Autosomal trisomy in a Thoroughbred colt: 65,XY,+31.

The research article investigates a case of autosomal trisomy in a Thoroughbred colt, detailing the severe congenital defects it caused in the colt’s musculoskeletal, urogenital, and nervous systems.

Research Context

• The research investigates autosomal trisomies in the domestic horse, Equus caballus. An autosomal trisomy is a form of genetic disorder characterized by an individual having three copies of one chromosome instead of the standard two.
• Prior to this case, there had been a few reported instances of autosomal trisomies in horses which resulted in only mild developmental defects. The chromosome involved varied across the cases, including 28, 23, 26, and 30 and the defects ranged from small size and reproductive anomalies to limb deformities.
• The case in this research is unique as it presents a new autosomal trisomy (65,XY,+31) in a Thoroughbred colt, implying three copies of chromosome 31.

Case Description and Clinical Examination

• The subject of this study was a male Thoroughbred foal, born to a 26-year-old dam.
• Upon birth, the foal had no suck reflex and required help to stand. It showed signs of dysmaturity, including small size for its age and breed, fine hair coat, and loose flexor tendons in the hind limbs.
• Several physical abnormalities were observed such as brachygnathia inferior (an underbite condition), limb deformities, malformation of the prepuce (skin which covers the penis), displaced anus, and moist umbilicus.
• The colt also suffered from a mild form of leucopenia (reduced white blood cell count), and significant alterations in its levels of potassium, sodium, chloride, and calcium, indicating systemic issues.

Treatment Administered

• The foal received treatment which included lactated Ringer’s solution, potassium penicillin, gentamicin, cimetidine, and sucralphate.
• Its umbilicus was disinfected and the front limbs were splinted. This treatment helped the foal to stand on its own within 24 hours, although it still needed assistance in getting up.
• Despite the inferior brachygnathism (an underbite), the rehydrated foal was able to drink a milk replacer from a bowl, as its sucking ability was compromised.

Follow-Up and Observations

• Following the initial treatment, particularly the splinting, there was a partial improvement in the flexor contracture (abnormal shortening of a muscle or tendon).
• However, it became apparent that the foal had a left-sided head tilt, and when blindfolded, it had difficulties in locating walls and ended up circling in one direction.
• No further treatment of the angular limb deformities and residual contracture was pursued as the client declined.

The investigation of this case expands our understanding of autosomal trisomies in horses, particularly by revealing a new variation involving chromosome 31 and its severe effects on the animal.