Biallelic variants in SNUPN cause a limb girdle muscular dystrophy with myofibrillar-like features

Alterations in RNA-splicing are a molecular hallmark of several neurological diseases, including muscular dystrophies where mutations in genes involved in RNA metabolism or characterised by alterations in RNA splicing have been described. Here, we present five patients from two unrelated families with a limb-girdle muscular dystrophy (LGMD) phenotype carrying a biallelic variant in SNUPN gene. Snurportin-1, the protein encoded by SNUPN, plays an important role in the nuclear transport of small nuclear ribonucleoproteins (snRNPs), essential components of the spliceosome. We combine deep phenotyping, including clinical features, histopathology and muscle magnetic resonance image (MRI), with functional studies in patient-derived cells and muscle biopsies to demonstrate that variants in SNUPN are the cause of a new type of LGMD according to current definition. Moreover, an in vivo model in Drosophila melanogaster further supports the relevance of Snurportin-1 in muscle. SNUPN patients show a similar phenotype characterised by proximal weakness starting in childhood, restrictive respiratory dysfunction and prominent contractures, although interindividual variability in terms of severity even in individuals from the same family was found. Muscle biopsy showed myofibrillar-like features consisting of myotilin deposits and Z-disc disorganisation. MRI showed predominant impairment of paravertebral, vasti, sartorius, gracilis, peroneal and medial gastrocnemius muscles. Conservation and structural analyses of Snurportin-1 p.Ile309Ser variant suggest an effect in nuclear-cytosol snRNP trafficking. In patient-derived fibroblasts and muscle, cytoplasmic accumulation of snRNP components is observed, while total expression of Snurportin-1 and snRNPs remains unchanged, which demonstrates a functional impact of SNUPN variant in snRNP metabolism. Furthermore, RNA-splicing analysis in patients' muscle showed widespread splicing deregulation, in particular in genes relevant for muscle development and splicing factors that participate in the early steps of spliceosome assembly. In conclusion, we report that SNUPN variants are a new cause of limb girdle muscular dystrophy with specific clinical, histopathological and imaging features, supporting SNUPN as a new gene to be included in genetic testing of myopathies. These results further support the relevance of splicing-related proteins in muscle disorders.

Role of the chemokines RANTES, monocyte chemotactic proteins-3 and -4, and eotaxins-1 and -2 in childhood asthma

Eosinophil recruitment into the airways is a feature of asthma in children. However, the mechanisms by which these cells migrate into the airways are not fully understood. The present study investigated the presence of the eosinophil-activating chemokines regulated on activation, normal T-cell expressed and secreted (RANTES), monocyte chemotactic proteins (MCP)-3 and -4, and eotaxins-1 and -2 in the bronchoalveolar lavage (BAL) fluid obtained from both asthmatic (n=10, age 6-10 yrs) and normal children (n=10, age 5-10 yrs). Measurements of chemokines in BAL fluid showed that levels of RANTES, MCPs-3 and -4, and eotaxins-1 and -2 were significantly increased in fluid obtained from asthmatic children when compared with normal children. Among the different chemokines, RANTES was the cytokine released in greatest quantities in BAL fluid from asthmatic children. There was a significant correlation between the concentrations of MCP-4 and eosinophil numbers in BAL fluid and a trend between both chemokines MCP-3 and eotaxin-2 and eosinophils. Interestingly, the levels of most chemokines correlated with one another. These findings suggest that RANTES monocyte chemotactic proteins-3 and -4, and eotaxins-1 and -2 may regulate eosinophil trafficking into the airways of asthmatic children in a coordinated manner.