Laminin-α2 (merosin), β-dystroglycan, α-sarcoglycan (adhalin), and dystrophin expression in congenital muscular dystrophies: An immunohistochemical study1

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Abstract

Muscle biopsies of 13 congenital muscular dystrophy (CMD) patients were investigated for the expression of laminin-α2 (merosin), β-dystroglycan, α-sarcoglycan (adhalin) and dystrophin. Expression of these proteins was normal in six out of eight patients with pure-CMD, in three non-Japanese patients clinically resembling Fukuyama-CMD (F-CMD), and in two patients with Walker–Warburg syndrome (WWS). The two ‘pure’-CMD patients with white matter hypodensity showed severely decreased laminin-α2 expression and normal expression of the other proteins. Our findings in the non-Japanese patients, clinically resembling F-CMD, are different from those in Japanese cases with F-CMD in the literature. Consequently, our patients suffer from WWS or from another yet undetermined form of CMD.

Introduction

According to two European Neuromuscular Centre (ENMC) workshops 3, 4, the congenital muscular dystrophies (CMDs) can be classified into classical or pure-CMD with only muscle involvement, including a subtype with white matter hypodensity, Fukuyama type CMD (F-CMD) with both muscle and structural brain abnormalities and CMD with muscle, eye and brain abnormalities or muscle–eye–brain disease (MEB-D), including the Finnish type (F-MEB-D) and the more severe Walker–Warburg syndrome (WWS). All F-CMD and most F-MEB-D cases were observed in Japan and Finland, respectively.

Muscle fibres are surrounded by a specialized extracellular matrix—the basement membrane (BM)—that contains laminin-2 (an isoform of laminin-1), type IV collagen, fibronectin and heparin–sulphate proteoglycan. The BM plays a major role in muscle development and regeneration, in signal transmission, nerve adhesion and in distribution and transmission of force. Laminin-2 is a cross-shaped protein with a large chain (laminin-α2 or merosin) and two smaller side chains (laminin-β1 and laminin-γ1); the large chain is encoded by chromosome 6 [25]. In muscle, laminin-2 is found around intra- and extrafusal muscle fibres and nerves (Schwann cells).

Besides laminin-2, laminin-1 may be discerned. Laminin-1 also contains a large chain (encoded by chromosome 18) and two smaller chains (laminin-β1 and laminin-γ1). In muscle, laminin-1 is found around capillaries and regenerating muscle fibres [5].

The BM of muscle fibres is linked to subsarcolemmal dystrophin via a transmembrane dystrophin-associated–glycoprotein (DAG) complex. This complex (Fig. 1) is composed of a dystroglycan and a sarcoglycan subcomplex. The dystroglycan subcomplex consists of two proteins (α- and β-dystroglycan) that are encoded by the same gene [8]located on chromosome 3 [9]. Laminin-α2 is bound to α-dystroglyan (a 156 kDa glycoprotein [8]) at the outer side of the sarcolemma. Deficiency of laminin-α2 causes disruption of the muscle BM [15]. The sarcoglycan subcomplex consists of α-, β-, γ- and δ-sarcoglycan, with respective molecular weights of 50, 43, 35 and 25 kDa. Apparently, an intact dystrophin—DAG—laminin complex is an essential condition for normal muscular function. Dystrophin absence and abnormalities are found in X-linked recessive Duchenne dystrophy and Becker type dystrophy. Deficiency of α-sarcoglycan or adhalin (gene located on chromosome 17 [18]) is found in severe childhood autosomal recessive muscular dystrophy or SCARMD [13].

Recently, many pure-CMD patients were shown to be laminin-α2 negative 19, 20. The absence of laminin-α2 expression appeared to correlate with white matter hypodensities on magnetic resonance imaging (MRI) in ‘pure’-CMD patients 14, 20, 24.

In F-CMD, a severe reduction of laminin-α2 [5], β-dystroglycan and α-sarcoglycan [12]was observed.

In this paper, we will present and discuss our results concerning the immuno-detection of laminin-α2, β-dystroglycan, α-sarcoglycan and dystrophin in 13 patients with various types of CMD.

Section snippets

Patients and methods

The muscle biopsies of 13 patients were investigated; these 13 CMD patients comprised of eight pure-CMD patients (six patients without and two with white matter hypodensities), three non-Japanese patients clinically resembling F-CMD (further denoted as ‘F-CMD’) and two patients with WWS. The clinical and morphological data are summarized in Table 1Table 2.

Unfixed frozen sections of the biopsies were immunohistochemically stained in order to detect laminin-α2, β-dystroglycan, α-sarcoglycan and

Results

Laminin-α2 expression was present around intra- and extrafusal muscle fibres and nerves (the Schwann cells). The staining was regular and intense in six out of eight pure-CMD patients; in the two other pure-CMD patients (patients 7 and 8, the patients with white matter hypodensity) laminin-α2 staining was markedly decreased (Table 2, Fig. 2A); Schwann cells and muscle spindles were not present. Laminin-α2 staining was normal in the three non-Japanese ‘F-CMD’ patients (Table 2, Fig. 2D) and in

Discussion

Our patients with markedly decreased laminin-α2 expression were cases of pure-CMD with diffuse white matter abnormalities, which is in agreement with other literature 14, 20, 24.

Laminin-α2 gene locus and laminin-α2 deficient CMD were shown to be closely linked [7]. The primary role of laminin-α2 in this disease was genetically stated in two families [6]. Our two patients may represent cases with a defective gene since they closely resemble the linked cases.

Unfortunately, no Schwann cells and

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    • Cited by (0)

    1

    This study is part of the research programme ‘Disorders of the Neuromuscular system’ of the University of Nijmegen.

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