High prevalence of congenital deafness on Reunion Island is due to a founder variant of LHFPL5

RIPOR2: A new gene of non-syndromic cochleovestibular dysfunction, discrepancy between human pathology and animal models

Cochleovestibular dysfunctions are rare conditions misrecognized. A homozygous pathogenic variation c.1561C > T (p.Arg521*) in RIPOR2 (RHO family interacting cell polarization regulator 2) has been identified by WES in Tunisian siblings suffering from congenital bilateral profound hearing and vestibular dysfunctions. In contrast to the vestibular areflexia observed in our patients, deaf Ripor2 KO mouse model and our zebrafish model have normal vestibular function.

Case Report: A novel LHFPL3::NTRK2 fusion in dysembryoplastic neuroepithelial tumor

Neurotrophic tyrosine receptor kinase (NTRK) rearrangements are oncogenic drivers of various types of adult and pediatric tumors, including gliomas. However, NTRK rearrangements are extremely rare in glioneuronal tumors. Here, we report a novel NTRK2 rearrangement in a 24-year-old female with dysembryoplastic neuroepithelial tumor (DNT), a circumscribed WHO grade I benign tumor associated with epilepsy. By utilizing targeted RNA next-generation sequencing (NGS), fluorescence in situ hybridization (FISH), reverse transcriptase PCR (RT-PCR), and Sanger sequencing, we verified an in-frame fusion between NTRK2 and the lipoma HMGIC fusion partner-like 3 (LHFPL3). This oncogenic gene rearrangement involves 5' LHFPL3 and 3' NTRK2, retaining the entire tyrosine kinase domain of NTRK2 genes. Moreover, the targeted DNA NGS analysis revealed an IDH1 (p.R132H) mutation, a surprising finding in this type of tumor. The pathogenic mechanism of the LHFPL3::NTRK2 in this case likely involves aberrant dimerization and constitutive activation of RTK signaling pathways.

GM3 synthase deficiency in non-Amish patients

PURPOSE

Biallelic loss-of-function variants in ST3GAL5 cause GM3 synthase deficiency (GM3SD) responsible for Amish infantile epilepsy syndrome. All Amish patients carry the homozygous p.(Arg288Ter) variant arising from a founder effect. To date only 10 patients from 4 non-Amish families have been reported. Thus, the phenotypical spectrum of GM3SD due to other variants and other genetic backgrounds is still poorly known.

METHODS

We collected clinical and molecular data from 16 non-Amish patients with pathogenic ST3GAL5 variants resulting in GM3SD.

RESULTS

We identified 12 families originating from Reunion Island, Ivory Coast, Italy, and Algeria and carrying 6 ST3GAL5 variants, 5 of which were novel. Genealogical investigations and/or haplotype analyses showed that 3 of these variants were founder alleles. Glycosphingolipids quantification in patients' plasma confirmed the pathogenicity of 4 novel variants. All patients (N = 16), aged 2 to 12 years, had severe to profound intellectual disability, 14 of 16 had a hyperkinetic movement disorder, 11 of 16 had epilepsy and 9 of 16 had microcephaly. Other main features were progressive skin pigmentation anomalies, optic atrophy or pale papillae, and hearing loss.

CONCLUSION

The phenotype of non-Amish patients with GM3SD is similar to the Amish infantile epilepsy syndrome, which suggests that GM3SD is associated with a narrow and severe clinical spectrum.