Exon skipping in Duchenne Muscle dystrophy due to a silent p.Ser443= mutation in the DMD gene

Does β-Hydroxy-β-Methylbutyrate Have Any Potential to Support the Treatment of Duchenne Muscular Dystrophy in Humans and Animals?

Skeletal muscle is the protein reservoir of our body and an important regulator of glucose and lipid homeostasis. The dystrophin gene is the largest gene and has a key role in skeletal muscle construction and function. Mutations in the dystrophin gene cause Duchenne and Becker muscular dystrophy in humans, mice, dogs, and cats. Duchenne muscular dystrophy (DMD) is an X-linked neuromuscular condition causing progressive muscle weakness and premature death. β-hydroxy β-methylbutyrate (HMB) prevents deleterious muscle responses under pathological conditions, including tumor and chronic steroid therapy-related muscle losses. The use of HMB as a dietary supplement allows for increasing lean weight gain; has a positive immunostimulatory effect; is associated with decreased mortality; and attenuates sarcopenia in elderly animals and individuals. This study aimed to identify some genes, metabolic pathways, and biological processes which are common for DMD and HMB based on existing literature and then discuss the consequences of that interaction.

Identification of a novel TNNI3 synonymous variant causing intron retention in autosomal recessive dilated cardiomyopathy

BACKGROUND

Dilated cardiomyopathy type 2A (DCM2A, MIM: #611880) is a rare autosomal recessive heart disease leading to heart failure and sudden cardiac death. However, the causative role of TNNI3 in DCM2A is still questioned due to few cases reported and the conflicting molecular biological evidence.

METHODS

Trio whole-exome sequencing (trio-WES) was performed in a Chinese family with dilated cardiomyopathy. Sanger sequencing and real-time quantitative PCR were used to confirm the variants identified. Expression outcome caused by the synonymous mutation was validated by minigene splicing analyses.

RESULTS

The one-year-old girl presented severe left ventricular enlargement and significantly reduced left ventricular systolic function and she died of respiratory and heart failure soon after her diagnosis. Trio-WES revealed a compound heterozygous variants of TNNI3, a novel c.24G＞A (p.Ala8Ala) (NM_000363.4) in exon 2 and a deletion of entire gene. Minigene splicing analyses showed it led to an intron retention (c.24 + 1_24 + 45ins) by intron 2 cryptic splicing.

CONCLUSIONS

Our study describes and characterizes a synonymous mutation in TNNI3 gene, supporting the clinical diagnosis of an autosomal recessive DCM. Our study emphasizes the importance of functional analysis to assess the potential pathogenicity of synonymous mutations, especially when the synonymous variants are not annotated as benign.

Code inside the codon: The role of synonymous mutations in regulating splicing machinery and its impact on disease

In eukaryotes, precise pre-mRNA processing, including alternative splicing, is essential to carry out the intricate protein translation process. Both point mutations (that alter the translated protein sequence) and synonymous mutations (that do not alter the translated protein sequence) are capable of affecting the splicing process. Synonymous mutations are known to affect gene expression via altering mRNA stability, mRNA secondary structure, splicing processes, and translational kinetics. In higher eukaryotes, precise splicing is regulated by three weakly conserved cis-elements, 5' and 3' splice sites and the branch site. Many other cis-acting elements (exonic/intronic splicing enhancers and silencers) and trans-acting splicing factors (serine and arginine-rich proteins and heterogeneous nuclear ribonucleoproteins) have also been found to enhance or suppress the splicing process. The appearance of synonymous mutations in cis-acting elements can alter the splicing process by changing the binding pattern of splicing factors to exonic splicing enhancers or silencer motifs. This results in exon skipping, intron retention, and various other forms of alternative splicing, eventually leading to the emergence of a wide range of diseases. The focus of this review is to elucidate the role of synonymous mutations and their impact on abnormal splicing mechanisms. Further, this study highlights the function of synonymous mutation in mediating abnormal splicing in cancer and development of X-linked, and autosomal inherited diseases.