Matrin-3 autosomal dominant myopathy, most commonly caused by a Ser85Cys (S85C) missense mutation, is a rare distal myopathy, presenting a heterogeneous phenotype. We report the clinical, physiological, radiological, and histological features of the first Portuguese patients diagnosed with p.Ser85Cys MATR3-related myopathy using a specific gene panel dedicated to "distal myopathies". Additionally, a narrative review of the literature was performed to contextualize our findings within the broader landscape of MATR3-related pathologies. Our case series describes the clinical findings of three patients diagnosed and followed in our center. The first patient was a 57-year-old male presenting with lower limb weakness, followed by loss of muscle force for fine motor gestures in the distal upper limb. Neurological examination revealed important muscle atrophy of the distal limbs and symmetrical motor deficit. The second patient, the brother of the aforementioned subject, was a 54-year-old male with similar symptoms associated with dysphagia and dysphonia. The third patient was a 58-year-old female, unrelated to the previous patients, presenting with distal weakness in the upper limbs and severe Achillean contractures. All three patients were investigated using needle electromyography and whole-body magnetic resonance imaging that disclosed a fatty infiltration pattern in the gastrocnemius, soleus, and tibialis anterior muscles. A muscle biopsy was performed solely for one patient and revealed rimmed vacuoles, consistent with previous reports. Genetic analysis found the same mutation in all three cases: c.254C>G, p.Ser85Cys in the MATR3 gene. The literature review included nine articles reporting families diagnosed with the p.Ser85Cys mutation in the MATR3 gene, and the main phenotypes associated with this genetic variant. Despite being a rare myopathy, with only a few cases reported, MATR3 gene mutations should be considered in patients with distal myopathy and rimmed vacuoles on muscle biopsy.

To determine the genetic cause of the disease in the previously reported family with adult-onset autosomal dominant distal myopathy (myopathy, distal, 3; MPD3). Continued clinical evaluation including muscle MRI and muscle pathology. A linkage analysis with single nucleotide polymorphism arrays and genome sequencing were used to identify the genetic defect, which was verified by Sanger sequencing. RNA sequencing was used to investigate the transcriptional effects of the identified genetic defect. Small hand muscles (intrinsic, thenar, and hypothenar) were first involved with spread to the lower legs and later proximal muscles. Dystrophic changes with rimmed vacuoles and cytoplasmic inclusions were observed in muscle biopsies at advanced stage. A single nucleotide polymorphism array confirmed the previous microsatellite-based linkage to 8p22-q11 and 12q13-q22. Genome sequencing of three affected family members combined with structural variant calling revealed a small heterozygous deletion of 160 base pairs spanning the second last exon 10 of the heterogeneous nuclear ribonucleoprotein A1 (HNRNPA1) gene, which is in the linked region on chromosome 12. Segregation of the mutation with the disease was confirmed by Sanger sequencing. RNA sequencing showed that the mutant allele produces a shorter mutant mRNA transcript compared with the wild-type allele. Immunofluorescence studies on muscle biopsies revealed small p62 and larger TDP-43 inclusions. A small exon 10 deletion in the gene HNRNPA1 was identified as the cause of MPD3 in this family. The new HNRNPA1-related phenotype, upper limb presenting distal myopathy, was thus confirmed, and the family displays the complexities of gene identification.

To clinically and pathologically characterize a cohort of patients presenting with a novel form of distal myopathy and to identify the genetic cause of this new muscular dystrophy. We studied 4 families (3 from Spain and 1 from Sweden) suffering from an autosomal dominant distal myopathy. Affected members showed adult onset asymmetric distal muscle weakness with initial involvement of ankle dorsiflexion later progressing also to proximal limb muscles. In all 3 Spanish families, we identified a unique missense variant in the ACTN2 gene cosegregating with the disease. The affected members of the Swedish family carry a different ACTN2 missense variant. ACTN2 encodes for alpha actinin2, which is highly expressed in the sarcomeric Z-disk with a major structural and functional role. Actininopathy is thus a new genetically determined distal myopathy. ANN NEUROL 2019;85:899-906.

Titin (TTN) is a large gene with 363 exons that encodes a large abundant protein (longest known polypeptide in nature) that is expressed in cardiac and skeletal muscles. TTN has an important role in the sarcomere organization, assembly of muscles, transmission of the force at the Z-line, passive myocyte stiffness, and resting tension maintenance in the I-band region. Mutation in extreme C terminus of TTN, situated at the end of M-band of the TTN in chromosome 2q31, results in tibial muscular dystrophy (TMD), also called Udd Distal Myopathy, which is an autosomal dominant distal myopathy. In this article, we report a novel mutation in TTN gene in a Saudi patient with bilateral facial weakness and scapular winging. This report adds to the literature a heterozygous missense variant c.85652C>G, p.(Pro28551Arg) in TTN gene, which may be related to genes that cause the disease, but more case validation is needed. The novel mutation described in the present study widened the genetic spectrum of TTN-associated diseases, which may benefit studies addressing this disease in the future.

In a previous report of a new phenotype with predominant scapulo-humeral-peroneal-distal myopathy associated with the Glu197Asp mutation in ACTA1, muscle biopsies did not show nemaline rods, nor could nemaline rods formation be demonstrated in an exhaustive functional in vivo or in vitro study. However, muscle biopsy in members of our family, carrying a similar clinical phenotype of some members of the original family and the same ACTA1 mutation, revealed the presence of numerous nemaline rods, suggesting that there must be other factors that explain the absence of nemaline rods.