Cleidocranial dysplasia (CCD) spectrum disorder is a skeletal dysplasia that represents a clinical continuum ranging from classic CCD (triad of delayed closure of the cranial sutures, hypoplastic or aplastic clavicles, and dental abnormalities) to mild CCD to isolated dental anomalies without the skeletal features. Most individuals come to diagnosis because they have classic features. At birth, affected individuals typically have abnormally large, wide-open fontanelles that may remain open throughout life. Clavicular hypoplasia can result in narrow, sloping shoulders that can be opposed at the midline. Moderate short stature may be observed, with most affected individuals being shorter than their unaffected sibs. Dental anomalies may include supernumerary teeth, eruption failure of the permanent teeth, and presence of the second permanent molar with the primary dentition. Individuals with CCD spectrum disorder are at increased risk of developing recurrent sinus infections, recurrent ear infections leading to conductive hearing loss, and upper-airway obstruction. Intelligence is typically normal.

Pyle disease is characterized by long bones with wide and expanded trabecular metaphyses, thin cortical bone, and bone fragility. Fractures are common in Pyle disease, and fracture lines usually go through the abnormally wide metaphyses, revealing their fragility (summary by Kiper et al., 2016).

Aspartylglucosaminuria (AGU) is a severe autosomal recessive lysosomal storage disorder that involves the central nervous system and causes skeletal abnormalities as well as connective tissue lesions. The most characteristic feature is progressive mental retardation. The disorder is caused by deficient activity of the lysosomal enzyme glycosylasparaginase, which results in body fluid and tissue accumulation of a series of glycoasparagines, i.e., glycoconjugates with an aspartylglucosamine moiety at the reducing end. AGU belongs to the group of disorders commonly referred to as the Finnish disease heritage (summary by Mononen et al., 1993 and Arvio and Arvio, 2002).

Mulibrey nanism (MUL) is a rare autosomal recessive growth disorder with prenatal onset, including occasional progressive cardiomyopathy, characteristic facial features, failure of sexual maturation, insulin resistance with type 2 diabetes, and an increased risk for Wilms tumor (summary by Hamalainen et al., 2006).

X-linked intellectual disability-craniofacioskeletal syndrome is a rare, hereditary, syndromic intellectual disability characterized by craniofacial and skeletal abnormalities in association with mild intellectual disability in females and early postnatal lethality in males. In addition to mild cognitive impairment, females present with microcephaly, short stature, skeletal features and extra temporal lobe gyrus. In males, intrauterine growth impairment, cardiac and urogenital anomalies have been reported.

A distinct syndromic type of frontonasal malformation with characteristics of hypertelorism, wide nasal bridge, broad columella, widened philtrum, widely separated narrow nares, poor development of nasal tip, midline notch of the upper alveolus, columella base swellings and a low hairline. Additional features reported in some include upper eyelid ptosis and midline dermoid cysts of craniofacial structures and philtral pits or rugose folding behind the ears.