patient 1 (3.4 Mb). Here, we notice that the larger the deletion, the more genes are likely to be involved, and the more severe the phenotype is likely to be. If we analyze the uncommon deleted region between patient1 and patient 2 we found that the Muscle Segment Homeobox (MSX1) gene is included in this region. MSX1 is a critical transcriptional repressor factor, expressed in the ventral side of the developing anterior pituitary and implicated in gonadotrope differentiation. Msx1 acts as a negative regulatory pituitary development by repressing the gonadotropin releasing hormone (GnRH) genes during embryogenesis. We hypothesized that the deletion of MSX1 in our patient may deregulate the androgen synthesis.
Conclusion
Based on the MSX1 gene function, its absence might be indirectly responsible for the hypospadias phenotype by contributing to the spatiotemporal regulation of GnRH transcription during development.
Williams Beuren Syndrome (WBS): Well-studied multisystemic disorder caused by a 1.5Mb hemizygous deletion of about 28 genes on 7q11.23. Characteristic pattern of symptoms: typical facial dysmorphisms, congenital cardiopathy, weakness of connective tissue, intellectual disability and a characteristic cognitive profile that includes relative strengths in verbal term memory and lexical comprehension.
Clinical and molecular findings in nine new cases of tetrasomy 18p syndrome: Co-occurrence of isochromosome 18p and Copy Number Variation Background: Tetrasomy 18p (T18p) (OMIM: # 614290) is a rare chromosomal abnormality that results from the presence of a supernumerary chromosome known as isochromosome 18p. It is one of the most frequent isochromosomes observed in humans with a prevalence of 1/180000 live born children. This syndrome is associated with a distinctive facial appearance, feeding difficulties in infancy, development delay and intellectual disability. In this study, we report on the clinical and molecular cytogenetic findings of nine Tunisian cases of isochromosome 18p (I18p) in patients having in common dysmorphic features and development delay and/or intellectual disability with slightly variable phenotypes.
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