Introduction
The lower limbs or lower extremities are part of the body that includes the leg, foot, and ankle. Legs are used for standing, walking, running, and giving support to the body. Legs are one of the most basic necessities for the human body, as any defect in the lower limbs can affect an individual normal lifestyle. Sometimes the deformity in lower limbs is due to certain genetic disorders, and one such condition is known as sirenomelia.
What Is Sirenomelia?
Sirenomelia or mermaid syndrome is a rare congenital disorder that is characterized by fused limbs, which is why the term mermaid syndrome is given. It occurs in infants or newborns. Additional malformations like gastrointestinal abnormalities, underdeveloped kidneys, and pelvis anomalies can also occur. Males are generally affected more than females by the ratio of 2.7 to 1. It is a rare syndrome, and one in 60,000 to 100,000 births is affected by sirenomelia. In twins, the frequency of sirenomelia is greater in identical (monozygotic) than fraternal (dizygotic) twins.
What Are the Factors That Can Cause Sirenomelia?
The exact cause of sirenomelia is not clear to date, but researchers have concluded that both environmental and genetic factors play an essential role in the development of this disorder.
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In some cases, sirenomelia results due to irregular development of the circulating blood system (disruption in the vascular system) within the embryo. Some affected cases have only one artery arising from the abdominal cavity rather than the usual two arteries (which normally help in carrying the blood to the caudal or rearward tail end of the embryo). The single artery (also known as the steal vessel as it steals the blood from the embryo’s lower portion) misdirects the blood flow to the placenta without going through the caudal end of the embryo. Along with this, the steel vessel does not let the nutrients reach the embryo. Due to all this, the lower limbs are not able to form properly, and the embryo fails to divide into two legs.
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Some environmental causes that can lead to sirenomelia include alcohol, cigarettes, exposure to other toxins like cocaine, and amino acid imbalances. According to research, these environmental factors have a teratogenic effect. A teratogen is a substance that disrupts the embryo’s development.
What Are the Symptoms of Sirenomelia?
The signs and symptoms of sirenomelia are visible in the first year of life. Some of the common symptoms include:
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Complete fusion of the lower limbs.
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The affected individual has only one limb (the long bone of the thigh).
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Back of the foot facing forward.
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Urogenital abnormalities such as the absence of one of the kidneys or an absent bladder.
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Abnormal front-to-back curvature of the spine.
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Heart malformations.
What Are the Risk Factors for Sirenomelia?
Sirenomelia risk factors could include the following:
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The biological mother having diabetes, which is true in 22 percent of fetuses with this illness (it is possible that the risk can be decreased by the mother maintaining adequate blood glucose management).
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Exposure to teratogens, which are elements that raise the possibility of birth defects.
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Having a mother who is under 20 years old.
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Genetic influences.
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Being a man, as the illness affects men 2.7 times more frequently than women.
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Being an identical twin – of the 300 cases of sirenomelia that have been documented in medical publications, 15 percent are twins, primarily identical twins.
What Are the Different Modalities Through Which Sirenomelia Can Be Diagnosed?
In newborns, the defects are clinically visible. The patient’s complete medical and family history is taken by a doctor. A fetal ultrasound is done to confirm the diagnosis during the second trimester.
Fetal Ultrasound: A fetal ultrasound helps in detecting any malformation or defects related to sirenomelia. It is an imaging technique that uses sound waves to form an image of the fetus. The healthcare professional will apply a gel on the mother’s abdomen as it helps in the improved conduction of sound waves. The transducer is moved around the abdomen to see the sirenomelia disorder to scan the image. The procedure is painless and is completed in less than half an hour.
What Are the Differential Diagnosis of Sirenomelia?
The differential diagnosis includes the following:
Amelia - It is a condition that has similar symptoms as sirenomelia. Amelia is a congenital disorder in which the lower limb is absent due to a particular gene mutation.
Caudal Regression Syndrome - It is a disorder in which the lower half of the body is impaired due to genetic or environmental causes. The symptoms are similar to sirenomelia and are often confused for the same.
How Is Sirenomelia Managed?
It is a rare disorder that is usually fatal past the newborn phase. There is complete monitoring needed for infants born with this condition by coordinated efforts of specialists like cardiologists, pediatricians, surgeons, and orthopedists.
Surgical Treatment: In many cases, the fused legs are successfully separated through surgery successfully. Balloon-like tissue expanders are inserted under the child’s skin during the surgery. The balloon is filled with a salt solution for a particular amount of time, and eventually, the skin stretches and grows. Once the legs are separated, the excess skin is used to cover the divided portion of the legs.
What Is the Prognosis for Those Suffering from Sirenomelia?
It is often fatal at the newborn stage because it frequently results in various organ abnormalities, particularly those of the heart and lungs.
However, some infants may live longer if it primarily affects the legs rather than other body parts (especially the kidneys).
Conclusion
Sirenomelia is a rare congenital disorder in which a child is born with fused lower limbs, which is also called mermaid syndrome. It is a fatal condition but can be easily diagnosed during the second trimester with the help of fetal ultrasound. There are not many treatment modalities for this condition, but with the help of surgical intervention, the legs can be separated. Proper care and regular doctor visits will help understand the condition more clearly.
