They are caused by an abnormal function of the lysosomal enzymes, which blocks degradation of mucopolysaccharides and leads to accumulation of harmful byproducts, namely, heparan sulfate, dermatan sulfate, and keratan sulfate. The resulting cellular malfunction can lead to a diverse array of skeletal and visceral manifestations. MPS have been subcategorized according to the type of enzyme inadequacy and glycoprotein accumulated. Cleidocranial dysostosis
Cleidocranial dysostosis is a general skeletal condition named for the collarbone (cleido-) and cranium deformities which people with it often have. Common features include:
Partly or completely missing collarbones. A soft spot or larger soft area in the top of the head where the fontanelle failed to close. Bones and joints are underdeveloped. The permanent teeth include supernumerary teeth. Permanent teeth not erupting
Bossing (bulging) of the forehead. Hypertelorism

Fibrous dysplasia
Fibrous dysplasia causes bone thinning and growths or lesions in one or more bones of the human body. These lesions are tumor-like growths that consist of replacement of the medullary bone with fibrous tissue, causing the expansion and weakening of the areas of bone involved. Especially when involving the skull or facial bones, the lesions can cause externally visible deformities. The skull is often, but not necessarily, affected, and any other bones can be involved. Langer–Giedion syndrome
Langer–Giedion syndrome is a very rare genetic disorder caused by a deletion of chromosomal material. Diagnosis is usually made at birth or in early childhood.
The features associated with this condition include mild to moderate learning difficulties, short stature, unique facial features, small head and skeletal abnormalities including bony growths projecting from the surfaces of bones. Maffucci syndrome
Maffucci syndrome is a sporadic disease characterized by the presence of multiple enchondromas associated with multiple simple or cavernous soft tissue hemangiomas. Also lymphangiomas may be apparent.Patients are normal at birth and the syndrome manifests during childhood and puberty. The enchondromas affect the extremities and their distribution is asymmetrical. Osteosclerosis
Osteosclerosis, an elevation in bone density, is normally detected on an X-ray as an area of whiteness, and is where the bone density has significantly increased. Localized osteosclerosis can be caused by injuries that compress the bone, by osteoarthritis, and osteoma. Other
Deformity type Erlenmeyer flask gives a distal femur similar to an Erlenmeyer flask. It may result from Gaucher disease. Kashin–Beck disease
Melnick–Needles syndrome
Ovine chondrodysplasia
Familial osteodysplasia, Anderson type

Diagnosis
The diagnosis is mainly based upon delineating the specific clinical and radiographic pattern of skeletal involvement. However, the different types of skeletal dysplasia can overlap considerably in their clinical presentation. Molecular or genetic analysis may be required to resolve diagnostic difficulties. Molecular analysis is also of importance to the phenotype genotype correlations and to disease classifications. Differential diagnosis
Juvenile idiopathic arthritis may closely resemble the clinical presentation of some osteochondrodysplasias or genetic skeletal dysplsias. In that, both conditions can present with swollen, stiff and deformed joints. Treatment
Emerging therapies for genetic skeletal dysplasias include  enzyme replacement therapy,  hematopoietic stem cell transplantation and  gene therapy.