CellLine: Human Mononuclear Myoblast

CellEFO: CL:0000056

GeneFunction: GO:0007015 (Actin Filament Organization)

GeneAlteration: A wild-type C-terminal EGFP-tagged β-TM fusion gene was generated by amplifying TPM2 and cloning it into a vector while introducing XhoI and EcoRI restriction sites. All mutant constructs were formed by site-directed mutagenesis and cloning into E. coli. These constructs were sequenced to verify the correct coding sequence and introduction of the mutations. They were then introduced to human myoblast cells and mouse C2C12 cells via transfection.

FunctionalEvidence: The expression of these TPM2 mutants in cultured cells demonstrated several morphological abnormalities reminiscent of those seen in nemaline myopathy patients. In the human myoblasts/differentiated cells, these included various types of aggregates including nuclear, cytoplasmic, endogenous, and perinuclear. Large accumulations of actin along with clouds around the nucleus and cytoplasm with unorganized structure were also present. Poor incorporation of stress fibers, what appeared to be disorganized sarcomeric structure, and rod-like structures both intranuclear and in the myotubes in particular all demonstrate clear similarities to those phenotypes seen in nemaline myopathy, namely the presence of nemaline rods, disorganized sarcomeres, and z-disc abnormalities. These two groups of pathologies also seem to share the same mechanism, specifically the TPM2 mutations destabilizing the actin-myosin structures and causing accumulation and abnormal structures to form. Similarly, the modified C2C12 myoblasts/myotubes also displayed peripheral and perinuclear aggregates in both stages of development as well as diffuse cytoplasmic labeling of stress fibers. They had difficulty differentiating, as they appeared to be fused rather than elongated and multinucleated. This further supports the connection between the gene disruption and the pathologies that are demonstrated here.

CellVariant1: NM_003289.3:c.121G>A (p.Glu41Lys)

ClinVar: 12464 http://www.ncbi.nlm.nih.gov/clinvar/variation/12464

CellVariant2: NM_003289.3:c.142_144delAAG (p.Lys49del)

ClinVar: 12466 https://www.ncbi.nlm.nih.gov/clinvar/variation/12466/

CellVariant3: NM_003289.3:c.154_156dup (p.Gly52dup)

ClinVar: 140485 https://www.ncbi.nlm.nih.gov/clinvar/variation/140485/

CellVariant4: NM_003289.3:c.364G>A (p.Glu122Lys)

CAID: CA373367963 http://reg.genome.network/redmine/projects/registry/genboree_registry/by_caid?caid=CA373367963

CellVariant5: NM_003289.3:c.606C>G (p.Asn202Lys)

ClinVar: 12467 https://www.ncbi.nlm.nih.gov/clinvar/variation/12467/

CellLine: Human Mononuclear Myoblast

CellEFO: CL:0000056

GeneFunction: GO:0007015 (Actin Filament Organization)

GeneAlteration: A wild-type C-terminal EGFP-tagged β-TM fusion gene was generated by amplifying TPM2 and cloning it into a vector while introducing XhoI and EcoRI restriction sites. All mutant constructs were formed by site-directed mutagenesis and cloning into E. coli. These constructs were sequenced to verify the correct coding sequence and introduction of the mutations. They were then introduced to human myoblast cells and mouse C2C12 cells via transfection.

FunctionalEvidence: The expression of these TPM2 mutants in cultured cells demonstrated several morphological abnormalities reminiscent of those seen in nemaline myopathy patients. In the human myoblasts/differentiated cells, these included various types of aggregates including nuclear, cytoplasmic, endogenous, and perinuclear. Large accumulations of actin along with clouds around the nucleus and cytoplasm with unorganized structure were also present. Poor incorporation of stress fibers, what appeared to be disorganized sarcomeric structure, and rod-like structures both intranuclear and in the myotubes in particular all demonstrate clear similarities to those phenotypes seen in nemaline myopathy, namely the presence of nemaline rods, disorganized sarcomeres, and z-disc abnormalities. These two groups of pathologies also seem to share the same mechanism, specifically the TPM2 mutations destabilizing the actin-myosin structures and causing accumulation and abnormal structures to form. Similarly, the modified C2C12 myoblasts/myotubes also displayed peripheral and perinuclear aggregates in both stages of development as well as diffuse cytoplasmic labeling of stress fibers. They had difficulty differentiating, as they appeared to be fused rather than elongated and multinucleated. This further supports the connection between the gene disruption and the pathologies that are demonstrated here.

CellVariant1: NM_003289.3:c.121G>A (p.Glu41Lys)

ClinVar: 12464 http://www.ncbi.nlm.nih.gov/clinvar/variation/12464

CellVariant2: NM_003289.3:c.142_144delAAG (p.Lys49del)

ClinVar: 12466 https://www.ncbi.nlm.nih.gov/clinvar/variation/12466/

CellVariant3: NM_003289.3:c.154_156dup (p.Gly52dup)

ClinVar: 140485 https://www.ncbi.nlm.nih.gov/clinvar/variation/140485/

CellVariant4: NM_003289.3:c.364G>A (p.Glu122Lys)

CAID: CA373367963 http://reg.genome.network/redmine/projects/registry/genboree_registry/by_caid?caid=CA373367963

CellVariant5: NM_003289.3:c.606C>G (p.Asn202Lys)

ClinVar: 12467 https://www.ncbi.nlm.nih.gov/clinvar/variation/12467/

Case1: Female, 12 yrs onset, Dutch

CasePresentingHPOs: HP:0002093, HP:0001288, HP:0003690, HP:0010628, HP:0003722, HP:0003202, HP:0003798 (Respiratory insufficiency, Gait difficulties, Limb muscle weakness, Facial muscle weakness, Neck flexor weakness, Muscle hypotrophy, Nemaline rods)

HPOsFreeText: Mild form of nemaline myopathy, Wheelchair from the age of 48, Selective hypotrophy of Type 1 muscle fibres

CaseNotHPOs: N/A

NotHPOsFreeText: N/A

CaseAddInfo: No family history of neuromuscular disorders, Variant was not detected in healthy mother or 7 unaffected siblings, Father was deceased so no sample was available

CasePreviousTesting: N/A

CaseGenotypingMethod: Genomic DNA and RNA was extracted from blood or lymphoblastoid cell lines. SSCP was used to analyze all 10 exons of TPM2. After locating the mutations, RT-PCR was used to confirm the mutated allele expression and haplotype analysis was performed on the probands and their family.

Variant: NM_003289.3:c.440A>C (p.Gln147Pro)

ClinVar: 12461 https://www.ncbi.nlm.nih.gov/clinvar/variation/12461/

gnomAD: Not in gnomAD

Case1: Female, 12 yrs onset, Dutch

CasePresentingHPOs: HP:0002093, HP:0001288, HP:0003690, HP:0010628, HP:0003722, HP:0003202, HP:0003798 (Respiratory insufficiency, Gait difficulties, Limb muscle weakness, Facial muscle weakness, Neck flexor weakness, Muscle hypotrophy, Nemaline rods)

HPOsFreeText: Mild form of nemaline myopathy, Wheelchair from the age of 48, Selective hypotrophy of Type 1 muscle fibres

CaseNotHPOs: N/A

NotHPOsFreeText: N/A

CaseAddInfo: No family history of neuromuscular disorders, Variant was not detected in healthy mother or 7 unaffected siblings, Father was deceased so no sample was available

CasePreviousTesting: N/A

CaseGenotypingMethod: Genomic DNA and RNA was extracted from blood or lymphoblastoid cell lines. SSCP was used to analyze all 10 exons of TPM2. After locating the mutations, RT-PCR was used to confirm the mutated allele expression and haplotype analysis was performed on the probands and their family.

Variant: NM_003289.3:c.440A>C (p.Gln147Pro)

ClinVar: 12461 https://www.ncbi.nlm.nih.gov/clinvar/variation/12461/

gnomAD: Not in gnomAD