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There’s a commonly held falsehood that men have one less rib than women. This myth may have its roots in the Bible and the creation story about Eve being made from one of Adam’s ribs.

This myth is exactly that: an unproven, untrue belief. It’s no longer held as fact by religious leaders of any denomination.

The vast majority of people are born with 12 pairs of ribs, for a total of 24, no matter their sex.

The exception to this anatomy rule are people born with specific genetic anomalies. These can take the form of too many ribs (supernumerary ribs) or too few (agenesis of ribs).

Cervical rib

Cervical rib is a genetic mutation which causes some people to be born with one or two extra ribs between the base of the neck and the collarbone.

People born with this condition may have one extra rib on either side, or one extra rib on both sides. These ribs may be fully formed bones, or they may be tissue fiber strands that don’t contain any bone.

Cervical rib is a condition that can affect any sex.

Many people who have this condition don’t have any symptoms and are unaware that they have it. Others experience discomfort, such as neck pain or numbness, caused by the cervical rib pressing down on nerve endings or blood vessels.

Cervical rib may result in a condition called thoracic outlet syndrome (TOS). TOS typically appears in adulthood and may affect more men than women. Not everyone who has cervical rib will develop TOS.

Trisomy 21 (Down syndrome)

Down syndrome is a chromosomal disorder. People born with Down syndrome sometimes have an extra rib, or a missing 12th rib. Not everyone who has Down syndrome has rib number variations.

Spondylocostal dysplasia

This rare, autosomal recessive disorder is also known as spondylocostal dysostosis. It involves an abnormal development of the ribs and spine. In addition to scoliosis and fused or misshapen vertebrae, people born with this condition may have ribs that are fused together, or missing entirely.

Spondylothoracic dysplasia

Spondylothoracic dysplasia is an autosomal recessive condition. It’s also known as spondylothoracic dysostosis. Babies born with this condition have fused ribs and fused vertebrae. They also have very small chest cavities, which can cause severe problems with breathing.

Goldenhar syndrome (oculo-auriculo-vertebral spectrum)

Goldenhar syndrome is a rare congenital condition that causes anomalies to occur in the spine, ears, and eyes.

Babies born with Goldenhar syndrome may have one or two partially formed or missing ears, and benign eye growths. They may also have an underdeveloped jaw and cheekbone, and ribs that are missing, fused, or not fully formed.

Rib abnormalities don’t need to be treated unless they cause problems, such as abnormal growth patterns, problems with breathing, or pain.

Some rib deformities may be picked up via ultrasound, before your baby is born. Others may become apparent after birth, if your baby has a smaller chest size, or displays difficulty with breathing. If so, treatment will focus on respiratory support.

Missing ribs are sometimes corrected surgically with a device called a vertical expandable prosthetic titanium rib (VEPTR). VEPTRs can be adjusted in size as your child grows.

Spinal problems such as scoliosis may be treated surgically or with a brace.

If there are no problems with posture, breathing, or walking, watchful waiting may be all that is required.

Adults with cervical ribs who start to experience symptoms associated with TOS may have their extra rib or ribs surgically removed.

The Adam and Eve story has led some people to believe that men have one fewer rib than women. This isn’t true. The vast majority of people have 12 sets, or 24 ribs, no matter their sex.

People born with certain conditions may have too many or too few ribs. These conditions don’t always require treatment. In many instances, your doctor will recommend watchful waiting.