Mutations in the slow skeletal muscle fiber myosin heavy chain gene (MYH7) cause laing early-onset distal myopathy (MPD1)

We previously linked Laing-type early-onset autosomal dominant distal myopathy (MPD1) to a 22-cM region of chromosome 14. One candidate gene in the region, MYH7, which is mutated in cardiomyopathy and myosin storage myopathy, codes for the myosin heavy chain of type I skeletal muscle fibers and cardiac ventricles. We have identified five novel heterozygous mutations--Arg1500Pro, Lys1617del, Ala1663Pro, Leu1706Pro, and Lys1729del in exons 32, 34, 35, and 36 of MYH7--in six families with early-onset distal myopathy. All five mutations are predicted, by in silico analysis, to locally disrupt the ability of the myosin tail to form the coiled coil, which is its normal structure. These findings demonstrate that heterozygous mutations toward the 3' end of MYH7 cause Laing-type early-onset distal myopathy. MYH7 is the fourth distal-myopathy gene to have been identified.     

Cardiomyopathy Mutations in the Tail of β-Cardiac Myosin Modify the Coiled-coil Structure and Affect Integration into Thick Filaments in Muscle Sarcomeres in Adult Cardiomyocytes

It is unclear why mutations in the filament-forming tail of myosin heavy chain (MHC) cause hypertrophic or dilated cardiomyopathy as these mutations should not directly affect contraction. To investigate this, we first investigated the impact of five hypertrophic cardiomyopathy-causing (N1327K, E1356K, R1382W, E1555K, and R1768K) and one dilated cardiomyopathy-causing (R1500W) tail mutations on their ability to incorporate into muscle sarcomeres in vivo. We used adenoviral delivery to express full-length wild type or mutant enhanced GFP-MHC in isolated adult cardiomyocytes. Three mutations (N1327K, E1356K, and E1555K) reduced enhanced GFP-MHC incorporation into muscle sarcomeres, whereas the remainder had no effect. No mutations significantly affected contraction. Fluorescence recovery after photobleaching showed that fluorescence recovery for the mutation that incorporated least well (N1327K) was significantly faster than that of WT with half-times of 25.1 ± 1.8 and 32.2 ± 2.5 min (mean ± S.E.), respectively. Next, we determined the effects of each mutation on the helical properties of wild type and seven mutant peptides (7, 11, or 15 heptads long) from the myosin tail by circular dichroism. R1382W and E1768K slightly increased the α-helical nature of peptides. The remaining mutations reduced α-helical content, with N1327K showing the greatest reduction. Only peptides containing residues 1301–1329 were highly α-helical suggesting that this region helps in initiation of coiled coil. These results suggest that small effects of mutations on helicity translate into a reduced ability to incorporate into sarcomeres, which may elicit compensatory hypertrophy.     

Actin nemaline myopathy mouse reproduces disease, suggests other actin disease phenotypes and provides cautionary note on muscle transgene expression

Mutations in the skeletal muscle α-actin gene (ACTA1) cause congenital myopathies including nemaline myopathy, actin aggregate myopathy and rod-core disease. The majority of patients with ACTA1 mutations have severe hypotonia and do not survive beyond the age of one. A transgenic mouse model was generated expressing an autosomal dominant mutant (D286G) of ACTA1 (identified in a severe nemaline myopathy patient) fused with EGFP. Nemaline bodies were observed in multiple skeletal muscles, with serial sections showing these correlated to aggregates of the mutant skeletal muscle α-actin-EGFP. Isolated extensor digitorum longus and soleus muscles were significantly weaker than wild-type (WT) muscle at 4 weeks of age, coinciding with the peak in structural lesions. These 4 week-old mice were ~30% less active on voluntary running wheels than WT mice. The α-actin-EGFP protein clearly demonstrated that the transgene was expressed equally in all myosin heavy chain (MHC) fibre types during the early postnatal period, but subsequently became largely confined to MHCIIB fibres. Ringbinden fibres, internal nuclei and myofibrillar myopathy pathologies, not typical features in nemaline myopathy or patients with ACTA1 mutations, were frequently observed. Ringbinden were found in fast fibre predominant muscles of adult mice and were exclusively MHCIIB-positive fibres. Thus, this mouse model presents a reliable model for the investigation of the pathobiology of nemaline body formation and muscle weakness and for evaluation of potential therapeutic interventions. The occurrence of core-like regions, internal nuclei and ringbinden will allow analysis of the mechanisms underlying these lesions. The occurrence of ringbinden and features of myofibrillar myopathy in this mouse model of ACTA1 disease suggests that patients with these pathologies and no genetic explanation should be screened for ACTA1 mutations.     

Dominant and recessive distal renal tubular acidosis mutations of kidney anion exchanger 1 induce distinct trafficking defects in MDCK cells

Distal renal tubular acidosis (dRTA), a kidney disease resulting in defective urinary acidification, can be caused by dominant or recessive mutations in the kidney Cl-/HCO3- anion exchanger (kAE1), a glycoprotein expressed in the basolateral membrane of alpha-intercalated cells. We compared the effect of two dominant (R589H and S613F) and two recessive (S773P and G701D) dRTA point mutations on kAE1 trafficking in Madin-Darby canine kidney (MDCK) epithelial cells. In contrast to wild-type (WT) kAE1 that was localized to the basolateral membrane, the dominant mutants (kAE1 R589H and S613F) were retained in the endoplasmic reticulum (ER) in MDCK cells, with a few cells showing in addition some apical localization. The recessive mutant kAE1 S773P, while misfolded and largely retained in the ER in non-polarized MDCK cells, was targeted to the basolateral membrane after polarization. The other recessive mutants, kAE1 G701D and designed G701E, G701R but not G701A or G701L mutants, were localized to the Golgi in both non-polarized and polarized cells. The results suggest that introduction of a polar mutation into a transmembrane segment resulted in Golgi retention of the recessive G701D mutant. When coexpressed, the dominant mutants retained kAE1 WT intracellularly, while the recessive mutants did not. Coexpression of recessive G701D and S773P mutants in polarized cells showed that these proteins could interact, yet no G701D mutant was detected at the basolateral membrane. Therefore, compound heterozygous patients expressing both recessive mutants (G701D/S773P) likely developed dRTA due to the lack of a functional kAE1 at the basolateral surface of alpha-intercalated cells.     

Functional effects of nemaline myopathy mutations on human skeletal alpha-actin

Mutations in human alpha-skeletal actin have been implicated in causing congenital nemaline myopathy, a disease characterized histopathologically by nemaline bodies in skeletal muscle and manifested in the patient as skeletal muscle weakness. Here we investigate the functional effects of three severe nemaline myopathy mutations (V43F, A138P, and R183G) in human alpha-skeletal actin. Wild-type and mutant actins were expressed and purified from the baculovirus/insect cell expression system. The mutations are located in different subdomains of actin; Val-43 is located in a flexible loop of subdomain 2, Ala-138 is near a hydrophobic cleft in the "hinge" region between subdomains 1 and 3, and Arg-183 is near the nucleotide-binding site. None of the three mutations affected the folding of the actin monomer, the velocity at which skeletal myosin moves actin in an in vitro motility assay, or the relative average isometric force supported by F-actin. Defects in fundamental actomyosin interactions are, therefore, unlikely to account for the muscle weakness observed in affected patients. There were, however, significant changes observed in the polymerization kinetics of V43F and A138P and in the rate of nucleotide release for V43F. No detectable defect was found for R183G. If these subtle changes in polymerization observed in vitro are amplified in the context of the sarcomere, it could in principle be one of the primary insults that triggers the development of nemaline myopathy.     

A1603P and K1617del,Mutations in β-Cardiac Myosin Heavy Chain that Cause Laing Early-Onset Distal Myopathy,Affect Secondary Structure and Filament Formation In Vitro and In Vivo

Over 20 mutations in β-cardiac myosin heavy chain (β-MHC), expressed in cardiac and slow muscle fibers, cause Laing early-onset distal myopathy (MPD-1), a skeletal muscle myopathy. Most of these mutations are in the coiled-coil tail and commonly involve a mutation to a proline or a single-residue deletion, both of which are predicted to strongly affect the secondary structure of the coiled coil. To test this, we characterized the effects of two MPD-1 causing mutations: A1603P and K1617del in vitro and in cells. Both mutations affected secondary structure, decreasing the helical content of 15 heptad and light meromyosin constructs. Both mutations also severely disrupted the ability of glutathione S-transferase–light meromyosin fusion proteins to form minifilaments in vitro, as demonstrated by negative stain electron microscopy. Mutant eGFP-tagged β-MHC accumulated abnormally into the M-line of sarcomeres in cultured skeletal muscle myotubes. Incorporation of eGFP-tagged β-MHC into sarcomeres in adult rat cardiomyocytes was reduced. Molecular dynamics simulations using a composite structure of part of the coiled coil demonstrated that both mutations affected the structure, with the mutation to proline (A1603P) having a smaller effect compared to K1617del. Taken together, it seems likely that the MPD-1 mutations destabilize the coiled coil, resulting in aberrant myosin packing in thick filaments in muscle sarcomeres, providing a potential mechanism for the disease.     

Phenotypic behavior of caveolin-3 R26Q,a mutant associated with hyperCKemia,distal myopathy,and rippling muscle disease

Four different phenotypes have been associated with CAV3 mutations: limb girdle muscular dystrophy-1C (LGMD-1C), rippling muscle disease (RMD), and distal myopathy (DM), as well as idiopathic and familial hyperCKemia (HCK). Detailed molecular characterization of two caveolin-3 mutations (P104L and TFT), associated with LGMD-1C, shows them to impart a dominant-negative effect on wild-type caveolin-3, rendering it dysfunctional through sequestration in the Golgi complex. Interestingly, substitution of glutamine for arginine at amino acid position 26 (R26Q) of caveolin-3 is associated not only with RMD but also with DM and HCK. However, the phenotypic behavior of the caveolin-3 R26Q mutation has never been evaluated in cultured cells. Thus we characterized the cellular and molecular properties of the R26Q mutant protein to better understand how this mutation can manifest as such distinct disease phenotypes. Here, we show that the caveolin-3 R26Q mutant is mostly retained at the level of the Golgi complex. The caveolin-3 R26Q mutant formed oligomers of a much larger size than wild-type caveolin-3 and was excluded from caveolae-enriched membranes. However, caveolin-3 R26Q did not behave in a dominant-negative fashion when coexpressed with wild-type caveolin-3. Thus the R26Q mutation behaves differently from other caveolin-3 mutations (P104L and TFT) that have been previously characterized. These data provide a possible explanation for the scope of the various disease phenotypes associated with the caveolin-3 R26Q mutation. We propose a haploinsufficiency model in which reduced levels of wild-type caveolin-3, although not rendered dysfunctional due to the caveolin-3 R26Q mutant protein, are insufficient for normal muscle cell function. muscle cell caveolae; caveolin-3; muscular dystrophy     

Myosin filament assembly requires a cluster of four positive residues located in the rod domain

Myosin has an intrinsic ability to organize into ordered thick filaments that mediate muscle contraction. Here, we use surface plasmon resonance and light scattering analysis to further characterize the molecular determinants that guide myosin filament assembly. Both assays identify a cluster of lysine and arginine residues as important for myosin polymerization in vitro. Moreover, in cardiomyocytes, replacement of these charged residues by alanine severely affects the incorporation of myosin into the distal ends of the sarcomere. Our findings show that a novel assembly element with a distinct charge profile is present at the C-terminus of sarcomeric myosins.

Structured summary of protein interactions

WT LMMbinds to WT LMM by surface plasmon resonance (View Interaction)WT LMMbinds to CT2 LMM by surface plasmon resonance (View Interaction)WT LMMbinds to Alanine mutant LMM by surface plasmon resonance (View Interaction)WT LMM and WT LMMbind by light scattering (View Interaction)Alanine mutant LMM and Alanine mutant LMMbind by light scattering (View Interaction)WT LMM and Alanine mutant LMMbind by light scattering (View Interaction)     

Two Novel Mutations in Myosin Binding Protein C Slow Causing Distal Arthrogryposis Type 2 in Two Large Han Chinese Families May Suggest Important Functional Role of Immunoglobulin Domain C2

Distal arthrogryposes (DAs) are a group of disorders that mainly involve the distal parts of the limbs and at least ten different DAs have been described to date. DAs are mostly described as autosomal dominant disorders with variable expressivity and incomplete penetrance, but recently autosomal recessive pattern was reported in distal arthrogryposis type 5D. Mutations in the contractile genes are found in about 50% of all DA patients. Of these genes, mutations in the gene encoding myosin binding protein C slow MYBPC1 were recently identified in two families with distal arthrogryposis type 1B. Here, we described two large Chinese families with autosomal dominant distal arthrogryposis type 2(DA2) with incomplete penetrance and variable expressivity. Some unique overextension contractures of the lower limbs and some distinctive facial features were present in our DA2 pedigrees. We performed follow-up DNA sequencing after linkage mapping and first identified two novel MYBPC1 mutations (c.1075G>A [p.E359K] and c.956C>T [p.P319L]) responsible for these Chinese DA2 families of which one introduced by germline mosacism. Each mutation was found to cosegregate with the DA2 phenotype in each family but not in population controls. Both substitutions occur within C2 immunoglobulin domain, which together with C1 and the M motif constitute the binding site for the S2 subfragment of myosin. Our results expand the phenotypic spectrum of MYBPC1-related arthrogryposis multiplex congenita (AMC). We also proposed the possible molecular mechanisms that may underlie the pathogenesis of DA2 myopathy associated with these two substitutions in MYBPC1.     

Palmitoylation-induced Aggregation of Cysteine-string Protein Mutants That Cause Neuronal Ceroid Lipofuscinosis

Recently, mutations in the DNAJC5 gene encoding cysteine-string protein α (CSPα) were identified to cause the neurodegenerative disorder adult-onset neuronal ceroid lipofuscinosis. The disease-causing mutations (L115R or ΔL116) occur within the cysteine-string domain, a region of the protein that is post-translationally modified by extensive palmitoylation. Here we demonstrate that L115R and ΔL116 mutant proteins are mistargeted in neuroendocrine cells and form SDS-resistant aggregates, concordant with the properties of other mutant proteins linked to neurodegenerative disorders. The mutant aggregates are membrane-associated and incorporate palmitate. Indeed, co-expression of palmitoyltransferase enzymes promoted the aggregation of the CSPα mutants, and chemical depalmitoylation solubilized the aggregates, demonstrating that aggregation is induced and maintained by palmitoylation. In agreement with these observations, SDS-resistant CSPα aggregates were present in brain samples from patients carrying the L115R mutation and were depleted by chemical depalmitoylation. In summary, this study identifies a novel interplay between genetic mutations and palmitoylation in driving aggregation of CSPα mutant proteins. We propose that this palmitoylation-induced aggregation of mutant CSPα proteins may underlie the development of adult-onset neuronal ceroid lipofuscinosis in affected families.     

Mutations in the N-terminal actin-binding domain of filamin C cause a distal myopathy

Linkage analysis of the dominant distal myopathy we previously identified in a large Australian family demonstrated one significant linkage region located on chromosome 7 and encompassing 18.6 Mbp and 151 genes. The strongest candidate gene was FLNC because filamin C, the encoded protein, is muscle-specific and associated with myofibrillar myopathy. Sequencing of FLNC cDNA identified a c.752T>C (p.Met251Thr) mutation in the N-terminal actin-binding domain (ABD); this mutation segregated with the disease and was absent in 200 controls. We identified an Italian family with the same phenotype and found a c.577G>A (p.Ala193Thr) filamin C ABD mutation that segregated with the disease. Filamin C ABD mutations have not been described, although filamin A and filamin B ABD mutations cause multiple musculoskeletal disorders. The distal myopathy phenotype and muscle pathology in the two families differ from myofibrillar myopathies caused by filamin C rod and dimerization domain mutations because of the distinct involvement of hand muscles and lack of pathological protein aggregation. Thus, like the position of FLNA and B mutations, the position of the FLNC mutation determines disease phenotype. The two filamin C ABD mutations increase actin-binding affinity in a manner similar to filamin A and filamin B ABD mutations. Cell-culture expression of the c.752T>C (p.Met251)Thr mutant filamin C ABD demonstrated reduced nuclear localization as did mutant filamin A and filamin B ABDs. Expression of both filamin C ABD mutants as full-length proteins induced increased aggregation of filamin. We conclude filamin C ABD mutations cause a recognizable distal myopathy, most likely through increased actin affinity, similar to the pathological mechanism of filamin A and filamin B ABD mutations.     

Impact of regulatory light chain mutation K104E on the ATPase and motor properties of cardiac myosin

Mutations in the cardiac myosin regulatory light chain (RLC, MYL2 gene) are known to cause inherited cardiomyopathies with variable phenotypes. In this study, we investigated the impact of a mutation in the RLC (K104E) that is associated with hypertrophic cardiomyopathy (HCM). Previously in a mouse model of K104E, older animals were found to develop cardiac hypertrophy, fibrosis, and diastolic dysfunction, suggesting a slow development of HCM. However, variable penetrance of the mutation in human populations suggests that the impact of K104E may be subtle. Therefore, we generated human cardiac myosin subfragment-1 (M2β-S1) and exchanged on either the wild type (WT) or K104E human ventricular RLC in order to assess the impact of the mutation on the mechanochemical properties of cardiac myosin. The maximum actin-activated ATPase activity and actin sliding velocities in the in vitro motility assay were similar in M2β-S1 WT and K104E, as were the detachment kinetic parameters, including the rate of ATP-induced dissociation and the ADP release rate constant. We also examined the mechanical performance of α-cardiac myosin extracted from transgenic (Tg) mice expressing human wild type RLC (Tg WT) or mutant RLC (Tg K104E). We found that α-cardiac myosin from Tg K104E animals demonstrated enhanced actin sliding velocities in the motility assay compared with its Tg WT counterpart. Furthermore, the degree of incorporation of the mutant RLC into α-cardiac myosin in the transgenic animals was significantly reduced compared with wild type. Therefore, we conclude that the impact of the K104E mutation depends on either the length or the isoform of the myosin heavy chain backbone and that the mutation may disrupt RLC interactions with the myosin lever arm domain.     

Myosin regulatory light chain mutation found in hypertrophic cardiomyopathy patients increases isometric force production in transgenic mice

FHC (familial hypertrophic cardiomyopathy) is a heritable form of cardiac hypertrophy caused by mutations in genes encoding sarcomeric proteins. The present study focuses on the A13T mutation in the human ventricular myosin RLC (regulatory light chain) that is associated with a rare FHC variant defined by mid-ventricular obstruction and septal hypertrophy. We generated heart-specific Tg (transgenic) mice with ~10% of human A13T-RLC mutant replacing the endogenous mouse cardiac RLC. Histopathological examinations of longitudinal heart sections from Tg-A13T mice showed enlarged interventricular septa and profound fibrotic lesions compared with Tg-WT (wild-type), expressing the human ventricular RLC, or non-Tg mice. Functional studies revealed an abnormal A13T mutation-induced increase in isometric force production, no change in the force-pCa relationship and a decreased Vmax of the acto-myosin ATPase. In addition, a fluorescence-based assay showed a 3-fold lower binding affinity of the recombinant A13T mutant for the RLC-depleted porcine myosin compared with WT-RLC. These results suggest that the A13T mutation triggers a hypertrophic response through changes in cardiac sarcomere organization and myosin cross-bridge function leading to abnormal remodelling of the heart. The significant functional changes observed, despite a low level of A13T mutant incorporation into myofilaments, suggest a 'poison-peptide' mechanism of disease.     

Deletion of the myopathy loop of Dictyostelium myosin II and its impact on motor functions

One of the putative actin-binding sites of Dictyostelium myosin II is the beta-strand-turn-beta-strand structure (Ile(398)-Leu-Ala-Gly-Arg-Asp(403)-Leu-Val(405)), the "myopathy loop, " which is located at the distal end of the upper 50-kDa subdomain and next to the conserved arginine (Arg(397)), whose mutation in human cardiac myosin results in familial hypertrophic cardiomyopathy. The myopathy loop contains the TEDS residue (Asp(403)), which is a target of the heavy-chain kinase in myosin I. Moreover, the loop contains a cluster of hydrophobic residues (Ile(398), Leu(399), Leu(404), and Val(405)), whose side chains are fully exposed to the solvent. In our study, the myopathy loop was deleted from Dictyostelium myosin II to investigate its functional roles. The mutation abolished hydrophobic interactions of actin and myosin in the strong binding state during the ATPase cycle. Association of the mutant myosin and actin was maintained only through ionic interactions under these conditions. Without strong hydrophobic interactions, the mutant myosin still exhibited motor functions, although at low levels. It is likely that the observed defects resulted mainly from a loss of the cluster of hydrophobic residues, since replacement of Asp(403) or Arg(402) with alanine generated a mutant with less severe or no defects compared with those of the deletion mutant.     

Point Mutations in Human β Cardiac Myosin Heavy Chain Have Differential Effects on Sarcomeric Structure and Assembly: An ATP Binding Site Change Disrupts Both Thick and Thin Filaments, Whereas Hypertrophic Cardiomyopathy Mutations Display Normal Assembly

Hypertrophic cardiomyopathy is a human heart disease characterized by increased ventricular mass, focal areas of fibrosis, myocyte, and myofibrillar disorganization. This genetically dominant disease can be caused by mutations in any one of several contractile proteins, including β cardiac myosin heavy chain (βMHC). To determine whether point mutations in human βMHC have direct effects on interfering with filament assembly and sarcomeric structure, full-length wild-type and mutant human βMHC cDNAs were cloned and expressed in primary cultures of neonatal rat ventricular cardiomyocytes (NRC) under conditions that promote myofibrillogenesis. A lysine to arginine change at amino acid 184 in the consensus ATP binding sequence of human βMHC resulted in abnormal subcellular localization and disrupted both thick and thin filament structure in transfected NRC. Diffuse βMHC K184R protein appeared to colocalize with actin throughout the myocyte, suggesting a tight interaction of these two proteins. Human βMHC with S472V mutation assembled normally into thick filaments and did not affect sarcomeric structure. Two mutant myosins previously described as causing human hypertrophic cardiomyopathy, R249Q and R403Q, were competent to assemble into thick filaments producing myofibrils with well defined I bands, A bands, and H zones. Coexpression and detection of wild-type βMHC and either R249Q or R403Q proteins in the same myocyte showed these proteins are equally able to assemble into the sarcomere and provided no discernible differences in subcellular localization. Thus, human βMHC R249Q and R403Q mutant proteins were readily incorporated into NRC sarcomeres and did not disrupt myofilament formation. This study indicates that the phenotype of myofibrillar disarray seen in HCM patients which harbor either of these two mutations may not be directly due to the failure of the mutant myosin heavy chain protein to assemble and form normal sarcomeres, but may rather be a secondary effect possibly resulting from the chronic stress of decreased βMHC function.     

Characterization of Two Second-Site Mutations Preventing Wild Type Protein Aggregation Caused by a Dominant Negative PMA1 Mutant

The correct biogenesis and localization of Pma1 at the plasma membrane is essential for yeast growth. A subset of PMA1 mutations behave as dominant negative because they produce aberrantly folded proteins that form protein aggregates, which in turn provoke the aggregation of the wild type protein. One approach to understand this dominant negative effect is to identify second-site mutations able to suppress the dominant lethal phenotype caused by those mutant alleles. We isolated and characterized two intragenic second-site suppressors of the PMA1-D378T dominant negative mutation. We present here the analysis of these new mutations that are located along the amino-terminal half of the protein and include a missense mutation, L151F, and an in-frame 12bp deletion that eliminates four residues from Cys409 to Ala412. The results show that the suppressor mutations disrupt the interaction between the mutant and wild type enzymes, and this enables the wild type Pma1 to reach the plasma membrane.     

A <Emphasis Type="Italic">de novo</Emphasis> germline mutation in <Emphasis Type="Italic">MYH7</Emphasis> causes a progressive dominant myopathy in pigs

Background

About 9% of the offspring of a clinically healthy Piétrain boar named ‘Campus’ showed a progressive postural tremor called Campus syndrome (CPS). Extensive backcross experiments suggested a dominant mode of inheritance, and the founder boar was believed to be a gonadal mosaic. A genome-scan mapped the disease-causing mutation to an 8 cM region of porcine chromosome 7 containing the MHY7 gene. Human distal myopathy type 1 (MPD1), a disease partially resembling CPS in pigs, has been associated with mutations in the MYH7 gene.

Results

The porcine MYH7 gene structure was predicted based on porcine reference genome sequence, porcine mRNA, and in comparison to the human ortholog. The gene structure was highly conserved with the exception of the first exon. Mutation analysis of a contiguous genomic interval of more than 22 kb spanning the complete MYH7 gene revealed an in-frame insertion within exon 30 of MYH7 (c.4320_4321insCCCGCC) which was perfectly associated with the disease phenotype and confirmed the dominant inheritance. The mutation is predicted to insert two amino acids (p.Ala1440_Ala1441insProAla) in a very highly conserved region of the myosin tail. The boar ‘Campus’ was shown to be a germline and somatic mosaic as assessed by the presence of the mutant allele in seven different organs.

Conclusion

This study illustrates the usefulness of recently established genomic resources in pigs. We have identified a spontaneous mutation in MYH7 as the causative mutation for CPS. This paper describes the first case of a disorder caused by a naturally occurring mutation in the MYH7 gene of a non-human mammalian species. Our study confirms the previous classification as a primary myopathy and provides a defined large animal model for human MPD1. We provide evidence that the CPS mutation occurred during the early development of the boar ‘Campus’. Therefore, this study provides an example of germline mosaicism with an asymptomatic founder.