Disease relevance of MYH7

• Myosin storage myopathy associated with a heterozygous missense mutation in MYH7 [1].
• The patient exhibited eccentric hypertrophy with severely impaired ejection fraction leading to heart transplantation, and carries a homozygous mutation in MYH7 (R403W) and a heterozygous variant in MYBPC3 (V896M) [2].
• MYH7 mutations caused HCM at younger age, more frequent syncope and ECG abnormalities compared with MYBPC3 mutations [3].
• The HCM patients with MYH7 mutations more often had a family history of HCM (43% vs. 29%, p = 0.006), but there was no difference in family history of sudden death (16% vs. 14%, p = NS) [4].
• OBJECTIVES: We sought to determine the prevalence and phenotype of beta-myosin heavy chain gene MYH7 mutations in a large cohort of unrelated patients with hypertrophic cardiomyopathy (HCM) [4].

High impact information on MYH7

• We previously linked Laing-type early-onset autosomal dominant distal myopathy (MPD1) to a 22-cM region of chromosome 14 [5].
• Recombinations placed the locus between framework markers D14S72 and MYH7, a 10-cM interval in which the markers D14S742, D14S50, D14S283, and TCRA showed no recombinations with the phenotype [6].
• Maximum two-point LOD scores of 2.60 at recombination fraction .00 were obtained for the markers MYH7 and D14S64--the family structure precludes a two-point LOD score > or = 3 [7].
• A multipoint analysis assuming 100% penetrance and using the markers D14S72, D14S50, MYH7, D14S64, D14S54, and D14S49 gave a LOD score of exactly 3 at MYH7 [7].
• Dinucleotide repeat polymorphisms at the P1, HBE1 and MYH7 loci [8].

Biological context of MYH7

• Cosegregation with the HCM phenotype could be demonstrated for 13 mutations (eight mutations in MYBPC3 and five mutations in MYH7) [9].
• Our previous report demonstrated that two human cardiac alpha- and beta-myosin heavy-chains (MHCs) which correspond to MYH6 and MYH7 respectively, according to Human Gene Mapping nomenclature, were mapped to human chromosome 14 and that human cardiac and skeletal MHC genes do not cosegregate [10].
• In MYH7 vs. TNNT2, mean age at diagnosis was late (P<0.03), penetrance was incomplete in adults (56 vs. 100%), and mean age at major cardiac event was higher (P<0.04) [11].
• Based on these data, the four loci were mapped within an approximately 600-kb region with the following centromere to telomere order: D14S283, D14S990, MYH6, and MYH7 [12].
• A 700-kb cosmid contig containing the D14S990 and the myosin genes and a long-range restriction map covering the region between D14S990 and the MYH6 and MYH7 gene cluster were established [12].

Anatomical context of MYH7

• MYH7 encodes the slow/beta-cardiac myosin heavy chain (MyHC), which is the main MyHC isoform in slow, oxidative, type 1 muscle fibers of skeletal muscle [1].
• The MYH7 tail domain mutation results in an inclusion body myopathy with an apparent absence of hypertrophic cardiomyopathy usually associated with mutations of this gene [13].
• Transient transfection assays demonstrated that the calcineurin/NFATc1 signaling pathway is essential for MyHCbeta promoter activation during transformation of C2C12 myotubes but is not sufficient for complete fast MyHCIId/x promoter inhibition [14].
• Along with NFATc1, myocyte enhancer factor-2D (MEF-2D) and the myogenic transcription factor MyoD transactivated the MyHCbeta promoter in calcium-ionophore-treated myotubes in a calcineurin-dependent manner [14].
• We did not detect signs of involvement of hand or finger extensors and neck muscles, seen in the original family with MPD1 [15].

Associations of MYH7 with chemical compounds

• In family MM, a 3-bp deletion in MYH7 was detected to be associated with loss of glutamic acid in position 927 (DeltaE927) of the myosin rod [16].
• Sequence analysis of the coding regions of MYH7 revealed an A-->T transversion at nucleotide position 25596 (M57965) resulting in a histidine-to-leucine amino acid change at residue 1904 (H1904L) [13].
• We report a mutation within exon eight of the MYH7 gene at a very conserved amino acid at position 232, which results in the conversion of an asparagine to serine [17].
• With a C-G transversion in nucleotide 13 619 of the MYH7 gene, located at the essential light chain interacting region in S1, the replacement of arginine by glycine took place at amino acid residue 723 [18].
• Mpd1 was disrupted by insertional mutagenesis, and the resulting mpd1 strains lacked all detectable NAD-linked mannitol 1-phosphate dehydrogenase activity (EC 1.1.1.17) [19].

Other interactions of MYH7

• Three major MyHC isoforms are expressed in human skeletal muscle (type I, MYH7, expressed in type 1 fibres; IIa, MYH2, expressed in 2A fibres; IIx, MYH1, expressed in 2B fibres) [20].
• While mutations in slow/beta cardiac MyHC (MYH7) are a common cause of familial hypertrophic cardiomyopathy, no skeletal myopathies have, until recently, been associated with mutations in MyHC [20].
• The patients carrying R663C, Q734P, E930K in MYH7 and R130C in TNNT2 expressed malignant phenotype [3].
• METHODS: Deoxyribonucleic (DNA) samples obtained from 389 HCM outpatients seen at this tertiary referral center were analyzed for mutations, using polymerase chain reaction, denaturing high-performance liquid chromatography, and DNA sequencing for all 38 protein-coding exons of MYH7 [4].
• The highest two-point LOD score was 26.05 at theta = 0.01 for MYH7 [21].

Analytical, diagnostic and therapeutic context of MYH7

• Varying disease profiles assessed using standard clinical, ECG and echocardiographic procedures in conjunction with mutation analysis led to the following conclusions: (1) In family MM the DeltaE927 deletion in MYH7 was assumed to be associated with complete penetrance [16].
• METHODS: The exons 3 to 26 of MYH7 were amplified by PCR, and the PCR products were sequenced in five non-kin HCM patients [18].
• The electrocardiogram is a more sensitive indicator than echocardiography of hypertrophic cardiomyopathy in families with a mutation in the MYH7 gene [22].
• As the myopathological findings in MDP1 show striking similarities to CPS, this porcine disorder may serve as an animal model for MPD1 [23].

References