A 64,X,i(Xq) karyotype in a standardbred filly.

This research paper discusses the presence of the 64,X,i(Xq) karyotype in a standardbred filly, which is unusual based on the typical chromosomal abnormalities encountered in equine veterinary practice. Chromosome analysis is typically only used in cases of suspected infertility or subfertility in mares.

Chromosomal Analysis in Equine Practice

• Despite not being a routine procedure, chromosomal analysis is recommended for mares that are infertile or subfertile and have small, inactive ovaries.
• Typically, the most common abnormalities noted in such mares relate to sex chromosomes, including patterns such as 63,XO and mosaic 63,XO/64,XX, which result in sterile mares, and 64,XY, which leads to conditions like gonadal dysgenesis, sex reversal, and testicular feminisation.

Phenotypic Effects of Chromosomal Abnormalities in Horses

• Compared to humans, the physical manifestations of these chromosomal abnormalities in horses are relatively mild.
• This subtlety in the physical expression of genetic abnormalities may be why veterinarians don’t regularly suspect chromosomal irregularities in horses.

Aberration of the X Chromosome in Humans and Horses

• In humans, an isochromosome of the long arm of the X, known as i(X), is a frequently observed structural aberration.
• Such an anomaly is often associated with Turner’s syndrome, which presents with symptoms like short stature and amenorrhoea.
• However, in horses, there have been no reported cases of i(X) presence, which could largely be due to the small numbers of cases that have so far been studied.