First wild XXY house mice

Area of Science:

• Genetics and Evolutionary Biology
• Mammalian Genetics
• Reproductive Biology

Background:

• The XXY karyotype, known as Klinefelter syndrome in humans, has been documented in various mammal species.
• Laboratory mice (Mus musculus) with the XXY condition are established biomedical models.
• Despite extensive karyotyping of wild house mice, no wild XXY individuals have been previously reported.

Purpose of the Study:

• To report the extraordinary discovery of two wild house mice with an XXY karyotype.
• To describe the phenotype of these wild XXY individuals.
• To compare the incidence of the XXY anomaly in wild mice with laboratory mice and humans.

Main Methods:

• Karyotyping of wild-caught house mice from northern Italy.
• Phenotypic observation and analysis of two wild XXY male mice.
• Comparison of findings with existing data on laboratory XXY mice and human XXY individuals.

Main Results:

• Two wild male house mice with an XXY karyotype were identified in northern Italy in 2008.
• One XXY male possessed a standard karyotype (2n=40), the other had the Cremona metacentric population karyotype (2n=22).
• Both wild XXY males exhibited normal body mass and appearance but had significantly smaller testes and lacked visible germ cells, consistent with laboratory XXY mice.

Conclusions:

• The discovery of wild XXY house mice is extraordinary and expands our understanding of mammalian aneuploidy.
• The phenotypic characteristics of wild XXY mice align with those observed in laboratory models.
• The incidence of the XXY anomaly in wild mice (0.08%) falls between that of laboratory mice (0.04%) and humans (0.2%).