All limb-girdle muscular dystrophies (LGMD) show a similar distribution of muscle weakness, affecting both upper arms and legs. Frequently, the first reported symptoms are difficulty climbing stairs, standing from a squatting position, or raising arms above the head.
The dominant LGMDs usually show adult onset. In addition to muscle weakness, the creatine kinase (CK) values are elevated in affected individuals usually 4 - 10 times the normal laboratory values. Currently, neither presymptomatic nor prenatal testing is available for any form of dominantly inherited limb-girdle muscular dystrophy.
The gene for LGMD 1B has been linked to chromosome 1q11-q21. This form of LGMD was linked in several families in 1997. The clinical characteristics of this form of LGMD are the age of onset is less than 20 with slow progression, beginning in the lower extremities and progressing to involve the upper extremities by age 20-30. Individuals with this form of LGMD do not develop significant contractures. The feature that separates LGMD 1B from the other forms is the association of cardiac involvement in a high percentage of individuals in the families studied. The cardiac abnormalities reported have been atrioventricular (AV) conduction disturbances and abnormal cardiac rhythms with individuals developing symptoms of abnormally slow heart rates, fainting, and sometimes death. Presymptomatic treatment has necessitated the placement of a cardiac pacemaker in some individuals. The mutation for LGMD 1B has been identified in the Lamin A/C gene on chromsome 1q. Two other syndromes which also have mutations in this gene are familial partial lipodystrophy (Köbberling-Dunnigan Syndrome) and Emery Dreifuss muscular dystrophy, type 2.