- Discussion:
    - autosomal dominant disorder which occurs as a result of a mutation of a calmodulin like calcium binding protein;
    - result is abnormal proteoglycan accumulation in the chondrocyte rough endoplasmic reticulum;
    - there are moderate to severe epiphyseal, metaphyseal, and physeal abnormalities in long bones, as well as spinal involvement;
    - subtypes:
            - four subtypes have been proposed: two with autosomal inheritance (I, III) and two with recessive inheritance (II, IV);
            - there will be variable severity of skeletal involvement (type I is often mild vs type IV which is the most severe);

- Clinical Features:
    - condition is not recognized at birth, but growth retardation is apparent by the age of 2 or 3 years;
           - at that time, rhizomelic shortening of the extremities is evident;
    - dwarfism can easily be differentiated from achondroplasia by the normal face and skull, and the absence of interpedicular narrowing of the lumbar spine;
           - face and head have normal appearance & trunk is normal except for exaggerated lumbar lordosis;
    - adult height ranges from 106 to 130 cm.
    - extremities:
           - long bones are characterized by epiphyseal, metaphyseal, and physeal changes;
                  - this uneven growth leads to joint incongruity and malalignment;
           - precocious arthritis is a major complication, as in other epiphyseal dysplasias;
           - coxa vara is relatively mild but may lead to deformity, lateral subluxation, and incongruity;
    - spine:
           - cervical spine atlantoaxial instability may occur and is worked up in the usual manner (flexion and extension views);
                  - atlantoaxial fusion is procedure of choice if instability causes symptoms;
           - progressive thoracolumbar kyphosis may occur but is much less severe than that seen in achondroplasia;
                  - angular or vertebral wedging or kyphosis may result from several less involved vertebral bodies

Pseudoachondroplasia: Biochemical and histochemical studies of cartilage. 

Disorders of the Pediatric and Adolescent Spine.  Spinal Manifestations of Skeletal Dysplasias.