Heterotaxy Syndrome Awareness Day Date in the current year: May 4, 2026

Heterotaxy, also known as situs ambiguus, is a rare birth defect involving an abnormal arrangement of the internal organs in the chest and abdomen. It most commonly affects the heart, lungs, liver, intestines, spleen, and other organs.

While our bodies are mostly symmetrical on the outside, our unpaired internal organs are arranged asymmetrically inside the chest and abdomen. The heart, stomach, spleen, and aorta are on the left, and the liver, gallbladder, and inferior vena cava are on the right. The lungs are also asymmetrical; the left lung has two lobes, while the right lung has three.

The normal position of the internal organs in the chest and abdomen is called situs solitus. In about one in ten thousand people, these organs are mirrored from their normal positions, a condition called situs inversus. In people with situs inversus, the left-right patterning is intact but reversed. Situs ambiguus (heterotaxy) differs from situs inversus in that organ placement is irregular and does not follow the left-right pattern.

Heterotaxy can be caused by mutations in many different genes. It may occur on its own or as part of another genetic syndrome. Research indicates that certain maternal factors during pregnancy may increase a child’s risk of developing heterotaxy syndrome, including diabetes mellitus, smoking, and exposure to chemicals such as pesticides, organic solvents, and ingredients in some hair dyes. In some individuals with heterotaxy syndrome, the cause of the condition is unknown.

Unlike situs inversus, which is often asymptomatic, heterotaxy can cause severe health problems. It can alter the structure of the heart, resulting in multiple heart defects. The lungs’ structure can also be altered, resulting in breathing difficulties. Patients with heterotaxy may lack a spleen (asplenia) or have multiple small, poorly functioning spleens (polysplenia). Other possible defects include biliary atresia and intestinal malrotation.

The severity of the condition depends on which organs are affected and what abnormalities are present. Mild cases of heterotaxy are less common, not because they are rare, but because they may be underdiagnosed. In all cases involving heart defects, symptoms usually appear at birth or soon after. These symptoms include difficulty breathing and feeding, cyanosis (a blue tint to the lips, skin and nails due to a lack of oxygen), and lethargy.

Patients with severe heterotaxy-related defects usually require surgery to repair the affected organs. Patients with asplenia are immunocompromised and at high risk for infection, so infection prevention is critical. Even after successful surgeries, patients require lifelong monitoring and supportive care from a team of specialists, including cardiologists, pulmonologists, gastroenterologists, and immunologists.

Heterotaxy Syndrome Awareness Day, established in 2014, aims to raise awareness of this rare condition and provide affected families with resources and support. The day also pays tribute to deceased heterotaxy patients and honors doctors, researchers, and others who have worked to improve patients’ lives and find better treatments.