Diastrophic dysplasia, which is also known as disastrophic dwarfism, is a rare disorder that is present at birth (congenital). The range and severity of associated symptoms and physical findings may vary greatly from case to case. However, the disorder is often characterized by short stature and unusually short arms and legs (short-limbed dwarfism); abnormal development of bones (skeletal dysplasia) and joints (joint dysplasia) in many areas of the body; progressive abnormal curvature of the spine (scoliosis and/or kyphosis); abnormal tissue changes of the outer, visible portions of the ears (pinnae); and/or, in some cases, malformations of the head and facial (craniofacial) area.
In most infants with diastrophic dysplasia, the first bone within the body of each hand (first metacarpals) may be unusually small and "oval shaped," causing the thumbs to deviate away (abduction) from the body ("hitchhiker thumbs"). Other fingers may also be abnormally short (brachydactyly) and joints between certain bones of the fingers (proximal interphalangeal joints) may become fused (symphalangism), causing limited flexion and restricted movement of the finger joints. Affected infants also typically have severe foot deformities (talipes or "clubfeet") due to abnormal deviation and fusion of certain bones within the body of each foot (metatarsals). In addition, many children with the disorder experience limited extension, partial (subluxation) or complete dislocation, and/or permanent flexion and immobilization (contractures) of certain joints.
In most infants with diastrophic dysplasia, there is also incomplete closure of bones of the spinal column (spina bifida occulta) within the neck area and the upper portion of the back (lower cervical and upper thoracic vertebrae). In addition, during the first year of life, some affected children may begin to develop progressive abnormal sideways curvature of the spine (scoliosis). During adolescence, individuals with the disorder may also develop abnormal front-to-back curvature of the spine (kyphosis), particularly affecting vertebrae within the neck area (cervical vertebrae). In severe cases, progressive kyphosis may lead to difficulties breathing (respiratory distress). Some individuals may also be prone to experiencing partial dislocation (subluxation) of joints between the central areas (bodies) of cervical vertebrae, potentially resulting in spinal cord injury. Such injury may cause muscle weakness (paresis) or paralysis and/or life-threatening complications.
In addition, most newborns with diastrophic dysplasia have or develop abnormal fluid-filled sacs (cysts) within the outer, visible portions of the ears (pinnae). Within the first weeks of life, the pinnae become swollen and inflamed and unusually firm, thick, and abnormal in shape. Over time, the abnormal areas of tissue (lesions) may accumulate deposits of calcium salts (calcification) and eventually develop into bone (ossification). Some affected infants may also have abnormalities of the head and facial (craniofacial) area including incomplete closure of the roof of the mouth (cleft palate) and/or abnormal smallness of the jaws (micrognathia). In addition, in some affected infants, abnormalities of supportive connective tissue (cartilage) within the windpipe (trachea), voice box (larynx), and certain air passages in the lungs (bronchi) may result in collapse of these airways, causing life-threatening complications such as respiratory obstruction and difficulties breathing. In some individuals with the disorder, additional symptoms and physical findings may also be present. Diastrophic dysplasia is inherited as an autosomal recessive trait.