Diagnosis
(a)Clinical picture, laboratory tests
(b)EMG (electromyography)
(c) Muscle MRI/CT
(d)Muscle biopsy
(e)Genetic analysis
(a) In typical cases, the diagnosis of LGMD2A can be suspected on the basis of the clinical picture (see below). When a person suffers from muscle weakness, with characteristic distribution to the girdles (shoulders and pelvis), with winged scapulae, difficulty in lifting arms, lifting weights, climbing stairs, getting up from the ground, running and there is a finding of elevated creatine phosphokinase or CPK (frequent in these forms), the suspicion of a calpain-deficient girdle dystrophy arises easily. CK is elevated (up to 80 times the normal value) particularly during the early stages of the disease and in the preclinical phase (less than 10 years of life).
The recurrence of similar cases in a family may point to a type of recessive genetic transmission and therefore easily point to an LGMD2A picture. However, it should be kept in mind that a diagnosis of LGMD2A can be reached even when only the casual finding of asymptomatic CPK elevation is present (14% of cases, with a male to female ratio of 3:1).
(b) On electromyographic (EMG) examination, there are signs of intrinsic muscle distress.
(c) The use of diagnostic imaging techniques-such as CT or muscle MRI-may be of further help in orienting toward one form of LGMD rather than another (e.g., in LGMD2A there may be atrophy, i.e., reduction in muscle mass, early in the thigh adductor, semimembranosus, and vastus intermedius muscles with relative sparing of the vastus alteralis, sartorius, and gracilis muscles).
(d) In the context of diagnostic examinations, great importance is given to the muscle biopsy that highlights the presence of a degeneration of the muscle tissue (necrotic fibers, nuclear centralization, fibers in regeneration, increased endomysial connective tissue, possible presence of inflammatory infiltrate). It is important to try to assay calpain by investigation of western blot, which by identifying the absence or reduction of the 94 kDa band (CAPN3) represents the gold standard for diagnosing LGMD2A. Subjects with a total or severe absence of calpain have a higher probability of being carriers of the calpain gene mutation than those with only a partial deficiency.
Partial reduction of calpain 3 alone may indeed occur in other dystrophies (LGMD1C, 2B, 2I, 2J) as a side effect.
In addition, the finding of a normal amount of calpain does not rule out the diagnosis, however, as the protein may be present but not functioning properly.
e) Genetic analysis results in the final examination to confirm the diagnosis in order to identify the mutation on the calpain 3 gene specifically responsible for the LGMD2A form.
In the Italian population, 36% of Italian patients with LGMD phenotype with severe proximal muscle involvement (shoulders and pelvis) have calpain 3 gene mutation, confirming that calpain 3 deficiency represents, also in our population, the first cause of cingulate dystrophy.
Debut
LGMD2A has a variable onset from early childhood to adulthood with a range between 2 and 45 years and a median between 15 and 20 years; in 71% of cases the age of onset is between 8 and 18 years. Early onset cases are before 12 years of age, late onset cases are after 30 years of age.
Clinical course
Although the course is inexorably progressive, there is a variability in clinical presentation (related to the age of onset and the age of gait loss) ranging from asymptomatic forms (1%), mild to severe phenotypes with early onset. Patients on average are able to walk on their own until the age of 30-35 years with symptoms of different severity even among affected siblings, generally walking is lost 10-30 years after onset.
A more rapid evolution was observed in males compared to females so it has been hypothesized that estrogen may modulate the mechanism of action of calpain 3, this should be kept in mind for possible future treatments
The spectrum of events includes the following areas:
Skeletal muscle
Muscle weakness associated with atrophy - usually localized at the pelvic and scapulohumeral level-is a characteristic of calpainopathy and often allows its clinical diagnosis. However, it can present with such variability that distinct clinical forms can be defined (see below). The impairment is symmetrical and progressive; in most patients at onset the proximal lower limbs (pelvis) are more affected than the upper limbs (scapular girdle).
Next, the gluteus maximus, hip adductors, and, to a lesser extent, the knee flexors are affected, whereas the abductors are relatively spared. Compared with the involvement of the posterior thigh ligament muscles, the knee extensor muscles may appear selectively spared. Finally, involvement of the anterior tibial muscles is more delayed. Hypertrophy of the gastrocnemius in early cases, which can be observed in the early stages of the disease, associated with elevated CPK values, may mistakenly point to a form of dystrophinopathy (a picture similar to Becker's muscular dystrophy) The earlier impairment of the pelvic girdle means that initially one complains of difficulty in climbing stairs, getting up from the ground, running; the later involvement of the anterior tibial muscles leads to a difficult dorsiflexion of the foot with difficulty in walking on the heels.
In the upper girdle, which is generally involved later than the pelvic-femoral girdle, the latissimus dorsi, rhomboid, serratus anterior, and pectoralis major muscles are primitively affected, resulting in disconnection and elevation of the scapulae (winged scapulae in 83% of cases, symmetrical), similar to those observed in the course of facio-scapulo-humeral dystrophy, resulting in difficulty in lifting arms or lifting weights.
In the upper extremities, then, the biceps and brachioradialis are affected early, whereas the triceps brachii (arm extension) is preserved.
Of note is some laxity of the abdominal muscles (from involvement of the rete muscles of the abdomen) and early lumbar hyperlordosis.
The facial, extraocular, and pharyngeal muscles are usually spared.
With time, muscular-tendinous retractions generally appear, responsible for skeletal contractures and deformities (especially at the ankles with walking on the toes and difficulty in walking on the heels), but also at the elbows, wrist and knees. They are usually late, but evolve rapidly after loss of gait.
Scoliosis is also described (in cases with earlier onset).
Possible rigidrachid.
Heart
Cardiac impairment is rare, although calpain 3 is consistently expressed in the fetal heart. Cardiac conduction disturbances have been reported in rare cases. Usually, since these are adult patients, they may be prone to age-related cardiovascular disease (hypertension, coronary artery disease, etc.).
Respiratory system
The respiratory system is generally not compromised. Vital capacity is usually preserved, rarely there is an FVC (forced vital capacity) value <80% of theoretical; nocturnal hypoventilation is not described
Central Nervous System
Cognitive-intellectual functions are normal or mild mental retardation.
The following clinical variants are described
Pelvi-femoral cingular shape
Onset between 13 and 29 years of age. The earliest symptoms consist of weakness in the pelvic-femoral girdle muscles, with difficulty in climbing stairs, getting up from the floor and running fast. Symptoms related to muscle weakness of the upper limbs are usually later, but in any case the scapular girdle is also involved. Loss of gait occurs 10-30 years after onset, in most cases after the age of 40. This is the most typical and frequent variant.
More severe early-onset cingular form
In the early onset/infantile forms (under 12 years of age) the course is more rapid with earlier loss of gait and more marked retraction of the muscles and tendons. Early motor milestones are generally normal, although affected children sometimes appear less strong than their peers.
Atypical clinical pictures (patients with Duchenne muscular dystrophy-like picture, with muscle-tendon retractions similar to those observed in Emery-Dreifuss dystrophy, or with pseudometabolic phenotype characterized by muscle stiffness and myalgia) are present in 25% of cases.
Late-onset cingular phenotype
Onset over 30 years of age, weakness predominantly localized to the pelvic girdle.
Scapulohumeral shape
In 10% of cases, the condition begins with weakness of the scapular girdle between the ages of 16 and 37 years; after some time, the deficit extends to the other girdle. This is a less frequent and more benign form than pelvis-femoral.
Miyoshi type shape
Atypical impairment distal to the lower limbs (feet) and subsequent involvement of the gluteal and thigh muscles. This picture is more typically related to forms with dysferlin deficiency with which it goes in differential diagnosis.
Asymptomatic form
Asymptomatic cases, presenting only modest CPK elevation, are described.
Depending on the clinical picture presented, LGMD2A may go into differential diagnosis with another form of autosomal recessive cingulate dystrophy, FKRP-deficient LGMD2I, or with facio scapulohumeral dystrophy, FSHD, in forms with scapulohumeral presentation.