1. Two novel FHL1 gene mutations extending the phenotypic spectrum
(Ref: OMIM )
Strehle EM
Johnson K
Rakocevic-
Stojanovic V
Peric S
Milenkovic S
Farrugia ME
Longman C
Straub V
Introduction
The FHL1 gene encodes the Four and a half LIM domains protein 1. LIM domains were first identified in the Lin11, Isl-1 and Mec-3 proteins. They consist of pairs of zinc finger domains which contain 4 cysteine molecules and 1 zinc atom each. LIM proteins are important for cytoskeletal arrangements, cell growth and protein interactions. FHL1 protein is highly expressed in skeletal and cardiac muscle. FHL1 gene mutations have been linked to Emery-Dreyfuss muscular dystrophy type 6 (300696), myopathy with postural muscle atrophy (300696), reducing body myopathy 1a and 1b ( and ), and scapuloperoneal myopathy (300695). Their inheritance pattern is X-linked recessive or dominant.
Methods
Whole exome sequencing (WES) and data processing were performed by Genomics Platform at the Broad Institute of Harvard and MIT (Broad Institute, Cambridge, MA, USA). We performed whole exome sequencing on DNA samples (>250 νg of DNA, at >2 νg/μl) using Illumina exome capture (38 Mb target). Our exome-sequencing pipeline included sample plating, library preparation (2-plexing of samples per hybridization), hybrid capture, sequencing (76 bp paired reads), sample identification quality control check, and data storage. Our hybrid selection libraries cover >80% of targets at 20x and a mean target coverage of >80x. The exome sequencing data was de-multiplexed and each sample's sequence data was aggregated into a single Picard BAM file, and then analysed in detail.
Patient 1: 33-year-old ambulant female, parents and sister not affected, first symptoms aged 23, muscle weakness and wasting in legs, later in arms, severe scapular winging, hyperlordosis, ankle contractures, waddling gait, CK 650, myopathic pattern on EMG, muscle biopsy shows myopathic features and lobulated fibres, no heart and lung involvement. Mutation: FHL1 chrX T>A p.His182Gln
Patient 2: 79-year-old non-ambulant male of black Indian descent, parents not affected, adult onset, progressive upper and lower limb proximal weakness, scapular winging, arrhythmia, artificial ventilation, CK elevation >10x, myopathic and dystrophic features on muscle biopsy. Mutations: FHL1 chrX G>C p.Cys224Ser FLNC chr C>A p.Pro516Thr
Discussion
The FLNC gene on chromosome 7q32.1 encodes filamin proteins which crosslink actin filaments and connect membrane proteins with the actin-cytoskeleton. Filamin-C is expressed in cardiac and skeletal muscle. FLNC mutations are associated with autosomal-dominant familial hypertrophic (26) or restrictive (5) cardiomyopathy, distal myopathy (4) and myofibrillar myopathy (5). Treating clinicians agree that both patients fit the FHL1 phenotype. These examples highlight the value of WES in patients with unknown neuromuscular disorders.