Tetrasomy 18p syndrome is a rare chromosomal disorder that is caused by the presence of isochromosome 18p. Most tetrasomy 18p cases are de novo cases and maternal origin of trisomy 18p is a rare condition. At present, only four cases of maternal origin have been reported in worldwide.This is the fifth case of tetrasomy 18p originating from maternal trisomy 18p. The mother of the fetus studied had no apparent disease phenotype. The current case report is to describe a fetus with confirmed 18p tetrasomy as detected by karyotyping and Single Nucleotide Polymorphism array (SNP array) analysis. However, the fetus showed normal phenotypic features that were observed using ultrasound scans. The mother and maternal grandfather were phenotypically normal and healthy; however, they were diagnosed with trisomy 18p, which was confirmed by conventional karyotyping and SNP array. We report a case of 18p tetrasomy in a fetus whose mother and grandfather had 18p trisomy. The mother and grandfather were phenotypically normal. Our case report findings provide an important reference for the genetic counseling of trisomy 18p in the future.

Small supernumerary marker chromosomes (sSMC) are a heterogeneous group of structurally abnormal chromosomes, with an incidence of 0,044% in newborns that increases up to almost 7 times in developmentally retarded patients. sSMC from all 24 chromosome have been described, most of them originate from the group of the acrocentric, with around half deriving from the chromosome 15. Non-acrocentric sSMC are less common and, in the 30 percent of the cases, are associated with phenotypic effect. Complex sSMC consist of chromosomal material derived from more than one chromosome. Genotype-phenotype correlations in patients with sSMC are difficult to assess. Clinical features depend on factors such as its size, genetic content, the involvement of imprinted genes which may be influenced by uniparental disomy and the level of mosaicism. Trisomy of the short arm of chromosome 18 (18p) is an infrequent finding and does not appear to be associated with a specific syndrome. However, mild intellectual disability with or without other anomalies is reported in almost one-third of the patients. Here we present clinical and molecular characterization of a new case of de novo complex sSMC consisting of the entire short arm of chromosome 18p associated with a centromere of either chromosome 13 or 21, evidenced in a 5-year-old boy during diagnostic workup for moderate intellectual disability and dysmorphisms. To date, only seven cases of isolated trisomy 18p due to a sSMC have been reported, three of which have been characterized by array CGH. In two of them the breakpoints and the size of the duplication have been described. In the manuscript we also reviewed cases reported in the DECIPHER database carrying similar duplication and also considered smaller duplications within the region of interest, in order to evaluate the presence of critical regions implicated in the pathological phenotype. Our case provides additional information about phenotypic effects of pure trisomy 18p, confirms chromosomal microarray analysis as gold standard to characterize complex sSMC, and supplies additional elements for genetic counselling.

To delineate the nature and origin of chromosomal aberration in a girl with mental retardation. Genomic DNA was analyzed by using single nucleotide polymorphism-based array (SNP array). The proband and her parents were subjected to routine G-banded chromosomal karyotyping analysis. SNP array has identified a 1.2 Mb microdeletion at 10p15.3 and a duplication at 18p11.21-pter in the proband. The patient was also found to harbor a structural aberration involving 10p. The karyotype of her father was 46,XY,t(10;18)(p15;p11.2), while her mother was found to be normal. The structural aberration of 10p carried by the patient has derived from her father whom has carried a balanced translocation of t(10;18). Her karyotype was finally determined as 46,XX,der(10)t(10;18)(p15;p11.2)pat. The abnormal phenotype of the patient can probably be attributed to the presence of 10p15.3 microdeletion and 18p11.21-pter duplication.

Background: Chromosomal deletion involving the 6p25 region results in a clinically recognizable syndrome characterized by anterior eye chamber anomalies with risk of glaucoma and non-ocular malformations (6p25 deletion syndrome). We report a newborn infant case of childhood glaucoma with a combination of partial monosomy 6p25 and partial trisomy 18p11 due to an unbalanced translocation.Materials and methods: The patient was a 0-year-old girl. Both eyes showed aniridia and left eye Peters anomaly with multiple malformations. To identify the chromosomal aberrations in the patient with clinically suspected 6p25 deletion syndrome, we performed cytogenetic analysis (G-banding and multicolor fluorescent in-situ hybridization) and array-based comparative genomic hybridization (array-CGH) analysis.Results: Cytogenetic analyses revealed a derivative chromosome 6 with its distal short arm replaced by an extra copy of the short arm of chromosome 18. Array-CGH analysis detected a 4.6-Mb deletion at 6pter to 6p25.1 and 8.9-Mb duplication at 18pter to 18p11.22. To determine the breakpoint of the unbalanced rearrangement at the single-base level, we performed a long-range PCR for amplifying the junctional fragment of the translocation breakpoint. By sequencing the junctional fragment, we defined the unbalanced translocation as g.chr6:pter_4594783delinschr18:pter_8911541.Conclusions: A phenotype corresponding to combined monosomy 6p25 and trisomy 18p11 presented as childhood glaucoma associated with non-acquired (congenital) ocular anomalies consist of aniridia and Peters anomaly and other systemic malformations. To the best of our knowledge, this is the first report which demonstrated the breakpoint sequence of an unbalanced translocation in a Japanese infant with childhood glaucoma.

An external quality assessment for detection of trisomy 21, 18, and 13 by massively parallel sequencing was implemented by the National Center for Clinical Laboratories of People's Republic of China in 2014. Simulated samples were prepared by mixing fragmented abnormal DNA with plasma from non-pregnant women. The external quality assessment panel, comprising 5 samples from pregnant healthy women, 2 samples with sex chromosome aneuploidies, and 13 samples with different concentrations of fetal fractions positive for trisomy 21, 18, and 13, was then distributed to participating laboratories. In total, 55.6% (47 of 84) of respondents correctly identified each of the samples in the panel. Seventeen false-negative and 87 gray zone results were reported, most [102 of 104 (98.1%)] of which were derived from for trisomy samples with effective fetal fractions <4%. No laboratories generated false-positive results. In addition, we observed varied diagnostic capabilities of different assays, with the assay on the basis of NextSeq CN500 performing better than others, whereas Z values generated by BGISEQ-100 fluctuated greatly. There were no significant correlations between the numbers of unique sequence reads and Z values from any trisomy sample generated by BGISEQ-100. Overall, most clinical laboratories detected samples containing effective fetal fractions >4%. Our study shows need for further laboratory training in the management of samples with low fetal fractions. For some assays, precision of Z values needs to be improved.