Male infertility and sperm problems
Sperm abnormalities can be due to sperm production or final maturation errors resulting in defects in sperm quantity and quality. Exposure to environmental toxins can also induce sperm abnormalities.
In the healthy male’s body, spermatozoa of various types must be present in different amounts. Spermia of the first type in a healthy representative of the stronger sex account for 70% of the total ejaculate volume. If this amount is reduced, the patient’s fertility decreases.
The complete absence of sperm in the ejaculate is a condition called azoospermia. This sperm abnormality can arise from either a complete failure in sperm production or a blockage in the sperm transport ducts preventing release of sperm in the ejaculate.
Oligospermia is a condition of abnormally low sperm numbers, defined by the World Health Organization (WHO) as less than 20 million sperm per milliliter (approximately one-quarter teaspoon) ejaculate. Infertility from oligospermia can be treated by the use of sperm injection techniques because only one sperm per egg is necessary for fertilization.
Asthenozoospermia (low sperm motility)
Asthenozoospermia is a condition in which sperm in the ejaculate are incapable of swimming (nonmotile). For sperm to be able to swim, they need a normally formed sperm tail and a power source (the mitochondria) located behind the sperm head.
Electron microscopy has discovered that sometimes the structural tubules (cilia) of the sperm tail fail to form (primary ciliary dyskinesia). Mitochondrial defects can also cause “engine failure,” resulting in nonmotile sperm.
During a process called spermiogenesis, the newly formed sperm undergoes dramatic changes in cell shape to form a functional sperm cell. The cell elongates and loses excess cytoplasm to give the sperm a streamlined form. The mitochondria, which power the cell, are relocated to the middle section (midpiece) of the cell to power the movements of the sperm tail.
Defects in morphology or shape are called teratozoospermia. Defects can be found in the shape of the sperm head, midpiece or tail. Pin head or microcephalic sperm are sperm that formed without incorporating DNA into their sperm head. Conversely, sperm can form with abnormally large heads (macrocephalic sperm). Either abnormality prevents fertilization.
Sometimes double heads or double tails form because dividing sperm cells do not completely separate during the sperm production process.
Abnormally short, kinked or curly tails may form, which cause problems with sperm propulsion.
Sometimes sperm abnormalities are not obvious to the eye, but sperm may still be functionally unable to fertilize eggs. A failure to fertilize may be due to defects at the molecular level. For instance, during normal sperm production, the sperm membrane is modified by the addition and removal of various proteins in the sperm membrane that are necessary to give sperm full functionality.
Some of these membrane modifications include the addition of molecular receptors coating the head of the sperm, which allow the sperm to bind to the egg. If these receptors are missing, sperm can’t bind to the egg for fertilization. Molecular defects in the sperm DNA can also cause sperm abnormalities.
Exposure to reactive oxygen species (free radicals) or other chemical toxins can cause the DNA in the sperm head to disintegrate, causing fertilization failures.