Cytogenetic and genetic studies in a hypospadic horse (Equus caballus, 2n = 64).

The study involves a 4-year-old Friesian breed horse presenting with hypospadias, a condition causing ventral penis deviation. Despite the horse exhibiting normal development and libido, a detailed cytogenetic and genetic investigation revealed certain anomalies in one telomere of its chromosome 1 and a mutation in the MAMLD1 gene.

Cytogenetic Investigation

• The scientists used a variety of techniques including Chromosome Banding Analysis (CBA), Reverse Banding Analysis (RBA), Silver-Nucleolar Organizer Region Staining (Ag-NOR), and Fluorescent In Situ Hybridization (FISH) with telomere Peptide Nucleic Acid (PNA) probes. These techniques were used to analyze the karyotype of the horse, observing the structure and composition of its chromosomes.
• The horse’s chromosomes were found to have a normal male arrangement (2n = 64,XY). However, one telomere (the end part of a chromosome which protects it from deterioration or from fusing with neighboring chromosomes) of the horse chromosome 1 (ECA 1) was found to be shorter than its counterpart and also those of a normal/control horse.

Genetic Investigation

• The researchers also studied the sequences of two specific genes: SRY and MAMLD1. The SRY (Sex determining Region Y) gene plays a crucial role in male sexual development, while the MAMLD1 (Mastermind-Like Domain 1) is associated with hypospadias in humans.
• The SRY gene sequence was found to be normal, indicating that the gene didn’t contribute to the hypospadias condition in the horse.
• A mutation was, however, observed in the MAMLD1 gene sequence. The change was homozygous (i.e. the mutation was inherited from both parents), changing a cytosine (C) to adenine (A). This change led to the production of an isoleucine amino acid instead of a leucine in the protein developed from the gene sequence.
• Although the mutation was detected, the researchers caution that it is challenging to establish a direct correlation between hypospadias and this genetic change in the horse.

Significance of the Study

• This study represents the first detailed cytogenetic and genetic investigation on a horse with hypospadias. While the findings shed some light on possible genetic influencers of the condition, the authors emphasize that more research is needed to understand and substantiate these initial findings.