Although researchers have been able to establish a clear syndrome with characteristic or “core” symptoms, much about the disorder is not fully understood. Several factors including the small number of identified cases, the lack of large clinical studies, and the possibility of other genes influencing the disorder prevent physicians from developing a complete picture of the potential associated symptoms and prognosis. Therefore, it is important to note that affected individuals may not have all the symptoms discussed below. Parents should talk to their children’s physician and medical team about their specific case, associated symptoms and overall prognosis.
Infants with pycnodysostosis may experience delayed closure of the sutures of the skull. An infant’s skull has seven bones and several joints called sutures. Sutures are made of tough, elastic fibrous tissue and separate the bones from one another. Sutures meet up (intersect) at two spots on the skull called fontanelles, which are better known as an infant’s “soft spots”. The seven bones of an infant’s skull usually fuse together until around age two or later. In infants with pycnodysostosis, the sutures take longer to fuse together, which can affect the proper development of the skull. The skull is often larger than normal.
Distinctive facial features are common and include an abnormally prominent forehead (frontal bossing), a pointed nose, a highly-arched roof of the mouth (palate), prominent eyes with blue discoloration to the whites of the eyes (bluish sclerae), and a small jaw due to underdevelopment of the bones of the jaw (hypoplasia of the maxilla and mandible). Affected individuals may have several dental problems including delayed eruption of baby (deciduous) teeth, and then persistence of these teeth after they come in. They also experience delayed eruption of the permanent teeth. Some individuals may be missing teeth because the teeth fail to develop (hypodontia).
Individuals with pycnodysostosis may also have malformation of the collarbone (clavicular dysplasia) and breakdown of bone (osteolysis), particularly the outermost bones of the fingers and toes (acroosteolysis). The fingers may be small and stubby, and the fingernails may be absent or abnormally small. People with pycnodysostosis experience abnormal hardening and density of bone (osteosclerosis). Osteosclerosis causes bone to be fragile and affected individuals are prone to repeated fractures with minimal trauma or without trauma (spontaneously). The legs are most commonly affected by fracturing. Some people may have abnormal curvature of the spine such as having an s-shaped spine (scoliosis). Lower Back Pain due to stress fractures of the lower spinal bones (vertebrae) can occur. There may be deformities of chest development, which can cause breathing (respiratory) issues. Some individuals may snore, while others may have sleep apnea. Sleep apnea is a condition where a person will momentarily stop breathing during sleep. Sometimes, Sleep apnea can be severe.
Some individuals with pycnodysostosis have growth hormone deficiency and deficiency of another hormone called insulin-like growth factor 1 (IGF-1), which also plays a role in growth during childhood. Affected individuals reach an adult height that is shorter than would otherwise be expected (short stature). The arms and legs of affected individuals are usually abnormally short.
Less often, pycnodysostosis may occur with other symptoms such as loose (lax) joints, underdevelopment (hypoplasia) of the sinuses, enlargement of the liver and spleen (hepatosplenomegaly), and underdevelopment of the pituitary gland.