Clinical, histological and genetic characterization of reducing body myopathy caused by mutations in FHL1.
We recently identified the X-chromosomal four and a half LIM domain gene FHL1 as the causative gene for reducing body myopathy, a disorder characterized by progressive weakness and intracytoplasmic aggregates in muscle that exert reducing activity on menadione nitro-blue-tetrazolium (NBT). The mutations detected in FHL1 affected highly conserved zinc coordinating residues within the second LIM domain and lead to the formation of aggregates when transfected into cells. Our aim was to define the clinical and morphological phenotype of this myopathy and to assess the mutational spectrum of FHL1 mutations in reducing body myopathy in a larger cohort of patients. Patients were ascertained via the detection of reducing bodies in muscle biopsy sections stained with menadione-NBT followed by clinical, histological, ultrastructural and molecular genetic analysis. A total of 11 patients from nine families were included in this study, including seven sporadic patients with early childhood onset disease and four familial cases with later onset. Weakness in all patients was progressive, sometimes rapidly so. Respiratory failure was common and scoliosis and spinal rigidity were significant in some of the patients. Analysis of muscle biopsies confirmed the presence of aggregates of FHL1 positive material in all biopsies. In two patients in whom sequential biopsies were available the aggregate load in muscle sections appeared to increase over time. Ultrastructural analysis revealed that cytoplasmic bodies were regularly seen in conjunction with the reducing bodies. The mutations detected were exclusive to the second LIM domain of FHL1 and were found in both sporadic as well as familial cases of reducing body myopathy. Six of the nine mutations affected the crucial zinc coordinating residue histidine 123. All mutations in this residue were de novo and were associated with a severe clinical course, in particular in one male patient (H123Q). Mutations in the zinc coordinating residue cysteine 153 were associated with a milder phenotype and were seen in the familial cases in which the boys were still more severely affected compared to their mothers. We expect the mild end of the spectrum to significantly expand in the future. On the severe end of the spectrum we define reducing body myopathy as a progressive disease with early, but not necessarily congenital onset, distinguishing this condition from the classic essentially non-progressive congenital myopathies.
Schessl
Joachim
J
Division of Neurology, The Children's Hospital of Philadelphia, Pennsylvania Muscle Institute, University of Pennsylvania School of Medicine, Philadelphia, PA, USA.
Taratuto
Ana L
AL
Sewry
Caroline
C
Battini
Roberta
R
Chin
Steven S
SS
Maiti
Baijayanta
B
Dubrovsky
Alberto L
AL
Erro
Marcela G
MG
Espada
Graciela
G
Robertella
Monica
M
Saccoliti
Maria
M
Olmos
Patricia
P
Bridges
Leslie R
LR
Standring
Peter
P
Hu
Ying
Y
Zou
Yaqun
Y
Swoboda
Kathryn J
KJ
Scavina
Mena
M
Goebel
Hans-Hilmar
HH
Mitchell
Christina A
CA
Flanigan
Kevin M
KM
Muntoni
Francesco
F
Bönnemann
Carsten G
CG
D000328:Adult; D002648:Child; D002675:Child, Preschool; D005260:Female; D040181:Genetic Diseases, X-Linked / Q000235:genetics*; D020022:Genetic Predisposition to Disease; D006801:Humans; D007223:Infant; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics*; D060588:LIM Domain Proteins; D008297:Male; D016253:Microscopy, Immunoelectron; D009124:Muscle Proteins / Q000235:genetics*; D018482:Muscle, Skeletal / Q000473:pathology; D009135:Muscular Diseases / Q000235:genetics* / Q000473:pathology; D020125:Mutation, Missense; D010375:Pedigree
C101149:FHL1 protein, human; D047908:Intracellular Signaling Peptides and Proteins; D060588:LIM Domain Proteins; D009124:Muscle Proteins