A rare reciprocal translocation (12;21) segregating for nine generations

Area of Science:

• Human Genetics
• Population Genetics
• Reproductive Genetics

Background:

• Autosomal reciprocal translocations can increase the risk of reproductive issues, including spontaneous abortions and aneuploid offspring.
• The specific (12;21) translocation has been observed in families with adverse reproductive outcomes.

Purpose of the Study:

• To investigate the prevalence and potential common ancestry of the (12;21) autosomal reciprocal translocation in Finnish families.
• To assess the reproductive implications, such as spontaneous abortions and Down syndrome, associated with this translocation.

Main Methods:

• Karyotyping to identify the autosomal reciprocal translocation (12;21).
• Genealogical tracing using Finnish population registries to establish family relationships and common ancestry.
• Statistical analysis comparing reproductive outcomes between translocation carriers and non-carriers.

Main Results:

• The (12;21) translocation was identified in five Finnish families, with three experiencing recurrent spontaneous abortions and two having a child with Down syndrome.
• Genealogical research indicated a common ancestor born in 1752 for four of the families, suggesting a shared origin for the translocation.
• The translocation segregated similarly to normal chromosomes, with a statistically insignificant but potentially clinically significant increase in spontaneous abortions observed in carrier matings.

Conclusions:

• The (12;21) autosomal reciprocal translocation in these Finnish families likely originates from a common ancestor.
• Accurate genetic counseling can be provided for families carrying this specific translocation, considering the observed reproductive risks.