Limb girdle muscular dystrophy due to LAMA2 gene mutations: new mutations expand the clinical spectrum of a still challenging diagnosis

Abstract

Mutations in LAMA2 gene, encoding merosin, are generally responsible of a severe congenital-onset muscular dystrophy (CMD type 1A) characterized by severe weakness, merosin absence at muscle analysis and white matter alterations at brain Magnetic Resonance Imaging (MRI). Recently, LAMA2 mutations have been acknowledged as responsible of LGMD R23, despite only few cases with slowly progressive adult-onset and partial merosin deficiency have been reported. We describe 5 independent Italian subjects presenting with progressive limb girdle muscular weakness, brain white matter abnormalities, merosin deficiency and LAMA2 gene mutations. We detected 7 different mutations, 6 of which are new. All patients showed normal psicomotor development and slowly progressive weakness with onset spanning from childhood to forties. Creatin-kinase levels were moderately elevated. One patient showed dilated cardiomyopathy. Muscle MRI allowed to evaluate the degree and pattern of muscular involvement in all patients. Brain MRI was fundamental in order to address and/or support the molecular diagnosis, showing typical widespread white matter hyperintensity in T2-weighted sequences. Interestingly these alterations were associated with central nervous system involvement in 3 patients who presented epilepsy and migraine. Muscle biopsy commonly but not necessarily revealed dystrophic features. Western-blot was usually more accurate than immunohystochemical analysis in detecting merosin deficiency. The description of these cases further enlarges the clinical spectrum of LAMA2-related disorders. Moreover, it supports the inclusion of LGMD R23 in the new classification of LGMD. The central nervous system involvement was fundamental to address the diagnosis and should be always included in the diagnostic work-up of undiagnosed LGMD.

Keywords: LAMA2 gene; brain MRI; leukoencephalopathy; limb girdle muscular dystrophy; merosin; muscle MRI.

Figure 1.

Muscle biopsy Patient I. (A) Haematoxylin and eosin (H&E), 40x: few fibres with internal nuclei and fibre splittings; (B) Reduced nicotinamide adenine dinucleotide dehydrogenase- tetrazolium reductase (NADH-TR), 25x, showing mild variation in fibre size. Immunolabelling of laminin alfa2 to 80 kDa fragment in a control muscle (C) and in our case (D), showing a partial protein expression in some areas of the sarcolemma (arrows). (Immunolabelling with amino-terminus antibody is not shown).

Figure 2.

Brain MRI showing diffuse abnormal high signal intensity involving peri and sovra-ventricular white matter in axial T2 images (patient I: A-B; patient III: E; patient II: F) and coronal T2 FLAIR images (patient I: C-D).

Figure 3.

Western-blot analysis. Merosin Western-blot analysis showing a severe deficiency with monoclonal MAb1922 antibody.

Figure 4.

Muscle MRI. Axial TSE T1 images of the thighs (A-B) and of the right arm (C-D) of patient I, showing a diffuse atrophy and hyperintensity signal, as for fatty degeneration; some muscles were selectively spared, in particular the deltoid, the sartorius, the gracilis, the rectus femoris and the short head of the biceps femoris; the left thigh semitendinosus muscle was partially spared too. Axial T1 images of the thighs (E) and legs (F) of patient III, showing diffuse fibro-fatty substitution of the gluteal muscles, of the posterior thigh, adductor magnus and of the quadriceps; milder connective substitution in the medial gastrocnemious bilaterally.

Figure 5.

Muscle biopsy Patient III. Hematoxilin and Eosin stain on the the first muscle biopsy (A) and on the second (B). Scattered hypotrophic fibers in (A). Dystrophic pattern showing necrosis, nuclei centralizations and increase in connective tissue (B). Immunofluorescence staining (Merosin antibody) on the first muscle biopsy (C) and on the second (D). Original Magnification 40X (Merosin Laminin Alpha2). Normal Merosin binding (C) and scattered mild Merosin reduction of binding (D).

Suppl. Figure 1.

Pedigree of patient II suggesting a pseudo-dominant inheritance.