Hennekam syndrome

Hennekam syndrome is an inherited disorder that is characterized by abnormalities of the lymphatic system, which is part of both the circulatory system and the immune system. The lymphatic system is a network of vessels that transport white blood cells (lymphocytes), nutrients, and proteins in a fluid called lymph. In people with Hennekam syndrome, the lymphatic vessels are often dilated (lymphangiectasia), which can slow down the flow of lymph and cause the vessels to leak. As a result, people with this condition experience puffiness or swelling that is caused by a buildup of fluid within certain tissues (lymphedema). The affected vessels may also break open (rupture).

The lymphedema in people with Hennekam syndrome is typically present at birth and often affects the legs and genitalia. Severely affected infants may have extensive swelling caused by fluid buildup before birth (hydrops fetalis). 

People with Hennekam syndrome may have lymphangiectasia in the kidneys, lungs, and the membrane covering the heart (pericardium). Many affected infants have intestinal lymphangiectasia, which affects the vessels that transport lymph to and from the intestines. This can cause lymph to leak into the intestines, which can interfere with the absorption of proteins and other nutrients. Affected individuals may also have a buildup of lymph in the abdomen, which can cause swelling (chylous ascites). The lymphedema that is seen in individuals with Hennekam syndrome may affect one side of the body more severely than the other.

Distinctive facial features are common among people with Hennekam syndrome. Affected individuals often have a flattened appearance to the middle of the face and the bridge of the nose, puffy eyelids, widely spaced eyes (hypertelorism), low-set ears, and a small mouth with overgrowth of the gums (gingival hypertrophy). Some individuals with Hennekam syndrome have intellectual disabilities, and these can range from mild to severe. Seizures and growth delays may also occur.

The skeletal abnormalities that can be seen in people with Hennekam syndrome include a premature fusion of the skull bones (craniosynostosis), permanently bent fingers and toes (camptodactyly), and a fusion of the skin between the fingers and toes (cutaneous syndactyly). Affected individuals may also have inward- and upward-turning feet (clubfeet), a narrow upper chest that may have a sunken appearance (pectus excavatum), and an abnormal side-to-side curvature of the spine (scoliosis).

Additional features can include structural abnormalities of the heart, kidneys, or genitals; a soft out-pouching around the belly-button (umbilical hernia); hearing loss; and excessive body hair (hirsutism).

The signs and symptoms of Hennekam syndrome vary widely, even among members of the same family. Because of the potentially serious complications, the life expectancy of individuals with Hennekam syndrome also varies.