Nemaline Myopathy in Brazilian Patients: Molecular and Clinical Characterization.

Nemaline myopathy (NM), a structural congenital myopathy, presents a significant clinical and genetic heterogeneity. Here, we compiled molecular and clinical data of 30 Brazilian patients from 25 unrelated families. Next-generation sequencing was able to genetically classify all patients: sixteen families (64%) with mutation in NEB, five (20%) in ACTA1, two (8%) in KLHL40, and one in TPM2 (4%) and TPM3 (4%). In the NEB-related families, 25 different variants, 11 of them novel, were identified; splice site (10/25) and frame shift (9/25) mutations were the most common. Mutation c.24579 G>C was recurrent in three unrelated patients from the same region, suggesting a common ancestor. Clinically, the "typical" form was the more frequent and caused by mutations in the different NM genes. Phenotypic heterogeneity was observed among patients with mutations in the same gene. Respiratory involvement was very common and often out of proportion with limb weakness. Muscle MRI patterns showed variability within the forms and genes, which was related to the severity of the weakness. Considering the high frequency of NEB mutations and the complexity of this gene, NGS tools should be combined with CNV identification, especially in patients with a likely non-identified second mutation.

Concordant utrophin upregulation in phenotypically discordant DMD/BMD brothers.

Utrophin expression was investigated in two phenotypically discordant Duchenne muscular dystrophy half-brothers. The youngest was wheelchair-bound at age 9, while his mildly affected older brother was able to walk without difficulties at age 15. DNA analysis revealed an out-of-frame exon 2 duplication in the DMD gene, associated with muscle dystrophin protein deficiency. Utrophin localization and quantity was analyzed and compared in both sibs to verify whether this could explain the milder phenotype of the older brother. Immunofluorescence analysis showed a clear sarcolemmal labeling for utrophin in both of them, which was present in regenerating as well as in mature fibers. On western blot analysis, utrophin amount was increased 3.4 and 3.3 fold respectively, as compared to normal controls, while it was increased 1.7 to 4.0 fold in a group of DMD patients within the typical range of clinical progression. These data are in accordance with our previous observations suggesting no correlation between phenotype severity and utrophin up-regulation or sarcolemmal localization in dystrophinopathies. Finding the protective mechanisms in patients with milder course is of utmost interest to direct therapeutic targets.

Assessing pathogenicity for novel mutation/sequence variants: the value of healthy older individuals.

Improvement in DNA technology is increasingly revealing unexpected/unknown mutations in healthy persons and generating anxiety due to their still unknown health consequences. We report a 44-year-old healthy father of a 10-year-old daughter with bilateral coloboma and hearing loss, but without muscle weakness, in whom a whole-genome CGH revealed a deletion of exons 38-44 in the dystrophin gene. This mutation was inherited from her asymptomatic father, who was further clinically and molecularly evaluated for prognosis and genetic counseling (GC). This deletion was never identified by us in 982 Duchenne/Becker patients. To assess whether the present case represents a rare case of non-penetrance, and aiming to obtain more information for prognosis and GC, we suggested that healthy older relatives submit their DNA for analysis, to which several complied. Mutation analysis revealed that his mother, brother, and 56-year-old maternal uncle also carry the 38-44 deletion, suggesting it an unlikely cause of muscle weakness. Genome sequencing will disclose mutations and variants whose health impact are still unknown, raising important problems in interpreting results, defining prognosis, and discussing GC. We suggest that, in addition to family history, keeping the DNA of older relatives could be very informative, in particular for those interested in having their genome sequenced.