Cytogenetics and Molecular Investigations detect a Mosaic Variant of Turner Syndrome only Suspected by Non-Invasive Prenatal Testing: Two Case Reports with Negative Ultrasound Examinations.

Prenatal testing has been moving towards non-invasive methods to determine fetal risk for genetic disorders. Numerous studies have focused the attention on common trisomies; although the detection rate (DR) for trisomy 21 is high (over 95%), the accuracy regarding the DR for trisomies 13 and 18 has come under scrutiny. The testing has been applied to sex chromosome aneuploidies, but many studies have shown that it is not as effective as it is for common trisomies. Although non-invasive prenatal test (NIPT) has become a standard screening procedure for all pregnant women, invasive sampling procedures remain important in confirming NIPT-positive findings. In the present study, we report discordant results of Turner syndrome (TS) mosaicism between NIPT and karyotyping. A 35-year-old pregnant woman underwent NIPT, and a probable risk for Xp deletion was indicated. Subsequently, amniocentesis was performed. The karyotype was identified as mos 45,X [28]/46,X,i(X)(q1.0)[5]. In the second case, a 33-year-old woman underwent amniocentesis after a positive NIPT that indicated a probable risk for monosomy X. The result was mos 45,X [8]/46,XY[8]. Since NIPT is a screening test, the possibility of false-positive or false-negative results should always be considered. We underline the importance of pre/post detailed counseling. Furthermore, women with abnormal NIPT results should undergo immediate amniocentesis that remains the only tool for a correct diagnosis of sex chromosome aneuploidies.

A familial chromosomal complex rearrangement confirms RUNX1T1 as a causative gene for intellectual disability and suggests that 1p22.1p21.3 duplication is likely benign.

BACKGROUND: Complex chromosomal rearrangements are constitutive structural aberrations involving three or more breaks. They can be balanced or unbalanced and result in different outcomes, depending on deletion/duplication of genomic material, gene disruption, or position effects. CASE PRESENTATION: We report on a patient presenting with severe anemia, splenomegaly, mild intellectual disability and facial dysmorphisms harboring a 4.3 Mb duplication at 1p22.1p21.3 and a 2.1 Mb deletion at 8q21.3q22.1, involving RUNX1T1 gene. The healthy brother presented the same duplication of chromosome 1p as at 1p22.1p21.3. CONCLUSIONS: The rearrangement found both these siblings resulted from malsegregation in the proband and recombination in her healthy brother of a balanced paternal complex chromosomal rearrangement. These results confirm RUNX1T1 as a causative gene for intellectual disability and suggest the 1p22.1p21.3 duplication is likely benign.

First Report of Low-Rate Mosaicism for 20q11.21q12 Deletion and Delineation of the Associated Disorder.

Interstitial deletions of the long arm of chromosome 20 are very rare, with only 12 reported patients harboring the 20q11.2 microdeletion and presenting a disorder characterized by psychomotor and growth delay, dysmorphisms, and brachy-/clinodactyly. We describe the first case of mosaic 20q11.2 deletion in a 5-year-old girl affected by mild psychomotor delay, feeding difficulties, growth retardation, craniofacial dysmorphisms, and finger anomalies. SNP array analysis disclosed 20% of cells with a 20q11.21q12 deletion, encompassing the 20q11.2 minimal critical region and the 3 OMIM disease-causing genes GDF5, EPB41L1, and SAMHD1. We propose a pathogenic role of other genes mapping outside the small region of overlap, in particular GHRH (growth hormone releasing hormone), whose haploinsufficiency could be responsible for the prenatal onset of growth retardation which is shared by half of these patients. Our patient highlights the utility of chromosomal microarray analysis to identify low-level mosaicism.

Defective kinesin binding of TUBB2A causes progressive spastic ataxia syndrome resembling sacsinopathy.

Microtubules participate in fundamental cellular processes, including chromosomal segregation and cell division, migration and intracellular trafficking. Their proper function is required for correct central nervous system development and operative preservation, and mutations in genes coding tubulins, the constituting units of microtubules, underlie a family of neurodevelopmental and neurodegenerative diseases, collectively known as 'tubulinopathies', characterized by a wide range of neuronal defects resulting from defective proliferation, migration and function. Here, we causally link a previously unreported missense mutation in TUBB2A (c.1249G>A, p.D417N), encoding one of the neuron-specific ß-tubulin isotype II, to a disorder characterized by progressive spastic paraplegia, peripheral sensory-motor polyneuropathy and ataxia. Asp417 is a highly conserved solvent-exposed residue at the site mediating binding of kinesin superfamily motors. Impaired binding to KIF1A, a neuron-specific kinesin required for transport of synaptic vesicle precursors of the disease-associated TUBB2A mutant, was predicted by structural analyses and confirmed experimentally in vitro. We show that overexpression of TUBB2AD417N disrupts the mitotic spindle bipolarity and morphology and affects the M phase entry and length. Differently from the TUBB2AN247K and TUBB2AA248V, two mutants previously identified to affect neurodevelopment, TUBB2AD417N retains the ability to assemble into microtubules. Consistent with the differential clinical and structural impact, TUBB2AA248V does not drastically affect TUBB2A binding to KIF1A, nor mitotic spindle bipolarity. Overall, our data demonstrate a pathogenic role of the p.D417N substitution that is different from previously reported TUBB2A mutations and expand the phenotypic spectrum associated with mutations in this gene.

Aged induced pluripotent stem cell (iPSCs) as a new cellular model for studying premature aging.

Nuclear integrity and mechanical stability of the nuclear envelope (NE) are conferred by the nuclear lamina, a meshwork of intermediate filaments composed of A- and B-type lamins, supporting the inner nuclear membrane and playing a pivotal role in chromatin organization and epigenetic regulation. During cell senescence, nuclear alterations also involving NE architecture are widely described. In the present study, we utilized induced pluripotent stem cells (iPSCs) upon prolonged in vitro culture as a model to study aging and investigated the organization and expression pattern of NE major constituents. Confocal and four-dimensional imaging combined with molecular analyses, showed that aged iPSCs are characterized by nuclear dysmorphisms, nucleoskeletal components (lamin A/C-prelamin isoforms, lamin B1, emerin, and nesprin-2) imbalance, leading to impaired nucleo-cytoplasmic MKL1 shuttling, actin polymerization defects, mitochondrial dysfunctions, SIRT7 downregulation and NF-kBp65 hyperactivation. The observed age-related NE features of iPSCs closely resemble those reported for premature aging syndromes (e.g., Hutchinson-Gilford progeria syndrome) and for somatic cell senescence. These findings validate the use of aged iPSCs as a suitable cellular model to study senescence and for investigating therapeutic strategies aimed to treat premature aging.

Unclassifiable pattern of hypopigmentation in a patient with mosaic partial 12p tetrasomy without Pallister-Killian syndrome.

Pallister-Killian syndrome (PKS-#OMIM601803) is a multisystem developmental disorder typically due to the presence of an aneuploidy cell line, consisting of a supernumerary tetrasomic chromosomal marker (SCM) arisen from the short arm of chromosome 12 (12p isochromosome). The clinical phenotype, which is strictly related to the percentage and tissue distribution of aneuploid cells, is characterized by craniofacial dysmorphisms, pigmentary skin anomalies, limb shortening, congenital heart defects, diaphragmatic hernia, hypotonia, intellectual disability, and epilepsy. We report on a 4 year-old girl harboring a 12p partial isochromosome, involving the PKS critical region, affecting about 70% of circulating lymphocytes, urine, and saliva cells and fibroblast from a hyperpigmented skin spot, and 100% of fibroblasts from a hypopigmented skin spot. Interestingly, despite the high proportion of affected cells this patient did not present with PKS, and a pattern of linear and patchy pigmentary mosaicism was the sole clinical manifestation. The present observation suggests that partial 12p SCM can also result in mild phenotypes, and its prevalence in the human population could have been underestimated. Accurate dermatologic evaluation could be a major handle for genetic testing.

Interstitial 10q21.1q23.31 Duplication due to Meiotic Recombination of a Paternal Balanced Complex Rearrangement: Cytogenetic and Molecular Characterization.

Complex chromosomal rearrangements (CCRs) are structural aberrations involving more than 2 chromosomal breakpoints. They are associated with different outcomes depending on the deletion/duplication of genomic material, gene disruption, or position effects. Balanced CCRs can also undergo missegregation during meiotic division, leading to unbalanced derivative chromosomes and, in some cases, to affected offspring. We report on a patient presenting with developmental and speech delay, growth retardation, microcephaly, hypospadias, and dysmorphic features, harboring an interstitial 10q21.1q23.31 duplication, due to recombination of a paternal CCR. Application of several cytogenetic and molecular techniques allowed determining the biological bases of the rearrangement, understanding the underlying chromosomal mechanism, and assessing the reproductive risk.