Osteochondrodysplasias

Synonyms: skeletal dysplasia, osteochondrodystrophy

What are the osteochondrodysplasias?¹

The skeletal dysplasias (osteochondrodysplasias) are a heterogeneous group of more than 350 disorders characterised by abnormalities of cartilage and bone growth resulting in abnormal shape and size of the skeleton and disproportion of the long bones, spine, and head. They are frequently associated with orthopaedic complications and varying degrees of short stature. They also can be associated with a variety of orthopaedic, neurological, auditory, visual, pulmonary, cardiac, renal, and psychological complications.

Osteochondrodysplasias include:

• Usually fatal: achondrogenesis, thanatophoric dysplasia, short rib polydactyly (Majewski and Saldino-Noonan type), homozygous achondroplasia, osteopetrosis (congenital), camptomelic dysplasia, dys-segmental dysplasia (Silverman-Handmaker type), osteogenesis imperfecta type II, hypophosphatasia (congenital), chondrodysplasia (rhizomelic).

• Often fatal: asphyxiating thoracic dystrophy (Jeune's syndrome).

• Occasionally fatal: Ellis-van Creveld syndrome, diastrophic dysplasia, metatropic dwarfism, Kniest's dysplasia.

How common are osteochondrodysplasias? (Epidemiology)¹

• Although each skeletal dysplasia is relatively rare, collectively the birth incidence of these disorders is almost 1/5000.

• The birth prevalence of lethal neonatal short limb skeletal dysplasias may be approximately 1 in 9000 births.²

• The 4 most common skeletal dysplasias are thanatophoric dysplasia, achondroplasia, osteogenesis imperfecta, and achondrogenesis.

• Thanatophoric dysplasia and achondrogenesis account for 62% of all lethal skeletal dysplasias. Achondroplasia is the most common non-lethal skeletal dysplasia.

Osteochondrodysplasias symptoms (presentation)¹

Skeletal dysplasias are usually evident in the newborn period or during infancy but some disorders do not present until later in childhood. Disproportionate short limbs should be considered if arms do not reach the mid pelvis in infancy or upper thigh later. Maternal hydramnios is probably the most significant event associated with fetal skeletal dysplasia during pregnancy. Features include:

• Disproportionately short stature (short limbs or short trunk).

• Disproportionate shortening may be:
  

  • Short proximal segments - humerus, femur: eg, achondroplasia, hypochondroplasia, spondyloepiphyseal dysplasia congenita, diastrophic dysplasia, and congenital short femur.

  • Short middle segments - radius, ulna, tibia, fibula: eg, Langer and Nievergelt types of mesomelic dysplasias, Robinow's syndrome, Reinhardt-Pfeiffer syndrome.

  • Short distal segments - metacarpals, phalanges: eg, acrodysostosis and peripheral dysostosis.

  • Short middle and distal segments - forearms, hands: eg, acromesomelic dysplasia.

  • Shortening of extremities involving an entire limb: eg, achondrogenesis, fibrochondrogenesis, dys-segmental dysplasia, Roberts' syndrome.

  • Short trunk (short neck, small chest and protruding abdomen): eg, Morquio's syndrome, metatrophic dysplasia, spondylo-epimetaphyseal dysplasia.

• Other features may include:
  

  • Delayed motor milestones.

  • Airway obstruction.

  • Pain, deformity and neurological deficits caused by spinal disorders.

• Other skeletal anomalies include large head with hydrocephalus, and bowlegs with waddling gaits.

• There are different neurological, cardiovascular and many other specific abnormalities associated with specific osteochondrodysplasias.

Differential diagnosis

• If short stature is proportional, the condition may be due to endocrine or metabolic disorders, or chromosomal or non-skeletal dysplasia genetic defects.

• In general, patients with disproportionately short stature have osteochondrodysplasia.

See also the article on Short Stature.

Investigations¹

Osteochondrodysplasias are diagnosed on the basis of clinical, imaging and molecular criteria.

• Skeletal survey to assess the whole dysplastic skeleton.

• Various biochemical, haematological and immune function tests depending on the osteochondrodysplasia and individual patient context.

• Further assessments will include ultrasound, CT and/or MRI scan, echocardiogram.

• Molecular studies and cytogenetic studies.

Treatment³

To provide a highly specialised multidisciplinary approach, these treatments are usually managed by specialised centres.

There are very few treatments for skeletal dysplasia and therapy is largely supportive at present. However, the last few decades have been marked by the identification of numerous genes implicated in genetic disorders, helping in the elucidation of the underlying pathophysiology of skeletal dysplasias. This has allowed the potential for new therapeutic approaches such as cellular therapy, gene therapy, or pharmacological therapy for various conditions.

Babies with certain disorders diagnosed antenatally, such as achondroplasia, should be delivered by Caesarean section.

Symptomatic treatments include orthopaedic interventions such as spinal fusion, bone lengthening and also use of a brace, eg, for kyphosis.

Respiratory complications can be complex and are characterised by airway anomalies, restrictive lung disease due to a narrow and abnormally compliant chest wall, pulmonary hypoplasia, and central apnoea.⁴

Bone marrow transplantation may benefit patients with skeletal dysplasia associated with congenital immune deficiencies, mucopolysaccharidosis, lipidosis, osteopetrosis, and Gaucher's disease.

Prognosis¹

• Prognosis depends on the precise nature of the specific osteochondrodysplasia.

• These disorders range in severity from precocious arthropathy in relatively average stature individuals to severe dwarfism with perinatal mortality.