Exon skipping caused by splicing mutation in TNNT1 nemaline myopathy

A homozygous single-nucleotide variant in TNNT1 causes abnormal troponin T isoform expression in a patient with severe nemaline myopathy: A case report

BACKGROUND

Slow skeletal troponin T (ssTnT, TNNT1) is the tropomyosin-binding subunit of the troponin complex in the slow-twitch fibers of skeletal muscle. Exon 5 of TNNT1 is alternatively spliced, and retention of the 3' region of intron 11 (exon 12') has also been described. Variants in TNNT1 are known to cause nemaline myopathy (NM).

OBJECTIVE

To identify and further investigate the disease-causing variant in a patient with lethal NM.

METHODS

The genetic analyses included a gene panel, Sanger sequencing, whole-exome sequencing, and targeted array-CGH. Muscle biopsy was analyzed using routine histopathological methods. The alternative splicing of TNNT1 exon 12 in patient muscle was quantified from RNA sequencing data, and the protein expression was confirmed by western blot. Expression of ssTnT in patient muscle was studied by immunohistology.

RESULTS

The patient presented with arthrogryposis, stiffness, respiratory insufficiency, and minimal spontaneous movements. Histopathology showed hypotrophy and predominance of type II fibers, perimysial connective tissue accumulation, and nemaline bodies. The patient was homozygous for the TNNT1 missense variant (NM_003283.6:c.653C > G, p.(Pro218Arg), NM_ 001126132.3:c.612-7C > G), predicted to disrupt splicing. RNA-seq revealed inclusion of exon 12' in 49.85% of transcripts, whereas in controls exon 12' was not expressed. Exon 12' expression on the protein level was confirmed by western blot. Immunohistology showed strong ssTnT expression in remaining type I fibers, and low expression in type IIA fibers.

CONCLUSIONS

The c.653C > G variant was shown to alter TNNT1 splicing. The results suggest a novel pathogenetic mechanism involving abnormal expression of a troponin T isoform.

Expression patterns of housekeeping genes and tissue-specific genes in black goats across multiple tissues

Black goats are a significant meat breed in southern China. To investigate the expression patterns and biological functions of genes in various tissues of black goats, we analyzed housekeeping genes (HKGs), tissue-specific genes (TSGs), and hub genes (HUBGs) across 23 tissues. Additionally, we analyzed HKGs in 13 tissues under different feeding conditions. We identified 2968 HKGs, including six important ones. Interestingly, HKGs in grazing black goats demonstrated higher and more stable expression levels. We discovered a total of 9912 TSGs, including 134 newly identified ones. The number of TSGs for mRNA and lncRNA were nearly equal, with 127 mRNA TSGs expressed solely in one tissue. Additionally, the predicted functions of tissue-specific long non-coding RNAs (lncRNAs) targeting mRNAs corresponded with the physiological functions of the tissues.Weighted gene co-expression network analysis (WGCNA) constructed 30 modules, where the dark grey module consists almost entirely of HKGs, and TSGs are located in modules most correlated with their respective tissues. Additionally, we identified 289 HUBGs, which are involved in regulating the physiological functions of their respective tissues. Overall, these identified HKGs, TSGs, and HUBGs provide a foundation for studying the molecular mechanisms affecting the genetic and biological processes of complex traits in black goats.

A rare TNNT1 gene variant causing creatine kinase elevation in nemaline myopathy: c.271_273del (p.Lys91del)

BACKGROUND

Nemaline Myopathy (NM) is a rare genetic disorder that affects muscle function and is characterized by the presence of nemaline rods in muscle fibers. These rods are abnormal structures that interfere with muscle contraction and can cause muscle weakness, respiratory distress, and other complications. NM is caused by variants in several genes, including TNNT1, which encodes the protein troponin T1. NM is inherited in an autosomal recessive pattern. The prevalence of heterozygous TNNT1 variants has been reported to be 1/152,000, indicating that the disease is relatively rare.

OBJECTIVE

Investigation of TNNT1 gene variants that may cause cretin kinase elevation.

METHODS

Detailed family histories and clinical data were recorded. Whole exome sequencing was performed and family segregation was done by Sanger sequencing.

RESULTS

In this study, we report a 5-year-old girl with a novel variant recessive congenital TNNT1 myopathy. The patient had a novel homozygous (c.271_273del) deletion in the TNNT1 gene that is associated with creatine kinase elevation, which is a marker of muscle damage.

CONCLUSION

This case expands the phenotypic spectrum of TNNT1 myopathy and highlights the importance of genetic testing and counseling for families affected by this rare disorder. In this study provides valuable insights into the genetic basis of NM and highlights the importance of early diagnosis and management for patients with this rare disorder. Further research is needed to better understand the pathophysiology of TNNT1 myopathy and to develop effective treatments for this debilitating condition.