Mitochondria are dynamic organelles ubiquitously present in nucleated eukaryotic cells, subserving multiple metabolic functions, including cellular ATP generation by oxidative phosphorylation (OXPHOS). The OXPHOS machinery comprises five transmembrane respiratory chain enzyme complexes (RC). Defective OXPHOS gives rise to mitochondrial diseases (mtD). The incredible phenotypic and genetic diversity of mtD can be attributed at least in part to the RC dual genetic control (nuclear DNA (nDNA) and mitochondrial DNA (mtDNA)) and the complex interaction between the two genomes. Despite the increasing use of next-generation-sequencing (NGS) and various omics platforms in unravelling novel mtD genes and pathomechanisms, current clinical practice for investigating mtD essentially involves a multipronged approach including clinical assessment, metabolic screening, imaging, pathological, biochemical and functional testing to guide molecular genetic analysis. This review addresses the broad muscle pathology landscape including genotype–phenotype correlations in adult and paediatric mtD, the role of immunodiagnostics in understanding some of the pathomechanisms underpinning the canonical features of mtD, and recent diagnostic advances in the field.

Background: Integrin α7β1 is a major laminin receptor in skeletal and cardiac muscle. In skeletal muscle, integrin α7β1 plays an important role during muscle development and has been described as an important modifier of skeletal muscle diseases. The integrin α7β1 is also highly expressed in the heart, but its precise role in cardiac function is unknown. Mutations in the integrin α7 gene ( ITGA7 ) have been reported in children with congenital myopathy. Methods and Results: In this study, we described skeletal and cardiac muscle pathology in Itga7 ^−/− mice and 5 patients from 2 unrelated families with ITGA7 mutations. Proband in family 1 presented a homozygous c.806_818del [p.S269fs] variant, and proband in family 2 was identified with 2 intron variants in the ITGA7 gene. The complete absence of the integrin α7 protein in muscle supports the ITGA7 mutations are pathogenic. We performed electrocardiography, echocardiography, or cardiac magnetic resonance imaging, and histological biopsy analyses in patients with ITGA7 deficiency and Itga7 ^−/− mice. The patients exhibited cardiac dysrhythmia and dysfunction from the third decade of life and late‐onset respiratory insufficiency, but with relatively mild limb muscle involvement. Mice demonstrated corresponding abnormalities in cardiac conduction and contraction as well as diaphragm muscle fibrosis. Conclusions: Our data suggest that loss of integrin α7 causes a novel form of adult‐onset cardiac dysfunction indicating a critical role for the integrin α7β1 in normal cardiac function and highlights the need for long‐term cardiac monitoring in patients with ITGA7 ‐related congenital myopathy.

Aims: TRAPPC11, a subunit of the transport protein particle (TRAPP) complex, is important for complex integrity and anterograde membrane transport from the endoplasmic reticulum (ER) to the ER–Golgi intermediate compartment. Several individuals with TRAPPC11 mutations have been reported with muscle weakness and other features including brain, liver, skeletal and eye involvement. A detailed analysis of brain and muscle pathology will further our understanding of the presentation and aetiology of TRAPPC11 disease.Methods: We describe five cases of early‐onset TRAPPC11‐related muscular dystrophy with a systematic review of muscle pathology in all five individuals, post‐mortem brain pathology findings in one and membrane trafficking assays in another.Results: All affected individuals presented in infancy with muscle weakness, motor delay and elevated serum creatine kinase (CK). Additional features included cataracts, liver disease, intellectual disability, cardiomyopathy, movement disorder and structural brain abnormalities. Muscle pathology in all five revealed dystrophic changes, universal hypoglycosylation of alpha‐dystroglycan and variably reduced dystrophin‐associated complex proteins. Membrane trafficking assays showed defective Golgi trafficking in one individual. Neuropathological examination of one individual revealed cerebellar atrophy, granule cell hypoplasia, Purkinje cell (PC) loss, degeneration and dendrite dystrophy, reduced alpha‐dystroglycan (IIH6) expression in PC and dentate neurones and absence of neuronal migration defects.Conclusions: This report suggests that recessive mutations in TRAPPC11 are linked to muscular dystrophies with hypoglycosylation of alpha‐dystroglycan. The structural cerebellar involvement that we document for the first time resembles the neuropathology reported in N‐linked congenital disorders of glycosylation (CDG) such as PMM2‐CDG, suggesting defects in multiple glycosylation pathways in this condition.