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Skeletal dysplasias are generalized disorders of bone and/or
cartilage that can produce short stature, osseous deformity, and
functional disabilities. More than 372 different genetic disorders
of the skeleton have been described by the International Skeletal
Dysplasia Society as constitutional diseases of bone1;
collectively, dysplasias represent most of the intrinsic disorders
of bone with the dysostoses comprising the rest. The overall frequency
of the skeletal dysplasias is about 1 in 4000 births,2 making
this class of disorders about as common as neurofibromatosis type
1 or Turner syndrome, conditions much better known to the pediatric practitioner.
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Skeletal dysplasias have traditionally been divided into the
disorders that primarily affect the growth of cartilage and bone,
the chondrodystrophies (eg, achondroplasia) and disorders with primary
abnormalities of bone that lead to defects in bone density or mineralization
(eg, the osteogenesis imperfectas).1,3 Included
in the former group are a special class of disorders caused by disorganized
development of skeletal components with multiple cartilaginous exostoses,
fibrodysplasia ossificans progressiva being the proteotypic syndrome.
The dysostoses or disorders of bone structure that cause malformations
and functional abnormalities of individual bones are also encompassed
under the broader categorization of genetic skeletal disorders. Over
the past decade, the distinction between these groups has become
increasingly blurred and some mutations can cause abnormalities
of bone and cartilage that affect various skeletal elements.1
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Skeletal dysplasias can cause substantial morbidity in children
and adults, yet many affected individuals lead relatively normal
lives, albeit with some special challenges. Historically, the term dwarf has
been used to refer to persons with bone dysplasias and disproportionate
short stature. Because of the pejorative nature of this label and
because it evokes thoughts of a different class of personhood, the
use of the term is discouraged. The preferred terminology is to
refer to a condition by its medical designation (eg, diastrophic
dysplasia); however, the term dwarfism as a medical
term is still widely used and accepted by many. This section describes
the classification, distinguishing characteristics, and management
of selected disorders.
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Conventionally, the skeletal dysplasias are often grouped according
to the anatomic location of the bones that are most severely affected
and the histologic abnormalities that are commonly observed. For
example, skeletal dysplasias that affect the spine and the epiphyses
are called spondyloepiphyseal dysplasias. However,
the criteria used to categorize disorders into this classification
are inconsistently applied to many skeletal dysplasias (eg, achondroplasia),
and this diminishes its heuristic value. The classification schemes
used to organize dysostoses are quite varied. No single system has
become widely adopted,1,3 and, accordingly, the
clinical presentation and varied expressions of the dysostoses tend
to be difficult to remember accurately.
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The strategy of classifying malformations according to the developmental
pathway that is disrupted can be applied to the skeletal dysplasias.1,3 The
logic of the classification is to separate development of the skeleton
into three primary phases: patterning, ...