Hajdu-Cheney syndrome

Description

Hajdu-Cheney syndrome is a rare disorder that can affect many parts of the body, particularly the bones. Bone loss from the tips of the fingers and toes (acroosteolysis) is a characteristic feature of the condition. The fingers and toes may appear short and rounded, and they may become shorter over time as the bone continues to break down. In people with Hajdu-Cheney syndrome, the fingers are more likely to be affected than the toes. Bone loss in the fingers can interfere with fine motor skills, such as picking up small objects.

The signs and symptoms of Hajdu-Cheney syndrome vary greatly among affected individuals, even among members of the same family. Many of the disorder's features, including acroosteolysis, are not present at birth but become apparent in childhood or later.

Additional bone abnormalities are common in people with Hajdu-Cheney syndrome. Affected individuals typically develop osteoporosis, which causes the bones to be brittle and prone to fracture. Many affected individuals experience a type of fracture called a compression fracture in the spinal bones (vertebrae). Some develop an abnormal curvature of the spine (scoliosis or kyphosis). Hajdu-Cheney syndrome can also affect the shape and strength of the long bones in the arms and legs. The bone abnormalities that are associated with this condition often lead to short stature.

Hajdu-Cheney syndrome can also involve the bones of the skull. The shape of the skull is often dolichocephalic, which means it is elongated from back to front. In many affected individuals, the bone at the back of the skull bulges outward, causing a bump called a prominent occiput. Serious complications of Hajdu-Cheney syndrome include abnormalities known as platybasia and basilar invagination. Platybasia is a flattening of the base of the skull that is caused by thinning and softening of the skull bones. Basilar invagination occurs when the softened bones allow part of the spine to protrude through the opening at the bottom of the skull and push into the lower parts of the brain. These abnormalities can lead to severe neurological problems, such as a buildup of fluid in the brain (hydrocephalus) or spinal cord (syringomyelia) and breathing difficulties. In some cases, these abnormalities can be life-threatening.

Additional signs and symptoms can include a small lower jaw (micrognathia) and an opening in the roof of the mouth called a cleft palate.  Adults with Hajdu-Cheney syndrome may have facial features that are described as "coarse."  These facial features can include widely spaced and downward-slanting eyes, eyebrows that grow together in the middle (synophrys), low-set ears, and a large space between the nose and upper lip (a long philtrum).

Other features of Hajdu-Cheney syndrome can include joint abnormalities, particularly an unusually large range of joint movement (hypermobility); dental problems; hearing loss; and a deep, gravelly voice. Affected individuals may also have recurrent childhood infections, heart defects, and kidney abnormalities that include the growth of multiple fluid-filled cysts (polycystic kidneys). Some people with this condition have delayed development in childhood, but the delays are usually mild.

Frequency

Although Hajdu-Cheney syndrome is a rare disease, its exact prevalence is unknown. Fewer than 100 affected individuals have been described in the medical literature.

Causes

Hajdu-Cheney syndrome is associated with variants (also called mutations) in the NOTCH2 gene. This gene provides instructions for making a receptor protein. Other proteins, called ligands, can fit into specific sites on receptor proteins, like a key into a lock. When a ligand binds to the NOTCH2 receptor protein, it triggers a signaling pathway called the NOTCH2 signaling pathway. NOTCH2 signaling is important for the early development of bones and for bone remodeling, a normal process in which old bone is removed and new bone is created to replace it. NOTCH2 signaling also appears to be involved in the development of the heart, kidneys, teeth, and other parts of the body.

Variants in a specific area near the end of the NOTCH2 gene are associated with Hajdu-Cheney syndrome. These variants cause cells to produce a version of the NOTCH2 receptor protein that cannot be broken down normally. As a result, the protein accumulates, which leads to an increase in NOTCH2 signaling. It is unclear exactly how the buildup of NOTCH2 receptor proteins leads to the various features of Hajdu-Cheney syndrome. Researchers suspect that the skeletal features of the disorder, including acroosteolysis, osteoporosis, and the appearance of certain facial features, are a result of abnormal bone development and remodeling.

Inheritance

Hajdu-Cheney syndrome is inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to cause the disorder. Many cases of this condition result from a new (de novo) variant in the gene that occurs during the formation of reproductive cells (eggs or sperm) in an affected individual's parent or during early embryonic development. These affected individuals typically have no history of the disorder in their family.

Autosomal dominant inheritance with a new (de novo) mutation. Credit: U.S. National Library of Medicine.

Other Names for This Condition

• Acroosteolysis dominant type
• Acroosteolysis with osteoporosis and changes in skull and mandible
• Arthrodentoosteodysplasia
• Cheney syndrome
• Hajdu-cheney syndrome-notch2
• HJCYS
• Serpentine fibula polycystic kidney syndrome
• SFPKS

Where this page came from

This page was imported from MedlinePlus Genetics, National Library of Medicine. Courtesy of MedlinePlus from the National Library of Medicine; its genetics summaries and the illustrations credited to the library are in the public domain. Pictures credited to others are not copied.

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