A novel biallelic LMNB2 variant in a patient with progressive myoclonus epilepsy and ataxia: A case of laminopathy.

The report of LMNB2-related progressive myoclonus epilepsy and ataxia due to missense homozygous c.473G>T variant.

Characterization of a Rare Mosaicism in Autosomal Translocation of t(5;21) Using Conventional Cytogenetics and FISH Methods

Background: Mosaicism of a normal cell population and an unbalanced autosomal chromosome rearrangement is rarely seen. If the abnormal cell line contributes to a minor part of soma, the phenotype is expected to be normal. Case Report: We report a 29-year-old woman who had balance chromosomal translocation of 46,XX,t(5;21) with a two-year-old affected girl, characterized by mental retardation, dystrophia, hearing impartment, and dysphagia. Methods and Results: Cytogenetic investigation revealed a low mosaic unbalanced translocation of 46,XX,t(5;21)/ 46,XX, which was confirmed by fluorescence in situ hybridization analysis. Studying 200 metaphases and interphases of peripheral blood sample revealed 70% partial monosomy of 21q22 and partial trisomy of 5q(35.3) and 30% of normal pattern. Conclusion: In rare cases such as this study, parents with balanced translocation with no phenotypes may lead to a mosaic unbalanced translocation with abnormal phenotypes in offspring, which underscores the need for prenatal karyotyping and genetics counseling.

Prenatal Diagnosis of Mosaic Tetrasomy 18p in a Case without Sonographic Abnormalities.

Small supernumerary marker chromosomes (sSMC) are still a major problem in clinical cytogenetics as they cannot be identified or characterized unambiguously by conventional cytogenetics alone. On the other hand, and perhaps more importantly in prenatal settings, there is a challenging situation for counseling how to predict the risk for an abnormal phenotype, especially in cases with a de novo sSMC. Here we report on the prenatal diagnosis of a mosaic tetrasomy 18p due to presence of an sSMC in a fetus without abnormal sonographic signs. For a 26-year-old, gravida 2 (para 1) amniocentesis was done due to consanguineous marriage and concern for Down syndrome, based on borderline risk assessment. Parental karyotypes were normal, indicating a de novo chromosome aberration of the fetus. FISH analysis as well as molecular karyotyping identified the sSMC as an i(18)(pter->q10:q10->pter), compatible with tetrasomy for the mentioned region. Cordocentesis was done due to normal sonography and the results from amniocentesis were confirmed. The parents opted for pregnancy termination and post mortem examination now noted, low anterior hairline, large philtrum, low-set posteriorly rotated malformed ears with prominent antihelix, lower limbs joint contracture and digital anomalies, including long and narrow toes with clinodactyly of the 1st and 5th toes and postaxial polydactyly of one hand. De novo i(18p) can be considered as a special case in the sense that the major relevant phenotypes mentioned for it, i.e. feeding difficulties, abnormalities in muscle tone and developmental/mental retardation, cognitive and behavioral characteristics, recurrent otitis media and seizures, are mostly postnatal. This emphasizes the necessity to determine the nature of a de novo euchromatic marker chromosome, especially in cases with normal ultrasound result and the suitability of a cordocentesis in order to better predicting the pregnancy outcome and parental counseling.