Complex rearranged small supernumerary marker chromosomes (sSMC), three new cases; evidence for an underestimated entity?

<p>Abstract</p> <p>Background</p> <p>Small supernumerary marker chromosomes (sSMC) are present ~2.6 × 10⁶human worldwide. sSMC are a heterogeneous group of derivative chromosomes concerning their clinical consequences as well as their chromosomal origin and shape. Besides the sSMC present in Emanuel syndrome, i.e. der(22)t(11;22)(q23;q11), only few so-called complex sSMC are reported.</p> <p>Results</p> <p>Here we report three new cases of unique complex sSMC. One was a <it>de novo </it>case with a dic(13 or 21;22) and two were maternally derived: a der(18)t(8;18) and a der(13 or 21)t(13 or 21;18). Thus, in summary, now 22 cases of unique complex sSMC are available in the literature. However, this special kind of sSMC might be under-diagnosed among sSMC-carriers.</p> <p>Conclusion</p> <p>More comprehensive characterization of sSMC and approaches like reverse fluorescence in situ hybridization (FISH) or array based comparative genomic hybridization (array-CGH) might identify them to be more frequent than only ~0.9% among all sSMC.</p

Interspecific hybridization in perennial species of Lathyrus (fabaceae)

In an attempt to introduce new variation into Lathyrus latifolius, the perennial pea, a programme of interspecific hybridization with several perennial and one annual Lathyrus species was undertaken. New interspecific hybrid combinations were produced involving three of the perennial species (L. latifolius, L. sylvestris, L. heterophyllus). Crosses with the annual species, L. gorgoni, were unsuccessful. These new hybrids are important additions to the limited number of Lathyrus hybrids. Meiotic analysis of the new hybrids and in particular the analysis of their pachytene pairing from spread synaptonemal complexes show that the low fertility of these hybrids is not due to structural differences between the chromosomes of the parental species. Some of the new hybrids that were produced showed unusual karyotypes and variation in meiotic chromosome pairing. (© Inra/Elsevier, Paris.)Hybridations interspécifiques entre espèces pérennes du genre Lathyrus (Fabaceae). Dans le but d'introduire une nouvelle variabilité chez Lathyrus latifolius, le pois pérenne, un programme d'hybridation interspécifique a été entrepris entre espèces de Lathyrus, plusieurs pérennes et une annuelle. De nouvelles combinaisons hybrides interspécifiques ont été obtenues, impliquant trois des espèces pérennes (L. latifolius, L. sylvestris et L. heterophyllus). Les croisements avec l'espèce annuelle, L. gorgoni furent infructueux. Ces nouveaux hybrides constituent un apport important au nombre limité d'hybrides de Lathyrus actuellement disponibles. L'analyse des méioses des nouveaux hybrides et en particulier l'analyse de l'appariement au pachytène à partir d'étalements de complexes synaptonémaux montre que la faible fertilité de ces hybrides n'est pas due à des différences structurelles entre les chromosomes des espèces parentales. Quelques uns de ces nouveaux hybrides ont présenté des caryotypes atypiques et une variation dans l'appariement des chromosomes à la méiose. (© Inra/Elsevier, Paris.

Molecular support for heterogonesis resulting in sesquizygotic twinning

Sesquizygotic multiple pregnancy is an exceptional intermediate between monozygotic and dizygotic twinning. We report a monochorionic twin pregnancy with fetal sex discordance. Genotyping of amniotic fluid from each sac showed that the twins were maternally identical but chimerically shared 78% of their paternal genome, which makes them genetically in between monozygotic and dizygotic; they are sesquizygotic. We observed no evidence of sesquizygosis in 968 dizygotic twin pairs whom we screened by means of pangenome single-nucleotide polymorphism genotyping. Data from published repositories also show that sesquizygosis is a rare event. Detailed genotyping implicates chimerism arising at the juncture of zygotic division, termed heterogonesis, as the likely initial step in the causation of sesquizygosis.</p

Cat eye syndrome: Clinical, cytogenetics and familial findings in a large cohort of 43 patients highlighting the importance of congenital heart disease and inherited cases

Cat Eye Syndrome (CES) is a rare genetic disease caused by the presence of a small supernumerary marker chromosome derived from chromosome 22, which results in a partial tetrasomy of 22p‐22q11.21. CES is classically defined by association of iris coloboma, anal atresia, and preauricular tags or pits, with high clinical and genetic heterogeneity. We conducted an international retrospective study of patients carrying genomic gain in the 22q11.21 chromosomal region upstream from LCR22‐A identified using FISH, MLPA, and/or array‐CGH. We report a cohort of 43 CES cases. We highlight that the clinical triad represents no more than 50% of cases. However, only 16% of CES patients presented with the three signs of the triad and 9% not present any of these three signs. We also highlight the importance of other impairments: cardiac anomalies are one of the major signs of CES (51% of cases), and high frequency of intellectual disability (47%). Ocular motility defects (45%), abdominal malformations (44%), ophthalmologic malformations (35%), and genitourinary tract defects (32%) are other frequent clinical features. We observed that sSMC is the most frequent chromosomal anomaly (91%) and we highlight the high prevalence of mosaic cases (40%) and the unexpectedly high prevalence of parental transmission of sSMC (23%). Most often, the transmitting parent has mild or absent features and carries the mosaic marker at a very low rate (<10%). These data allow us to better delineate the clinical phenotype associated with CES, which must be taken into account in the cytogenetic testing for this syndrome. These findings draw attention to the need for genetic counseling and the risk of recurrence