Magnetic Resonance Imaging characteristics in case of TOR1AIP1 muscular dystrophy

Miyoshi myopathy associated with spine rigidity and multiple contractures: a case report

BACKGROUND

Dysferlinopathy is a phenotypically heterogeneous group of hereditary diseases caused by mutations in the DYSF gene. Early contractures are considered rare, and rigid spine syndrome in dysferlinopathy has been previously reported only once.

CASE PRESENTATION

We describe a 23-year-old patient with Miyoshi myopathy with a rigid spine and multiple contractures, a rare phenotypic variant. The disease first manifested when the patient was 13 years old, with fatigue of the gastrocnemius muscles and the development of pronounced contractures of the Achilles tendons, flexors of the fingers, and extensors of the toes, followed by the involvement of large joints and the spine. Magnetic resonance imaging revealed signs of connective tissue and fatty replacement of the posterior muscles of the thighs and lower legs. Edema was noted in the anterior and medial muscle groups of the thighs, lower legs, and the multifidus muscle of the back. Whole genome sequencing revealed previously described mutations in the DYSF gene in exon 39 (c.4282 C > T) and intron 51 (c.5785-824 C > T). An immunohistochemical analysis and Western blot showed the complete absence of dysferlin protein expression in the muscle fibers.

CONCLUSIONS

This case expands the range of clinical and phenotypic correlations of dysferlinopathy and complements the diagnostic search for spine rigidity.

TOR1AIP1-Associated Nuclear Envelopathies

Human TOR1AIP1 encodes LAP1, a nuclear envelope protein expressed in most human tissues, which has been linked to various biological processes and human diseases. The clinical spectrum of diseases related to mutations in TOR1AIP1 is broad, including muscular dystrophy, congenital myasthenic syndrome, cardiomyopathy, and multisystemic disease with or without progeroid features. Although rare, these recessively inherited disorders often lead to early death or considerable functional impairment. Developing a better understanding of the roles of LAP1 and mutant TOR1AIP1-associated phenotypes is paramount to allow therapeutic development. To facilitate further studies, this review provides an overview of the known interactions of LAP1 and summarizes the evidence for the function of this protein in human health. We then review the mutations in the TOR1AIP1 gene and the clinical and pathological characteristics of subjects with these mutations. Lastly, we discuss challenges to be addressed in the future.

Selective loss of a LAP1 isoform causes a muscle-specific nuclear envelopathy

The nuclear envelope (NE) separates the nucleus from the cytoplasm in all eukaryotic cells. A disruption of the NE structure compromises normal gene regulation and leads to severe human disorders collectively classified as nuclear envelopathies and affecting skeletal muscle, heart, brain, skin, and bones. The ubiquitous NE component LAP1B is encoded by TOR1AIP1, and the use of an alternative start codon gives rise to the shorter LAP1C isoform. TOR1AIP1 mutations have been identified in patients with diverging clinical presentations such as muscular dystrophy, progressive dystonia with cerebellar atrophy, and a severe multi-systemic disorder, but the correlation between the mutational effect and the clinical spectrum remains to be determined. Here, we describe a novel TOR1AIP1 patient manifesting childhood-onset muscle weakness and contractures, and we provide clinical, histological, ultrastructural, and genetic data. We demonstrate that the identified TOR1AIP1 frameshift mutation leads to the selective loss of the LAP1B isoform, while the expression of LAP1C was preserved. Through comparative review of all previously reported TOR1AIP1 cases, we delineate a genotype/phenotype correlation and conclude that LAP1B-specific mutations cause a progressive skeletal muscle phenotype, while mutations involving a loss of both LAP1B and LAP1C isoforms induce a syndromic disorder affecting skeletal muscle, brain, eyes, ear, skin, and bones.

Muscular involvement and tendon contracture in limb-girdle muscular dystrophy 2Y: a mild adult phenotype and literature review

Background

Limb girdle muscular dystrophy type 2Y (LGMD2Y) is a rare subgroup of limb girdle muscular dystrophy featuring limb-girdle weakness, tendon contracture and cardiac involvement. It is caused by the mutation of TOR1AIP1, which encodes nuclear membrane protein LAP1 (lamina-associated polypeptide 1) and comprises heterogeneous phenotypes. The present study reported a patient with a novel homozygous TOR1AIP1 mutation that presented with selective muscle weakness, which further expanded the phenotype of LGMD2Y- and TOR1AIP1-associated nuclear envelopathies.

Case presentation

A 40-year-old male presented with Achilles tendon contracture and muscle weakness that bothered him from 8 years old. While the strength of his distal and proximal upper limbs was severely impaired, the function of his lower limbs was relatively spared. Muscle pathology showed dystrophic features, and electron microscopy showed ultrastructural abnormalities of disrupted muscle nuclei envelopes. Whole-exome sequencing showed a frameshift mutation in TOR1AIP1 (c.98dupC).

Conclusion

We reported a novel mild phenotype of LGMD2Y with relatively selective distal upper limb weakness and joint contracture and revealed the heterogeneity of LGDM2Y and the role of the LAP1 isoform by literature review.

Nuclear Accumulation of LAP1:TRF2 Complex during DNA Damage Response Uncovers a Novel Role for LAP1

Lamina-associated polypeptide 1 (LAP1) is a nuclear envelope (NE) protein whose function remains poorly characterized. In a recent LAP1 protein interactome study, a putative regulatory role in the DNA damage response (DDR) has emerged and telomeric repeat-binding factor 2 (TRF2), a protein intimately associated with this signaling pathway, was among the list of LAP1 interactors. To gain insights into LAP1's physiological properties, the interaction with TRF2 in human cells exposed to DNA-damaging agents was investigated. The direct LAP1:TRF2 binding was validated in vitro by blot overlay and in vivo by co-immunoprecipitation after hydrogen peroxide and bleomycin treatments. The regulation of this protein interaction by LAP1 phosphorylation was demonstrated by co-immunoprecipitation and mass spectrometry following okadaic acid exposure. The involvement of LAP1 and TRF2 in the DDR was confirmed by their increased nuclear protein levels after bleomycin treatment, evaluated by immunoblotting, as well as by their co-localization with DDR factors at the NE and within the nucleoplasm, assessed by immunocytochemistry. Effectively, we showed that the LAP1:TRF2 complex is established during a cellular response against DNA damage. This work proposes a novel functional role for LAP1 in the DDR, revealing a potential biological mechanism that may be disrupted in LAP1-associated pathologies.