Biallelic variants in the SORD gene are one of the most common causes of hereditary neuropathy among Czech patients.

Recently, biallelic variants in the SORD gene were identified as causal for axonal hereditary neuropathy (HN). We ascertained the spectrum and frequency of SORD variants among a large cohort of Czech patients with unknown cause of HN. Exome sequencing data were analysed for SORD (58 patients). The prevalent c.757del variant was tested with fragment analysis (931 patients). Sanger sequencing in additional 70 patients was done. PCR primers were designed to amplify the SORD gene with the exclusion of the pseudogene SORD2P. Sequence differences between gene and pseudogene were identified and frequencies of SNPs were calculated. Eighteen patients from 16 unrelated families with biallelic variants in the SORD gene were found and the c.757del was present in all patients on at least one allele. Three novel, probably pathogenic, variants were detected, always in a heterozygous state in combination with the c.757del on the second allele. Patients presented with a slowly progressive axonal HN. Almost all patients had moderate pes cavus deformity. SORD neuropathy is frequent in Czech patients and the third most common cause of autosomal recessive HN. The c.757del is highly prevalent. Specific amplification of the SORD gene with the exclusion of the pseudogene is essential for a precise molecular diagnostics.

Novel SBF2 mutations and clinical spectrum of Charcot-Marie-Tooth neuropathy type 4B2.

Biallelic SBF2 mutations cause Charcot-Marie-Tooth disease type 4B2 (CMT4B2), a sensorimotor neuropathy with autosomal recessive inheritance and association with glaucoma. Since the discovery of the gene mutation, only few additional patients have been reported. We identified seven CMT4B2 families with nine different SBF2 mutations. Revisiting genetic and clinical data from our cohort and the literature, SBF2 variants were private mutations, including exon-deletion and de novo variants. The neuropathy typically started in the first decade after normal early motor development, was predominantly motor and had a rather moderate course. Electrophysiology and nerve biopsies indicated demyelination and excess myelin outfoldings constituted a characteristic feature. While neuropathy was >90% penetrant at age 10 years, glaucoma was absent in ~40% of cases but sometimes developed with age. Consequently, SBF2 mutation analysis should not be restricted to individuals with coincident neuropathy and glaucoma, and CMT4B2 patients without glaucoma should be followed for increased intraocular pressure. The presence of exon-deletion and de novo mutations demands comprehensive mutation scanning and family studies to ensure appropriate diagnostic approaches and genetic counseling.

Mutations in HINT1 are one of the most frequent causes of hereditary neuropathy among Czech patients and neuromyotonia is rather an underdiagnosed symptom.

Mutations in the HINT1 gene were recently discovered as being the major cause of autosomal recessive axonal neuropathy with neuromyotonia. This combination was clinically recognized and described previously in a few reports but is generally unknown. We aimed to establish the importance of HINT1 mutations as the cause of hereditary neuropathy and particularly hereditary motor neuropathy/axonal Charcot-Marie-Tooth (HMN/CMT2) among Czech patients. Overall, mutations in the HINT1 gene seem to be a surprisingly frequent cause of inherited neuropathy in our group of patients. Biallelic pathogenic mutations were found in 21 patients from 19 families. The prevalent mutation in the Czech population is the p.R37P (95% of pathogenic alleles). Clinically, all patients with biallelic mutations presented with early onset of symptoms at the end of the first decade. Foot/toe extension weakness to plegia was present in almost all patients. Neuromyotonia was present in all but two patients. However, it had been properly recognized in only three patients prior to molecular genetic diagnosis. HINT1 mutations seem to be one of the most frequent causes of inherited neuropathy and are probably the most frequent cause of HMN in Czech patients. We suggest all HMN/CMT2 patients be tested for the presence of the prevalent mutation, the p.R37P.

Monitoring of methylation changes in 9p21 region in patients with myelodysplastic syndromes and acute myeloid leukemia.

Epigenetic de novo methylation of CpG islands is an important event in malignant transformation. Two genes are frequently methylated: cyclin-dependent kinase inhibitor 2B (CDKN2B) and cyclin-dependent kinase inhibitor 2A (CDKN2A). In our study methylation of these genes was studied in 63 patients with myelodysplastic syndromes (MDS), 2 with myelodysplastic/myeloproliferative neoplasms (MDS/MPN) and 13 with acute myeloid leukemia (AML). Five patients were monitored during 5-azacytidine treatment. Twenty-six healthy donors were tested in a control group. Methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA) method with all associated techniques was used for detection. Aberrant methylation was present in the CDKN2A gene in 38% and in the CDKN2B gene in 77% of the patients in MDS group. The level of methylation was higher in the group of AML patients - 77% in CDKN2A gene and 100% in CDKN2B gene. In MDS patients, an aberrant methylation was associated with a tendency to disease progression towards more advanced forms according to the World Health Organization (WHO) classification and the International Prognostic Scoring System (IPSS). Significant differences in methylation level were observed between early and advanced forms of MDS in CDKN2B gene (P value < 0.05) but not for CDKN2A gene. The trend of methylation in patients treated with azacitidine was analyzed in CDKN2B gene and correlated with the course of the disease. Increased methylation was connected with disease progression. We concluded that the methylation level of CDKN2B gene might be used as a marker of leukemic transformation in MDS. Our study indicates the role of hypermethylation as an important event in the progression of MDS to AML.

High frequency of SH3TC2 mutations in Czech HMSN I patients.

Charcot-Marie-Tooth (CMT) neuropathy type 4C (CMT4C) is an autosomal recessive (AR), demyelinating neuropathy with early spine deformities caused by mutations in the SH3TC2 gene. To determine the spectrum of SH3TC2 mutations in the Czech population, the entire coding region of SH3TC2 was sequenced in 60 unrelated Czech patients. The prevalent mutation was shown to be the p.Arg954Stop. Therefore, 412 additional patients referred for CMT testing were tested for the presence of p.Arg954Stop only. Of 60 patients in whom the SH3TC2 gene was sequenced, at least one mutation was detected in 13 (21.7%) patients and biallelic pathogenic mutations were detected in 7 (11.6%) patients. Of the 412 patients tested for p.Arg954Stop, the mutation was found in 8 patients (1.94%), 6 were homozygous and 2 were heterozygous. The second causative mutation was detected by sequencing in one of the patients but not in the other. Nine novel sequence variants were detected. Their pathogenicity was further tested in silico and in control samples. Mutations in the SH3TC2 gene are a frequent cause of demyelinating hereditary neuropathy among Czech patients. In total, at least one mutation was found in 21 unrelated patients. CMT4C seems to be the most frequent type of AR CMT and one of the most frequent of all CMT types. Mutation p.Arg954Stop is highly prevalent in the Czech population. Patients with demyelinating neuropathy along with non-dominant mode of inheritance and negative for CMT1A/hereditary neuropathy with liability to pressure palsy should be tested for the presence of the p.Arg954Stop mutation or other mutations in the SH3TC2 gene.