Proteomic identification of FHL1 as the protein mutated in human reducing body myopathy

Abstract

Reducing body myopathy (RBM) is a rare disorder causing progressive muscular weakness characterized by aggresome-like inclusions in the myofibrils. Identification of genes responsible for RBM by traditional genetic approaches has been impossible due to the frequently sporadic occurrence in affected patients and small family sizes. As an alternative approach to gene identification, we used laser microdissection of intracytoplasmic inclusions identified in patient muscle biopsies, followed by nanoflow liquid chromatography-tandem mass spectrometry and proteomic analysis. The most prominent component of the inclusions was the Xq26.3-encoded four and a half LIM domain 1 (FHL1) protein, expressed predominantly in skeletal but also in cardiac muscle. Mutational analysis identified 4 FHL1 mutations in 2 sporadic unrelated females and in 2 families with severely affected boys and less-affected mothers. Transfection of kidney COS-7 and skeletal muscle C2C12 cells with mutant FHL1 induced the formation of aggresome-like inclusions that incorporated both mutant and wild-type FHL1 and trapped other proteins in a dominant-negative manner. Thus, a novel laser microdissection/proteomics approach has helped identify both inherited and de novo mutations in FHL1, thereby defining a new X-linked protein aggregation disorder of muscle.

Phenotypic heterogeneity in British patients with a founder mutation in the FHL1 gene

“…Immunohistochemical analysis of RBM patients' muscle indicated that clinical severity might be correlated with the amount of residual FHL1 protein, and differential reduction in FHL1 amount was also observed in affected males and females from a SPM family with FHL1 mutation. 10,12 Unfortunately, the amount of FHL1 protein could not be assessed on muscle biopsies from our patients and further studies are warranted.…”

“…[9][10][11][12][13][14][15][16][17]21 The available genotype-phenotype data indicate that patients belonging to the 'RB subgroup' harbour missense mutations or short in-frame deletions affecting the second LIM domain, whereas mutations found in XMPMA and EDMD/ EDMD-like patients are either missense, in-frame or out-of-frame mutations localized in the more distal exons encoding the third and fourth LIM domains. 17,21 Histidine 123 and cysteine 224 appear as the main mutation hot spots for RBM and XMPMA, mutated in 7/15 and 5/9 families, respectively.…”

“…8 We first described FHL1 gene mutations in families presenting with an X-linked myopathy with postural muscle atrophy and generalized hypertrophy (XMPMA). 9 Concurrently, FHL1 gene mutations have been detected in X-linked dominant scapuloperoneal myopathy, 10,11 and subsequently in a wide spectrum of partly overlapping conditions, such as reducing body myopathy (RBM), [12][13][14] rigid spine syndrome, 15 Emery-Dreifuss muscular dystrophy (EDMD), 16 and in a single family with contractures, rigid spine, and cardiomyopathy. 17 It has been suggested to classify FHL1-related disorders into two main groups, the 'reducing body (RB) subgroup' including RBM, X-linked dominant scapuloperoneal myopathy and rigid spine syndrome, all characterized by RB at histological examination, and a second subgroup, including the XMPMA and EDMD patients, characterized by later onset and absence of RB.…”

“…17 It has been suggested to classify FHL1-related disorders into two main groups, the 'reducing body (RB) subgroup' including RBM, X-linked dominant scapuloperoneal myopathy and rigid spine syndrome, all characterized by RB at histological examination, and a second subgroup, including the XMPMA and EDMD patients, characterized by later onset and absence of RB. 12,13,16 RBM may also be seen as a condition within a larger phenotypic spectrum of protein aggregate myopathies, such as the myofibrillar myopathies. 18 Here, we report three British families with X-linked muscle diseases, one being part of our original report, 9 presenting with partly heterogeneous phenotypes but sharing the p.Phe127_Tyr128insIle mutation in the FHL1 gene and a common Xq26 haplotype.…”

Caída y descomposición de hojarasca en los bosques ribereños del manantial de Cañaverales, Guajira, Colombia

“…Por ello, la caída, descomposición y liberación de nutrientes de la hojarasca son procesos funcionales claves que pueden suministrar información esencial acerca del desarrollo fenológico, vitalidad y variación anual como reacción al clima y a otros cambios ambientales (Schessl et al, 2008). Las investigaciones en el trópico han comparado ecosistemas manejados y no intervenidos (Del Valle, 2003;Dale y Polasky, 2007) y han determinado la importancia de esta hojarasca en la creación de refugios para la conservación de la biodiversidad (Perfecto et al, 1996).…”