FSHD may initially involve Weakness of muscles of the face, shoulder girdle and arms. Facial Weakness may result in limited movements of the lips, causing difficulties whistling, using a straw, or puckering the lips. Affected individuals may also develop a distinctive “mask-like” facial appearance. Upper facial Weakness may also lead to an inability to completely close the eyes during sleep.
FSHD is also typically associated with weakening and atrophy of muscles of the neck and shoulder blades and muscles at the front and back of the upper arms (biceps and triceps brachii muscles). With disease progression, there is a decrease in the ability to lift the arms due to Weakness of muscles stabilizing the shoulder blades; and “scapular winging,” one of the most common initial finding, characterized by abnormal prominence of the borders of the shoulder blades. This finding tends to become more obvious when affected individuals attempt to raise their arms to the side (laterally). In addition, when viewed from the front, the collarbones (clavicles) may appear to sag. Some affected individuals may also develop wrist drop or downward flexion of the wrist due to Weakness of certain muscles of the fingers and hands.
FSHD may also be characterized by Weakness and atrophy of other muscles, including abdominal wall, hip, and thigh muscles. Involvement of the muscle that rotates and moves the thigh outward (gluteus medius) may cause affected individuals to sway or lurch toward the affected side while walking (Trendelenburg gait). There may also be Weakness of muscles of the lower legs and feet. Such involvement may lead to a condition known as footdrop, which is characterized by an impaired ability to flex or bend the foot upward. In some affected individuals, involvement of certain muscles may result in unusually pronounced inward curvature of the lower region of the spine (lordosis) or abnormal front-to-back and sideways spinal curvature (kyphoscoliosis).
For unknown reasons, in most individuals with FSHD, the degree of Muscle Weakness may differ from one side of the body to the other (asymmetrical).
Those with the disorder may have relatively slow or moderate progression of Muscle Weakness or, in some cases, apparently non-progressive involvement of certain muscles. However, evidence suggests that the disease course is most frequently characterized by slow progression with short periods of rapid muscle deterioration. Associated Muscle Weakness may result in minimal disability or, in other people, lead to difficulties speaking; abnormalities in the manner of walking (gait disturbances); and/or an impaired ability to perform certain activities of daily living. In approximately 20% of those affected, disease progression may lead to severe Muscle Weakness that necessitates the use of a wheelchair or other mobility equipment. Families have been described in which disease manifestations ranged from minor facial Weakness in a parent to severe infantile onset in an affected child.
In some individuals with FSHD, particularly those with early onset, the disorder may also be associated with hearing impairment and/or abnormalities of blood vessels within the nerve-rich, innermost membrane of the eye (retinal vasculopathy) that may, in rare cases, lead to visual impairment.
Two types of FSHD have been described, FSHD1 (95% of those affected) and FSHD2 (5% of those affected). FSHD1 and FSHD2 have the same signs and symptoms but different genetic causes.