A Turner syndrome case associated with dic(Y;22)

Area of Science:

• Genetics
• Chromosomal abnormalities
• Human genetics

Background:

• Constitutional telomeric associations are rare and their mechanisms are poorly understood.
• Turner syndrome is a condition associated with a missing or partially missing X chromosome.

Purpose of the Study:

• To investigate the underlying mechanism of a rare chromosomal abnormality in a patient with Turner syndrome.
• To propose a novel mechanism for the formation of dicentric chromosomes and mosaicism.

Main Methods:

• Karyotype analysis
• Fluorescence in situ hybridization (FISH)
• Single nucleotide polymorphism (SNP) microarray analysis

Main Results:

• A female patient with Turner syndrome presented with a complex mosaic karyotype involving a dicentric (Y;22) chromosome.
• SNP microarray analysis indicated mosaic loss of heterozygosity at the pseudoautosomal regions of sex chromosomes but not on chromosome 22.
• FISH confirmed the presence of a dicentric (Y;22) chromosome with SRY and DYZ1 signals.

Conclusions:

• The separation of the dicentric (Y;22) chromosome likely led to the loss of chromosome Y without affecting chromosome 22, resulting in unique mosaicism.
• Unstable telomeric associations are hypothesized as the origin of the dicentric (Y;22) chromosome.
• A novel "pulled apart" mechanism is proposed to explain the observed chromosomal abnormality and mosaicism.