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Hypospadias is a birth defect of the urethra in the male that involves an abnormally placed urinary meatus (opening). Instead of opening at the tip of the glans of the penis, a hypospadic urethra opens anywhere along a line (the urethral groove) running from the tip along the underside (ventral aspect) of the shaft to the junction of the penis and scrotum or perineum. A distal hypospadias may be suspected even in an uncircumcised boy from an abnormally formed foreskin and downward tilt of the glans.
The urethral meatus opens on the glans penis in about 50-75% of cases; these are categorized as first degree hypospadias. Second degree (when the urethra opens on the shaft), and third degree (when the urethra opens on the perineum) occur in up to 20 and 30% of cases respectively. The more severe degrees are more likely to be associated with chordee, in which the phallus is incompletely separated from the perineum or is still tethered downwards by connective tissue, or with undescended testes (cryptorchidism).
Hypospadias are among the most common birth defects of the male genitalia (second to cryptorchidism), but widely varying incidences have been reported from different countries, from as low as 1 in 4000 to as high as 1 in 125 boys.
There has been some evidence that the incidence of hypospadias around the world has been increasing in recent decades. In the United States, two surveillance studies reported that the incidence had increased from about 1 in 500 total births (1 in 250 boys) in the 1970s to 1 in 250 total births (1 in 125 boys) in the 1990s. Although a slight worldwide increase in hypospadias was reported in the 1980s, studies in different countries and regions have yielded conflicting results and some registries have reported decreases.
Most occurences of hypospadias are sporadic, without inheritance or family recurrence; however, it can result from genetics (a pericentric inversion of chromosome 16). For most cases, no cause can be identified though a number of hypotheses related to inadequate androgen effect, or environmental agents interfering with androgen effect, have been offered. Among the suspected environmental agents have been various chemicals, sometimes termed endocrine disruptors, that interact with steroid receptors. Putative endocrine disruptors include phthalates, DDT, and polychlorinated biphenyls. [1] The associations are as yet uncorroborated by additional surveys or other methods. There are also indications that phthalates contained in hairspray can increase the risk by more than double if the mother is exposed to high concentrations of hairspray during pregnancy (such as workers in hair-dressing salons).[2][3]
Prenatal testosterone, converted in the genital skin to dihydrotestosterone, causes migration of skin fibroblasts to fully enclose the urethral groove in fetal males, normally resulting in an enclosed penile urethra by the second trimester of pregnancy. Failure of adequate prenatal androgen effect is therefore thought to be involved in many cases, making hypospadias a very mild form of intersex (under-virilization of a genetic male). Since postnatal androgen deficiency can only be demonstrated in a minority of cases, it has been proposed that transient deficiency of testosterone can occur during critical periods of fetal genital development, due to elevation of anti-müllerian hormone or more subtle degrees of pituitary-gonadal dysfunction. More recently, abnormalities of transcription factors have been proposed.
In animals, several teratogenic drugs or chemicals can cause hypospadias by interfering with androgen action in the embryo. Speculation that environmental agents– endocrine disruptors– might be interfering with human hormone systems has not been proven. The agents that have caused hypospadias in a small number of boys have been maternal use of synthetic progestins and finasteride in the first two trimesters of pregnancy. In 2008, it was suggested that maternal use of diethylstilbestrol, a synthetic estrogen, resulted in a 20-fold increase in prevalence of hypospadias[4] although a followup study showed the risk, though present, to be much lesser. [5]
In a minority of cases a postnatal deficiency of, or reduced sensitivity to, androgens (testosterone and dihydrotestosterone) can be demonstrated. These are often associated with a chordee, and in severe cases a residual perineal urogenital opening and small phallus. This combination of birth defects is referred to as pseudovaginal perineoscrotal hypospadias and is part of the spectrum of ambiguous genitalia. Treatment with testosterone postnatally does not close the urethra.
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