Plasma neurofilament light chain level is not a biomarker of Charcot-Marie-Tooth disease progression: Results of 3-year follow-up study.

BACKGROUND AND PURPOSE: Charcot-Marie-Tooth disease (CMT) is a hereditary, slowly progressive neuropathy. Currently, there are no effective pharmacological treatments or sensitive disease activity biomarkers available. The aim of this study was to demonstrate the change in plasma neurofilament light chain (NfL) over time in a CMT cohort and analyse the association between CMT severity and NfL level. METHODS: Initially, 101 CMT patients and 64 controls were enrolled in the study. Repeated evaluation was performed in 73 patients and 28 controls at a 3-year interval. Disease severity assessment included clinical evaluation with CMT Neuropathy Score version 2 (CMTNSv2). Plasma NfL concentration was measured using the Simoa (single molecule array) NfL assay. RESULTS: Plasma NfL concentration was increased in the CMT group compared with controls (p < 0.001). Overall NfL level increased over the 3-year interval in both CMT (p = 0.012) and control (p = 0.001) groups. However, in 22 of 73 CMT patients and seven of 28 controls, the NfL level decreased from the baseline. Analysing the association between 3-year change in plasma NfL and disease severity (CMTNSv2), there was no correlation in the CMT group (r = 0.228, p = 0.052) or different CMT subgroups. CONCLUSIONS: Our study verifies increased plasma NfL concentrations in patients with CMT compared with controls. Longitudinal 3-year data showed a variable change in NfL levels between CMT subtypes. There was no association between change in NfL over time and disease severity. These findings suggests that NfL is not a biomarker for CMT progression.

Missense variants in ANKRD11 cause KBG syndrome by impairment of stability or transcriptional activity of the encoded protein.

PURPOSE: Although haploinsufficiency of ANKRD11 is among the most common genetic causes of neurodevelopmental disorders, the role of rare ANKRD11 missense variation remains unclear. We characterized clinical, molecular, and functional spectra of ANKRD11 missense variants. METHODS: We collected clinical information of individuals with ANKRD11 missense variants and evaluated phenotypic fit to KBG syndrome. We assessed pathogenicity of variants through in silico analyses and cell-based experiments. RESULTS: We identified 20 unique, mostly de novo, ANKRD11 missense variants in 29 individuals, presenting with syndromic neurodevelopmental disorders similar to KBG syndrome caused by ANKRD11 protein truncating variants or 16q24.3 microdeletions. Missense variants significantly clustered in repression domain 2 at the ANKRD11 C-terminus. Of the 10 functionally studied missense variants, 6 reduced ANKRD11 stability. One variant caused decreased proteasome degradation and loss of ANKRD11 transcriptional activity. CONCLUSION: Our study indicates that pathogenic heterozygous ANKRD11 missense variants cause the clinically recognizable KBG syndrome. Disrupted transrepression capacity and reduced protein stability each independently lead to ANKRD11 loss-of-function, consistent with haploinsufficiency. This highlights the diagnostic relevance of ANKRD11 missense variants, but also poses diagnostic challenges because the KBG-associated phenotype may be mild and inherited pathogenic ANKRD11 (missense) variants are increasingly observed, warranting stringent variant classification and careful phenotyping.

Kohlschütter-Tönz syndrome: Case report with novel feature and detailed review of features associated with ROGDI variants.

Kohlschütter-Tönz syndrome (KTS) is a rare, autosomal recessive syndrome characterized by a triad of epilepsy, amelogenesis imperfecta and severe global developmental delay. It was first described in a Swiss family in 1974 by Alfried Kohlschütter and Otmar Tönz. It is caused by pathogenic variants in the ROGDI gene. To the best of our knowledge, there are currently 43 patients with a confirmed ROGDI gene pathogenic variant reported. Here, we review in detail the clinical manifestations of KTS, provide an overview of all reported genetically confirmed patients, and document an additional case of KTS-a 6-year-old Latvian girl-with a confirmed ROGDI gene pathogenic variant. In contrast to previous reports, we detected idiopathic bilateral nephrocalcinosis in this newly identified KTS patient. Perampanel proved an effective treatment for our patient with prolonged super-refractory status epilepticus. In order to better characterize this rare syndrome and its clinical course, it is important to report any additional symptoms and also the effectiveness of used therapies. Future research should focus on elucidating the mechanisms by which the absence/insufficiency of ROGDI-encoded protein causes the clinical manifestations of KTS. This knowledge could shape possible ways of influencing the disease's natural history with more effective therapies.

Plasma neurofilament light chain as a potential biomarker in Charcot-Marie-Tooth disease.

BACKGROUND AND PURPOSE: Charcot-Marie-Tooth (CMT) disease is a chronic, slowly progressing disorder. The lack of specific disease progression biomarkers limits the execution of clinical trials. However, neurofilament light chain (NfL) has been suggested as a potential biomarker for peripheral nervous system disorders. METHODS: Ninety-six CMT disease patients and 60 healthy controls were enrolled in the study. Disease severity assessment included clinical evaluation with CMT Neuropathy Score version 2 (CMTNSv2). Blood plasma NfL concentrations were measured using the single-molecule array NfL assay. RESULTS: The NfL concentration was significantly higher in the CMT disease patient group than in the controls (p < 0.001). Of the CMT disease patients, those with type CMTX1 had a higher NfL level than those in the two other analysed subgroups (CMT1A and other CMT disease types) (p = 0.0498). The NfL concentration had a significant but weak correlation with the CMTNSv2 (rs  = 0.25, p = 0.012). In one CMT disease patient with an extremely elevated NfL level, overlap with chronic inflammatory demyelinating polyneuropathy was suspected. Receiver operating characteristic analysis showed that an NfL concentration of 8.9 pg/ml could be used to discriminate CMT disease patients from controls, with an area under the curve of 0.881. CONCLUSIONS: Our study confirmed that the plasma NfL concentration is significantly higher in CMT disease patients than in controls. Plasma NfL concentration was found to significantly, albeit weakly, reflect the clinical severity of CMT disease. In the future, NfL may be used, either individually or collaboratively, as a biomarker in the clinical context of suspected CMT disease; however, several issues need to be addressed first.

Alanyl-tRNA Synthetase 1 Gene Variants in Hereditary Neuropathy: Genotype and Phenotype Overview.

Background and Objectives: Our objective was to report 2 novel variants and to reclassify previously reported alanyl-tRNA synthetase 1 (AARS1) variants associated with hereditary neuropathy and to summarize the clinical features of a previously published cohort of patients. Methods: We performed detailed neurologic and electrophysiologic assessments and segregation analysis of 2 unrelated families with Charcot-Marie-Tooth (CMT) disease with novel variants in the AARS1 gene. Via literature search, we found studies that included neuropathy cases with AARS1 variants; we then reviewed and reclassified these variants. Results: We identified 2 CMT families harboring previously unreported likely pathogenic AARS1 variants: c.1823C>A p.(Thr608Lys) and c.1815C>G p.(His605Gln). In addition, we reinterpreted a total of 35 different AARS1 variants reported in cases with neuropathy from the literature: 9 variants fulfilled the current criteria for being (likely) pathogenic. We compiled and summarized standardized clinical and genotypic information for 90 affected individuals from 32 families with (likely) pathogenic AARS1 variants. Most experienced motor weakness and sensory loss in the lower limbs. Discussion: In total, 11 AARS1 variants can currently be classified as pathogenic or likely pathogenic and are associated with sensorimotor axonal or intermediate, slowly progressive polyneuropathy with common asymmetry and variable age of symptom onset with no apparent involvement of other organ systems.