Tetrasomy Y by structural rearrangement: clinical report

A mosaic karyotype of 45,X/46,X,psu idic(Y)(q12) in a ten-year-old boy: integrating high-throughput sequencing with cytogenetic technique for precise diagnosis and genetic counselling

BACKGROUND

Isodicentric Y chromosome (idic(Y)) is the most commonly reported aberration of the human Y chromosome, which is an important cause of abnormal sexual development. The breakpoints of isodicentric Y chromosome mostly occurred in Yq11.2 and Yp11.3, however, the breakpoints in Yq12 are relatively rare.

CASE PRESENTATION

We described a 10-year-old boy presenting hypospadias, micropenis and short stature, as well as unilateral cryptorchidism without normal testicular seminiferous tubules structure by biopsy. Whole exome sequencing didn't find any pathogenic/likely pathogenic variants related to phenotypes of this patient. Copy number variation sequencing showed the duplication of whole Y chromosome. Subsequently, karyotyping and FISH analyses demonstrated his genetic diagnosis was mosaic 45,X[8]/46,X,psu idic(Y)(q12)[32], with the breakpoint in Yq12.

CONCLUSIONS

Our case proved that it would be beneficial to integrate high-throughput sequencing with cytogenetic technique for precise diagnosis, treatment and genetic counselling.

Autism spectrum disorder associated with 49,XYYYY: case report and review of the literature

Background

Sex chromosome aneuploidies occur in approximately one in 420 live births. The most frequent abnormalities are 45,X (Turner syndrome), 47,XXX (triple X), 47,XXY (Klinefelter syndrome), and 47,XYY. The prevalence of males with more than one extra sex chromosome (e.g. 48,XXYY or 48,XXXY) is less common. However, the literature provides little information about the cognitive and behavioural phenotype and the natural history of the disease. We report the clinical, neurocognitive, social cognitive and psychiatric characterization of a patient with 49,XYYYY syndrome.

Case presentation

The patient presented with a complex phenotype including a particular cognitive profile with intellectual deficiency and autism spectrum disorder (ASD) with limited interests. Moreover, social anxiety disorder with selective mutism and separation anxiety disorder were observed (DSM-5 criteria, MINI Assessment).

Conclusion

It is now admitted that 49,XYYYY has unique medical, neurodevelopmental and behavioural characteristics. Interestingly, ASD is more common in groups with Y chromosome aneuploidy. This clinical report suggests that understanding the cognitive and social functioning of these patients may provide new insights into possible therapeutic strategies, as cognitive remediation or social cognitive training.

Correlation of intercentromeric distance, mosaicism, and sexual phenotype: molecular localization of breakpoints in isodicentric Y chromosomes

Isodicentric chromosomes are among the structural abnormalities of the Y chromosome that are commonly identified in patients. The simultaneous 45,X cell line that is generated in cell division due to instability of the isodicentric Y chromosome [idic(Y)] has long been hypothesized to explain the variable sexual development of these patients, although gonads have been studied in only a subset of cases. We report here on the molecular localization of breakpoints in ten patients with an idic(Y). Breakpoints were mapped by FISH using BACs; gonads and fibroblasts were also analyzed when possible to evaluate the level of mosaicism. First, we demonstrate great tissue variability in the distribution of idic(Y). Second, palindromes and direct repeats were near the breakpoint of several idic(Y), suggesting that these sequences play a role in the formation of idic(Y). Finally, our data suggest that intercentromeric distance has a negative influence on the stability of idic(Y), as a greater proportion of cells with breakage or loss of the idic(Y) were found in idic(Y) with a greater intercentromeric distance. Females had a significantly greater intercentromeric distance on their idic(Y) than did males. In conclusion, our study indicates that the Y chromosome contains sequences that are more prone to formation of isodicentric chromosomes. We also demonstrate that patients with an intercentromeric distance greater than 20 Mb on their idic(Y) are at increased risk of having a female sexual phenotype.

Effects of sex chromosome aneuploidies on brain development: evidence from neuroimaging studies

Variation in the number of sex chromosomes is a relatively common genetic condition, affecting as many as 1/400 individuals. The sex chromosome aneuploidies (SCAs) are associated with characteristic behavioral and cognitive phenotypes, although the degree to which specific individuals are affected can fall within a wide range. Understanding the effects of different dosages of sex chromosome genes on brain development may help to understand the basis for functional differences in affected individuals. It may also be informative regarding how sex chromosomes contribute to typical sexual differentiation. Studies of 47,XXY males make up the bulk of the current literature of neuroimaging studies in individuals with supernumerary sex chromosomes, with a few small studies or case reports of the other SCAs. Findings in 47,XXY males typically include decreased gray and white matter volumes, with most pronounced effects in the frontal and temporal lobes. Functional studies have shown evidence of decreased lateralization. Although the hypogonadism typically found in 47,XXY males may contribute to the decreased brain volume, the observation that 47,XXX females also show decreased brain volume in the presence of normal pubertal maturation suggests a possible direct dosage effect of X chromosome genes. Additional X chromosomes, such as in 49,XXXXY males, are associated with more markedly decreased brain volume and increased incidence of white matter hyperintensities. The limited data regarding effects of having two Y chromosomes (47,XYY) do not find significant differences in brain volume, although there are some reports of increased head size.

New techniques to understand chromosome dosage: mouse models of aneuploidy

Aberrations in human chromosome copy number and structure are common and extremely deleterious. Their downstream effects on phenotype are caused by aberrant dosage of sequences in the affected regions. However, we know little about why the abnormal gene copy number causes disease or why specific features result from deficits in specific chromosomes. Mice are the organism of choice to help us try to tease apart the complex relationships between genotype and phenotype in aneuploidy and segmental aneusomy syndromes. As new technologies such as chromosome engineering and the creation of transchromosomic mice become routine, these will help us identify individual dosage-sensitive genes that are causative in specific syndromes and will enable us to produce mouse models to accurately recapitulate human chromosomal disorders.