From GeneReviews Overview
Long QT syndrome (LQTS) is a cardiac electrophysiologic disorder, characterized by QT prolongation and T-wave abnormalities on the EKG that are associated with tachyarrhythmias, typically the ventricular tachycardia torsade de pointes (TdP). TdP is usually self-terminating, thus causing a syncopal event, the most common symptom in individuals with LQTS. Such cardiac events typically occur during exercise and emotional stress, less frequently during sleep, and usually without warning. In some instances, TdP degenerates to ventricular fibrillation and causes aborted cardiac arrest (if the individual is defibrillated) or sudden death. Approximately 50% of untreated individuals with a pathogenic variant in one of the genes associated with LQTS have symptoms, usually one to a few syncopal events. While cardiac events may occur from infancy through middle age, they are most common from the preteen years through the 20s. Some types of LQTS are associated with a phenotype extending beyond cardiac arrhythmia. In addition to the prolonged QT interval, associations include muscle weakness and facial dysmorphism in Andersen-Tawil syndrome (LQTS type 7); hand/foot, facial, and neurodevelopmental features in Timothy syndrome (LQTS type 8); and profound sensorineural hearing loss in Jervell and Lange-Nielson syndrome.

From OMIM
Although patients with mutations in the CHST3 gene may initially be given varying diagnostic labels, they have similar clinical features, including dislocation of the knees and/or hips at birth, clubfoot, elbow joint dysplasia with subluxation and limited extension, short stature, and progressive kyphosis developing in late childhood. The disorder is usually evident at birth, with short stature and multiple joint dislocations or subluxations that dominate the neonatal clinical and radiographic picture, and affected individuals may receive an initial clinical diagnosis of Larsen syndrome (see 245600) or humerospinal dysostosis. During childhood, the dislocations improve, both spontaneously and with surgical treatment, and features of spondyloepiphyseal dysplasia become apparent, leading to arthritis of the hips and spine with intervertebral disc degeneration, rigid kyphoscoliosis, and trunk shortening by late childhood; at this stage, the clinical features are those previously described as the Omani type of SED (summary by Unger et al., 2010).  http://www.omim.org/entry/143095