Trisomy 18p caused by a supernumerary marker with a chromosome 13/21 centromere: a possible recurrent chromosome aberration

Molecular characterization of a complex small supernumerary marker chromosome derived from chromosome 18p: an addition to the literature

Background

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.

Case presentation

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.

Conclusions

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.

Molecular cytogenetic characterization of small supernumerary marker 15 in infertile male: A case report

Small supernumerary marker chromosomes (sSMCs) are defined as structurally abnormal chromosomes that may be detected pre- or postnataly in patients with developmental and/or mental retardation or infertility. sSMC on chromosome 15 accounts for the highest proportion of all sSMCs and may be detected in subfertile individuals. The present study reports the case of a male patient with oligoasthenoteratozoospermia and an sSMC. The sSMC was identified and characterized according to G-banding analysis, chromosomal microarray analysis (CMA) and fluorescence in situ hybridization (FISH) analysis. Chromosomal karyotype analysis suggested that the patient presented with 47,XY,+mar. CMA was used to characterize the sSMC, which revealed a 0.44-Mb microduplication in 6q25.3q26. Subsequently, FISH using centromere-specific probes for chromosomes 13/21, 14/22 and 15 was applied to identify the origin of the sSMC, which was finally determined to be inverted duplicated(15)(q11.2). It was hypothesized that heterochromatin in the sSMC is responsible for the patient's fertility problem. The presence of heterochromatin may disrupt regular meiosis, thereby affecting normal spermatogenesis. Impaired spermatogenesis in infertile males with an sSMC derived from chromosome 15 was also reviewed by searching published literature and the sSMC database (http://ssmc-tl.com/sSMC.html). For patients with low sperm parameters and complete absence of spermatozoa in the ejaculate, including infertile males with an sSMC with spermatozoa, intracytoplasmic sperm injection is considered as an effective assisted reproductive technique. It may be concluded that molecular cytogenetic techniques are critical tools for delineating sSMCs in infertile males and may be beneficial in identifying sSMC carriers to ensure they receive clinical genetic counseling.

Two-Generation Transmission of Trisomy 18p: Prenatal Diagnosis in a Woman with Mild Intellectual Disability

Trisomy 18p is a rarely observed chromosomal aberration. Only 31 cases have previously been described in the literature. Trisomy 18p is associated with mild to moderate phenotypic anomalies and intellectual disability. Here, we report on a pregnant woman in whom noninvasive prenatal testing indicated a high risk of fetal trisomy 18. Prenatal diagnosis and karyotyping of the parents were performed and demonstrated that both the mother and the fetus had a derivative chromosome 15 with a segment of unknown origin. Chromosomal microarray analysis and FISH revealed a 14.9-Mb duplication of 18p and detected 3 centromeres of chromosome 18. To our knowledge, this is the first study reporting trisomy 18p due to an unbalanced translocation of 18p onto chromosome 15q showing 2-generation transmission. The results suggest that trisomy 18p can be considered a euchromatic variant.

47,XY,+der(X)t(X;18)(p11.4;p11.22): A Unique Aneuploidy Associated with Klinefelter Syndrome due to an Extra Derivative X Chromosome Inherited Maternally

A derivative X chromosome formed by translocation involving an X chromosome and a chromosome 18 in a Klinefelter syndrome (KS) patient with a 47,XXY karyotype has not been reported before. In this study, we present the clinical and molecular cytogenetic characteristics. The patient presented with small testes and azoospermia. G-banding analysis identified the karyotype as 47,XY,del(X)(p?11.4). Array CGH detected a 10.36-Mb duplication of chromosome region 18p11.22p11.32 (14,316-10,377,516) and a 111.18-Mb duplication of chromosome region Xp11.4q28 (61,931, 689-155,111,583), in addition to the normal chromosome 18 and an X chromosome. FISH results further revealed the extra 18p located at the end of the short arm of a deleted X chromosome, forming a derivative X chromosome. Finally, we identified the karyotype of the patient as 47,XY,+der(X)t(X;18)(p11.4;p11.22). The derivative X chromosome was maternally inherited. To our knowledge, this rare karyotype has not yet been reported in the literature. The present study may suggest a novel karyotype associated with KS.

Azoospermia and trisomy 18p syndrome: a fortuitous association? A patient report and a review of the literature

Complete, isolated trisomy of the short arm of chromosome 18 is very rare. To date, only 24 cases of trisomy 18p have been reported in the literature, making it difficult to define a potentially associated phenotype. However, the available evidence suggests that few clinical features are shared by these patients: only variable intellectual disability, variable facial dysmorphism and epilepsy are reported in a few patients. Although three inherited cases of trisomy 18p have already been reported, all were of maternal origin.

We report on a patient carrying an isolated complete trisomy 18p translocated to the short arm of chromosome 14 and presenting with facial dysmorphism, mild intellectual disability and non-obstructive azoospermia.

Chromosomal abnormalities are more frequent in infertile men with poor sperm quality than the general population. Both numerical and structural chromosomal aberrations have been already reported within the context of azoospermia. To our knowledge, this is the first patient with trisomy 18p to present a fertility impairment due to totally altered spermatogenesis and azoospermia. Although fertility disorders were not mentioned in the four previous reports of men with trisomy 18p, none of the latter had children. We suggest that azoospermia is a previously uncharacterized feature of trisomy 18p syndrome. We further hypothesize that two mechanisms could be responsible of the fertility impairment: a meiotic synapsis defect due to the additional 18p arm that blocks meiosis, and/or overexpression of a gene located on the 18p chromosome involved in the normal testicular development.

Array-CGH analysis in Rwandan patients presenting development delay/intellectual disability with multiple congenital anomalies

Background

Array-CGH is considered as the first-tier investigation used to identify copy number variations. Right now, there is no available data about the genetic etiology of patients with development delay/intellectual disability and congenital malformation in East Africa.

Methods

Array comparative genomic hybridization was performed in 50 Rwandan patients with development delay/intellectual disability and multiple congenital abnormalities, using the Agilent’s 180 K microarray platform.

Results

Fourteen patients (28%) had a global development delay whereas 36 (72%) patients presented intellectual disability. All patients presented multiple congenital abnormalities. Clinically significant copy number variations were found in 13 patients (26%). Size of CNVs ranged from 0,9 Mb to 34 Mb. Six patients had CNVs associated with known syndromes, whereas 7 patients presented rare genomic imbalances.

Conclusion

This study showed that CNVs are present in African population and show the importance to implement genetic testing in East-African countries.