| Contents |
|---|
| Ovotesticular Disorder of Sexual Development |
| Summary |
| Understanding the Results |
| Disease Name and Genes |
| Inheritance |
Ovotesticular Disorder of Sexual Development
Summary
Sex determination in mammals is dependent on sex chromosome composition, with XX animals being female and XY animals being male. In the absence of the Y-chromosome male determining gene SRY, no androgen is produced in the developing gonad, and the embryo develops as a female. In the presence of the Y-chromosome male determining gene SRY, the developing gonad produces androgen, and the embryo develops as a male. De novo deletions of the SRY gene in a mosaic gonad (the consequence of somatic mutation) will result in the transmission to chromosomally male (XY) offspring of Y chromosomes that fail to initiate male development as embryos. These will develop as sterile phenotypic females.
Sterile phenotypic females are obviously unsuitable for breeding, but are otherwise healthy.
Date of Last Update: 04/04/2016
Results
Understanding the Results
Phenotypic females that are XY by karyotyping or by the discovery of lack of heterozygosity for X-linked neutral variation outside of the pseudoautosomal region are potentially affected by Ovotesticular Disorder of Sexual Development (DSD). Absence of SRY by PCR or whole genome sequencing would confirm that the horse is 64, XY, SRY-negative.
Disease Name and Genes
Ovotesticular Disorder of Sexual Development (DSD) is a term applied to phenotypic sex reversal in 64, XY individuals that test negative for the Y-linked male determining gene SRY. Infertile phenotypic females with DSD that are 64, XY karyotypically lack the SRY gene as scored by attempted PCR amplification. The precise nature of the SRY mutation is unknown, but presumed to be a deletion.
Inheritance
Ovotesticular Disorder of Sexual Development (DSD) is transmitted as a de novo mutation from stallions to their sons, who appear as phenotypic females.
Stallions with a de novo mutation resulting in a Y chromosome that lacks the male-determine gene SRY have a mosaic germ line, with some of their sperm transmitting a normal Y chromosome (here shown as Y) and some of their sperm transmitting a Y chromosome lacking SRY (here shown as Y-SRY-). Some of the sons of these stallions will be normal colts (X/Y), while some will be 46, XY, SRY-negative phenotypic females (X/Y-SRY-) that are sterile. Note that in this diagram, the stallion produces two kinds of sperm carrying the Y chromosome, either a normal Y chromosome (Y), or a Y chromosome bearing a deletion of the SRY gene (Y-SRY-). Germ line mosaicism of this type is extremely rare, and most stallions produce only sperm bearing a normal Y chromosome.
