New research shows that a genital deformity called hypospadias is on the rise
in baby boys, and some experts wonder if hormone-disrupting chemicals could be
to blame. Hypospadias is a birth defect in which the urethra, the tube that
carries urine, does not exit at the tip of the penis. It may instead exit on
the underside of the penis or in the scrotum. While the cause of the defect is
unknown, hormones seem to play a crucial role.
A study by the Centers for Disease Control and Prevention (CDC) in Atlanta
showed a doubling in hypospadias rates across the United States in recent
decades. The condition now affects approximately 1 out of every 125 males born
in this country, making it one of the most common genital anomalies in baby
boys. The CDC study, which appeared in the November 1997 issue of the journal
Pediatrics, sparked concern in the scientific and medical communities.
Hypospadias results from incomplete development of the urethra, and can cause
problems in both urination and sexual function. The abnormal location of the
urethral opening ("pee-hole") can result in deviation of the urine stream and
urine spraying. In severe cases the boy is forced to sit down to urinate.
Later in life, sexual function may be hampered if the abnormality restricts
semen delivery. Other problems include curvature of the penis and
psychological stress due to the abnormal appearance of the genitals.
Disrupted hormone signaling may contribute to the defect. A boy's urethra
forms when two folds of skin fuse to form a tube during embryonic development.
Testosterone is crucial for this event, which takes place between weeks 8 and
12 of gestation. The fusion is similar to zipping up a sleeping bag: the two
sides of the urethra "zip" together, leaving a hollow tube inside. Incomplete
fusion can leave a hole further down the shaft of the penis in an abnormal
spot. Clinical studies show that some boys with hypospadias have defects in
their testosterone metabolism or testosterone receptors. This suggests that
hypospadias can result from altered levels of the sex hormones that guide
development of the genitalia.
Surgery to correct the problem is highly successful, and can usually be
accomplished with a single operation. The best time to perform the operation
is when the baby is between 6 and 15 months of age. The recent CDC study is
the first to report an increase in hypospadias outside of Europe. To track the
occurrence of hypospadias over time, CDC scientistsused information from two
independent birth defects monitoring programs: one local, and one nationwide.
The local program is known as the Metropolitan Atlanta Congenital Defects
Program (MACDP). Between 1968 and 1993, the program recorded hypospadias rates
in newborns at 22 hospitals and clinics in the Atlanta, Georgia area. It also
noted the degree of hypospadias, from mild to severe. The other program, the
Birth Defects Monitoring Program (BDMP), provided rates from a collection of
hospitals throughout the country between 1970 and 1993. This nationwide data
allowed researchers to compare the occurrence of hypospadias in the four census
regions of the United States: West, Central, Southeast and Northeast.
Data from both programs showed an approximate doubling in hypospadias rates
during the 1970s and 80s. Rates increased markedly in all four regions of the
U.S., according to BDMP data. It was during this same time period, in the
mid-80s, that European birth defects registries also reported upward trends in
hypospadias.
Furthermore, MACDP data showed an increase in the occurrence of severe cases.
Over the time period studied, severe hypospadias took up a greater and greater
proportion of all reported cases. This makes it unlikely that the increase in
hypospadias is simply a result of increased reporting of mild cases by
physicians. If mild cases were being reported in greater numbers, the ratio of
mild to severe cases would increase over time. Instead, the CDC saw a decrease
in that ratio.
The cause of the increase in hypospadias is unknown, and CDC researchers are
reluctant to speculate. However, some members of the scientific community feel
that hormone-disrupting contaminants in our environment could play a role.
Chemicals that mimic estrogen, or block testosterone, could alter the hormone
signals needed for normal development of the genitalia. That hypothesis will
need to be tested with further research.
Paulozzi LJ, et al. (1997). "Hypospadias Trends in Two US Surveillance
Systems". Pediatrics 100(5):831-834.
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