Hereditary lethal arthrogryposis (“muscle contracture”) in horses.

The research article details a study about a hereditary disorder called arthrogryposis found in four female foals of the Norwegian “Fjord Horse” breed, which was potentially passed down from their common father, a stallion named “Bingo” 1804. The disorder, mainly affecting the limbs, was mostly lethal and seems to be influenced by a dominant gene with strong or limited sex-linkage.

Introduction to the Disease

• The study focuses on a congenital (present from birth) disorder known as ‘arthrogryposis’.
• In foals, this condition refers to the inability of the young horse to move its limbs effectively due to stiff joints (‘contracture’).
• This condition was consistently observed in the hind limbs of the four female foals involved in the study.
• Other associated conditions observed were ‘polydactylia’ (having more than the usual number of digits), ‘brachygnathia superior’ (the upper jaw being shorter than the lower), and ‘cleft palate’ (an opening or gap in the roof of the mouth).

Genetic Inheritance

• The analysis suggests the disorder was likely passed down from their father, “Bingo” 1804. The stallion, even though it seemed quite normal, had produced four affected foals and four normal ones, suggesting that he carried the gene for the disorder.
• Twelve healthy foals in total were sired by “Bingo” 1804. Of these twelve, four female Fjord horse foals displayed the symptoms of arthrogryposis.
• This pattern led the researchers to believe the disorder was related to a dominant gene – a gene that masks the effect of the alternate non-dominant (recessive) gene.

Sex-Linked or Sex-Influenced Dominant Gene

• The research also highlighted the possibility of the disease being caused by a sex-limited or a strongly sex-influenced gene.
• Sex-limited traits are those where the expression of a specific trait is restricted to only one sex, even though the gene for the trait might be present in both.
• Sex-influenced traits, on the other hand, are those where males and females carry the genes for the traits, but environmental interactions such as hormones can affect the expression of these traits.
• The distribution of the disorder amongst Bingo’s offspring leads the researchers to believe that the gene causing arthrogryposis in Bingo’s offspring is potentially a sex-limited or a strongly sex-influenced dominant gene.

Lethality of the Disorder

• The study also highlights that arthrogryposis is lethal, meaning it usually leads to the death of the foals.
• While it is not explicitly mentioned why the disorder is lethal, potential reasons could include the compromised movement and feeding capabilities resulting from the condition, thereby affecting the survival chances of the foal.