64,XX sex reversal syndrome in a Spanish purebred horse

MIGUEL MORENO MILLÁN; GABRIEL ANAYA; MONIKA BUGNO PONIEWIERZKA; SEBASTIÁN DEMYDA PEYRÁS

Ischia

Conferencia; 21th International Colloquium on animal cytogenetic and gene mapping; 2014

ICACGM

Abnormal morphologies in horses are related in most of the cases to atypical chromosomal complements. An higher percentage of these horses are characterized as animals with unspecified sex or with disorders in the sexual development (DSD). We studied the case of a three years old Spanish Purebred horse submitted to karyotiping due to its abnormal sexual morphology. On physical examination, the animal showed an abnormal foreskin, two prominent nipples, a tight scrotum and retained testicles. His sexual behavior and libido were normal for a male horse. The animal was castrated at two years of age and the pathological study showed no abnormal tissue. The animal was karyotyped using conventional citogenetic techniques (chromosome counting and C-banding) and in situ fluorescent hybridization with two specific WCPP for ECAX and ECAY chromosomes showing a female 64,XX chromosomal complement. The presence of three different genes linked to sex chromosomal in the blood DNA of the horse was studied using PCR. Resulting in a positive amplification for ZFX and AMX and no amplification of the SRY, ZFY and AMY genes. Four different microsattelitte makers linked to the ECAX chromosome were analysed to determine the number of chromosomal copies. The genotyping of LEX 026, TKY38, TKY270 and LEX003 showed two different alleles in each marker, denoting the presence of at least two different ECAX chromosomes. All the molecular studies were repeated using DNA obtained from hair follicles to discard the presence of a blood chimerism case. The results were identical than those obtained previously. Based on our results we diagnosed the horse as a 64,XX SRY negative DSD carrying a male-like genitalia. To our knowledge, this is the second time that this kind of abnormality was reported in the Andalusian horses and the first time showing this kind of morphological abnormalities. At the present time, the cause of this abnormal sexual development remains certainly unknown. However, the most accepted theory is the occurrence of an androgen exposure during sexual development of the embryo leading to the masculinization of the female foetus. Finally, we suggest the use of genetic and cytogenetic diagnostic tools in the veterinary practice as a valuable tool to determine the origin of reproductive failures among horses.