Justine Lerat

In normal activated B-cells, Activation Induced-cytidine deaminase (AID) is absolutely required for immunoglobulin (Ig) class switch recombination (CSR) and IGHV somatic hypermutation (SHM). AID is also implicated in the Locus Suicide Recombination (LSR) of the Ig heavy (IgH) locus, resulting in the deletion of the IgH constant part. Chronic lymphocytic leukemia (CLL) is an indolent non-Hodgkin B-cell lymphoma characterized by tumor CLL B-cells that weakly express a B cell receptor (BCR) on their surface. The great majority of CLL tumor B-cells are non class-switched. Searching for abnormalities of IgH locus recombination in CLL, we investigated CSR and LSR in samples from CLL patients (N=47) with high blood tumor cell infiltration (>98%) and in healthy volunteers (HV) as controls (N=9). LSR was detectable at comparable levels in both HV and CLL groups. CSR counts were decreased in CLL samples as expected. As distribution of LSR counts was bimodal, we separated CLL patients in two groups so called LSR ^High and LSR ^Low . LSR ^High CLLs exhibited very weak AID expression and low mutation rate of IgHV region and of the AID off-target PIM1 gene. LSR junction diversity, evaluated using the Shannon index, was increased in LSR ^High CLLs suggesting that LSR was on-going in these cells. Also, shorter telomeres were observed in LSR ^High CLLs suggesting an increased number of past mitosis. Consistently, increased levels of cMYC expression were detected in LSR ^High CLLs and treatment free survival of these cases was markedly decreased. We hypothesized that LSR in LSR ^High CLLs is AID independent and could be due to DNA lesion and inaccurate DSB repair within the IgH locus, which could be accessible to recombination machinery due to increased IgH locus transcription. Altogether, our results indicate the accessibility of IgH locus and the proliferation increase LSR rate in LSR ^High CLLs could be related to cMYC resulting in shorter treatment free survival of patients and point on an AID independent mechanism of IgH recombination.

Background: The most common inherited peripheral neuropathy is Charcot‐Marie‐Tooth disease (CMT), with a prevalence of 1/2500. Other symptoms can be associated to the condition, such as hearing loss. Currently, no global hearing impairment assessment has been determined, and the physiopathology is not well known.Methods: The aim of the study was to analyze among a French series of 3,412 patients with inherited peripheral neuropathy (IPN), the ones who also suffer from hearing loss, to establish phenotype‐genotype correlations. An NGS strategy for IPN one side and nonsyndromic hearing loss (NSHL) on the other side, were performed.Results: Hearing loss (HL) was present in only 44 patients (1.30%). The clinical data of 27 patients were usable. Demyelinating neuropathy was diagnosed in 15 cases and axonal neuropathy in 12 cases. HL varied from mild to profound. Five cases of auditory neuropathy were noticed. Diagnosis was made for 60% of these patients. Seven novel pathogenic variants were discovered in five different genes: PRPS1; MPZ; SH3TC2; NEFL; and ABHD12. Two patients with PMP22 variant, had also an additional variant in COCH and MYH14 respectively. No pathogenic variant was found at the DFNB1 locus. Genotype‐phenotype correlations do exist, especially with SH3TC2, PRPS1, ABHD12, NEFL, and TRPV4.Conclusion: Involvement of PMP22 is not enough to explain hearing loss in patients suffering from IPN. HL can be due to cochlear impairment and/or auditory nerve dysfunction. HL is certainly underdiagnosed, and should be evaluated in every patient suffering from IPN.

Background: CMTX5 is characterized by peripheral neuropathy, early‐onset sensorineural hearing impairment, and optic neuropathy. Only seven variants have been reported and no genotype‐phenotype correlations have yet been established. PRPS1 has a crystallographic structure, as it is composed of three dimers that constitute a hexamer.Methods: Next‐generation sequencing (NGS) was performed using a custom 92‐gene panel designed for the diagnosis of Charcot‐Marie‐Tooth (CMT) and associated neuropathies.Results: We report the case of a 35‐year‐old male, who had presented CMT and hearing loss since childhood associated to bilateral optic neuropathy without any sign of retinitis pigmentosa. A new hemizygous variant on chromosomic position X:106,882,604, in the PRPS1 gene, c.202A > T, p.(Met68Leu) was found. This change is predicted to lead to an altered affinity between the different subunits in the dimer, thereby may prevent the hexamer formation.Conclusion: CMTX5 is probably under‐diagnosed, as an overlap among the different features due to PRPS1 exists. Patients who developed polyneuropathy associated to sensorineural deafness and optic atrophy during childhood should be assessed for PRPS1.

Neurofilaments are neuron‐specific intermediate filaments essential for the radial growth of axons during development and the maintenance of axonal diameter. Pathogenic variants of NEFL are associated with CMT1F, CMT2E, and CMTDIG and have been observed in less than 1% of CMT cases, resulting in the reporting of 35 variants in 173 CMT patients to date. However, only six variants have been reported in 17 patients with impaired hearing. No genotype‐phenotype correlations have yet been established. Here, we report an additional case: a 69‐year‐old female, who originally presented with axonal sensory and motor neuropathy at the age of 45, associated with moderate sensorineural hearing loss, with a slight slope at high frequencies. NGS identified a novel pathogenic variant: c.269A>G, p.(Glu90Gly). Hearing impairment is often linked to CMT due to pathogenic variants of NEFL, especially p.(Glu90Lys) and p.(Asn98Ser), and in our case p.(Glu90Gly). These pathogenic variants are all located at hot spots, in the head domain and the two ends of the rod domain of the protein.

Reunion Island is a French oversea department in the Indian Ocean with 1.6/1000, an estimated prevalence of deafness that is almost double as compared to the mainland France. Twelve children having isolated bilateral prelingual profound deafness along with motor delay attributed to vestibular areflexia were enrolled. Their mean walking age was 19 months. Electroretinography and temporal bone CT‐scans were normal in all cases. A novel homozygous frameshift lipoma HMGIC fusion partner‐like 5 (LHFPL5) variant c.185delT p.(Phe62Serfs*23) was identified using whole‐exome sequencing. It was found in seven families. Four patients from two different families from both Reunion Island and mainland France, were compound heterozygous: c.185delT p.(Phe62Serfs*23) and c.472C > T p.(Arg158Trp). The phenotype observed in our patients completely mimics the hurry‐scurry (hscy) murine Tmhs knock‐out model. The recurrent occurrence of same LHFPL5 variant in Reunion Island is attributed to common ancestor couple born in 1693.