Phenotypic and immunohistochemical characterization of sarcoglycanopathies

Abstract

Introduction: Limb-girdle muscular dystrophy presents with heterogeneous clinical and molecular features. The primary characteristic of this disorder is proximal muscular weakness with variable age of onset, speed of progression, and intensity of symptoms. Sarcoglycanopathies, which are a subgroup of the limb-girdle muscular dystrophies, are caused by mutations in sarcoglycan genes. Mutations in these genes cause secondary deficiencies in other proteins, due to the instability of the dystrophin-glycoprotein complex. Therefore, determining the etiology of a given sarcoglycanopathy requires costly and occasionally inaccessible molecular methods.

Objective: The aim of this study was to identify phenotypic differences among limb-girdle muscular dystrophy patients who were grouped according to the immunohistochemical phenotypes for the four sarcoglycans.

Methods: To identify phenotypic differences among patients with different types of sarcoglycanopathies, a questionnaire was used and the muscle strength and range of motion of nine joints in 45 patients recruited from the Department of Neurology--HC-FMUSP (Clinics Hospital of the Faculty of Medicine of the University of São Paulo) were evaluated. The findings obtained from these analyses were compared with the results of the immunohistochemical findings.

Results: The patients were divided into the following groups based on the immunohistochemical findings: α-sarcoglycanopathies (16 patients), β-sarcoglycanopathies (1 patient), γ-sarcoglycanopathies (5 patients), and nonsarcoglycanopathies (23 patients). The muscle strength analysis revealed significant differences for both upper and lower limb muscles, particularly the shoulder and hip muscles, as expected. No pattern of joint contractures was found among the four groups analyzed, even within the same family. However, a high frequency of tiptoe gait was observed in patients with α-sarcoglycanopathies, while calf pseudo-hypertrophy was most common in patients with non-sarcoglycanopathies. The α-sarcoglycanopathy patients presented with more severe muscle weakness than did γ-sarcoglycanopathy patients.

Conclusion: The clinical differences observed in this study, which were associated with the immunohistochemical findings, may help to prioritize the mutational investigation of sarcoglycan genes.

Figure 1

Patterns of immunohistochemical findings in the non-SGP, α-SGP, γ-SGP, and β-SGP groups. Non-SGP: positive staining for all four of the sarcoglycans; α-SGP: α-sarcoglycanopathy; γ-SGP: γ-sarcoglycanopathy; β-SGP: β-sarcoglycanopathy.

Figure 2

Immunohistochemical preparations for alpha, gamma, beta and delta sarcoglycans (α-, γ-, β- and δ-SG, respectively). (A) A representative non-SGP case showing positive reactions for all four SGs; (B) a representative case of α-SGP showing no expression of α-SG and positive reactions for the remaining SGs; (C) a representative case classified as α-SGP showing patchy expression of all four SGs with lower expression of α-SG; and (D) a representative case of γ-SGP showing a negative reaction for γ-SG and positive staining for the other three SGs. 200x magnification. SG: sarcoglycan; SGP: sarcoglycanopathy.

Figure 3

Histograms illustrating the clinical findings. First, the percentage of patients in each group presenting with a tiptoe gait pattern are shown. The Kruskal-Wallis test showed a significant difference between the α-SGP and γ-SGP groups (p = 0.03). Second, the percentage of patients in each group with calf pseudo-hypertrophy is shown. The Kruskal-Wallis test showed a significant difference between the α-SGP and γ-SGP groups (p = 0.02). Third, the maximum motor ability of the groups is shown. 37.5% of the patients with an α-SG deficiency were confined to a wheelchair, while only 12% of the patients with a γ-SG deficiency and none of the non-SGP patients were wheelchair bound. non-SGP: positive staining for all sarcoglycans; α-SGP: α-sarcoglycanopathy; γ-SGP: γ-sarcoglycanopathy; A: ambulant; AA: ambulant with aid; W: confined to a wheelchair.

Figure 4

Graphs illustrating the differences found among the three groups from the comparative analysis of the muscle strength scores of the shoulders and upper limbs (A) and of the hips and lower limbs (B) (* p<0.05; ** p<0.01; *** p<0.001). non-SGP: positive staining for all sarcoglycans; α-SGP: α-sarcoglycanopathy; γ-SGP: γ-sarcoglycanopathy.