Y-autosome translocations

Epidemiology and Etiology:

· Typically de novo

· Carriers are usually infertile

· 70% involve an acrocentric chromosome

· Usually heterochromatin from Yq12 to an acrocentric short arm (p11-p13)

· Half involve chromosome 15

· Homology between heterochromatic blocks in 15p and Yq

· Males and females can be carriers

· Other

Common sites:

·

Gross features:

·

Histologic features:

·

Immunophenotype:

Marker:

Sensitivity:

Specificity:

Molecular features:

· 3 azoospermia factor regions

· AZFa

· AZFb

· AZFc

Other features:

· Parent with a Y-autosome translocation:

· Yqh-acrocentric translocation

· No clinical significance

· Theoretical risk of UPD 15, not to be overstated

· Infertility in men

· interference with sex vesicle formation

· Disrupting meiosis

· Spermatic arrest at the pachytene stage with subsequent degeneration of the spermatocytes

· Some exceptions exist:

· Y-acrocentric translocation involving heterochromatin and acrocentric short arm

· Yq heterochromatin to tip of another autosome – may or may not have reproductive implications

· Intracytoplasmic sperm injection (ICSI) makes biological paternity possible

· Preimplantation chromosome analysis allows unbalanced embryos to be discarded

· Y-acrocentric translocation p arm to p arm with oligospermia

· Most sperm that actually made it to maturity (85%) had a balanced complement

· Even some autosomal translocations can interfere with sex vesicle formation

· Those involving an acrocentric

· 45,X male

· A cryptic translocation of the SRY gene onto an autosome

· Azoospermia usually

· Loss of secondary pseudoautosomal region (PAR2) on distal Yq seems to be without phenotypic consequence

References:

· Gardner RJM, Sutherland GR. Chromosome abnormalities and genetic counseling. Oxford University Press; 2004.