Compound heterozygous variants in MAPK8IP3 were detected in severe congenital hypotonia mimicking lethal spinal muscular atrophy

Mitogen-activated protein kinase 8-interacting protein 3 gene (MAPK8IP3) encodes the c-Jun-amino-terminal kinase-interacting protein 3 (JIP3) and is involved in retrograde axonal transport. Heterozygous de novo pathogenic variants in MAPK8IP3 result in a neurodevelopmental disorder with or without brain abnormalities and possible axonal peripheral neuropathy. Whole-exome sequencing was performed on an individual presenting with severe congenital muscle hypotonia of neuronal origin mimicking lethal spinal muscular atrophy. Compound heterozygous rare variants (a splice and a missense) were detected in MAPK8IP3, inherited from the healthy parents. Western blot analysis in a muscle biopsy sample showed a more than 60% decrease in JIP3 expression. Here, we suggest a novel autosomal recessive phenotype of a lower motor neuron disease caused by JIP3 deficiency.

Utilisation of fluorescent multiplex PCR and laser-induced capillary electrophoresis for the diagnosis of Ewing family of tumours in formalin-fixed paraffin-embedded tissues

AIMS

The localisation of the translocation breakpoint of the Ewing sarcoma family of tumours shows significant variability on relatively large regions of fusion partner genes. As a consequence, many alternative forms of EWSR1-ETS translocation exist which make the RNA-based molecular diagnostics of Ewing sarcoma family of tumours complicated. In addition to the heterogeneity of fusion transcripts, the degradation of RNA also presents a significant difficulty in the molecular analysis of formalin-fixed paraffin-embedded (FFPE) tissues. Our aim was to establish a sensitive method which is able to identify all combinatorially possible EWSR1-FLI1 and EWSR1-ERG translocation transcripts in FFPE tissue samples despite significant RNA-degradation.

METHODS

The combination of fluorescent multiplex PCR with laser-induced capillary electrophoresis was used to detect and identify EWSR1-FLI1 and EWSR1-ERG chimeric transcripts on the basis of amplicon size, and forward primers labelled by distinct fluorophores.

RESULTS

Using this method, we processed 60 FFPE samples of Ewing sarcoma family of tumours, and identified six types EWSR1-FLI1 and one type EWSR1-ERG chimeric transcripts acceptable for RT-PCR analysis in 27 out of 45 samples. This result shows 60% sensitivity for detecting the most frequent Ewing family of tumour (EFT)-related fusion transcripts.

CONCLUSIONS

The utilisation of fluorescent multiplex PCR and laser-induced fluorescent capillary electrophoresis is effective for the diagnosis of EFT in FFPE tissue, and after the defined modifications it can offer a sensitive method to overcome the diagnostic difficulties connected with heterogeneity of the variant translocations in EFT.