HSMNR belongs to the most frequent types of hereditary neuropathy in the Czech Republic and is twice more frequent than HMSNL

The Hexokinase 1 5'-UTR Mutation in Charcot-Marie-Tooth 4G Disease Alters Hexokinase 1 Binding to Voltage-Dependent Anion Channel-1 and Leads to Dysfunctional Mitochondrial Calcium Buffering

Demyelinating Charcot-Marie-Tooth 4G (CMT4G) results from a recessive mutation in the 5'UTR region of the Hexokinase 1 (HK1) gene. HK participates in mitochondrial calcium homeostasis by binding to the Voltage-Dependent Anion Channel (VDAC), through its N-terminal porin-binding domain. Our hypothesis is that CMT4G mutation results in a broken interaction between mutant HK1 and VDAC, disturbing mitochondrial calcium homeostasis. We studied a cohort of 25 CMT4G patients recruited in the French gypsy population. The disease was characterized by a childhood onset, an intermediate demyelinating pattern, and a significant phenotype leading to becoming wheelchair-bound by the fifth decade of life. Co-IP and PLA studies indicated a strong decreased interaction between VDAC and HK1 in the patients' PBMCs and sural nerve. We observed that either wild-type HK1 expression or a peptide comprising the 15 aa of the N-terminal wild-type HK1 administration decreased mitochondrial calcium release in HEK293 cells. However, mutated CMT4G HK1 or the 15 aa of the mutated HK1 was unable to block mitochondrial calcium release. Taken together, these data show that the CMT4G-induced modification of the HK1 N-terminus disrupts HK1-VDAC interaction. This alters mitochondrial calcium buffering that has been shown to be critical for myelin sheath maintenance.

Expanding the Molecular Spectrum of HK1-Related Charcot-Marie-Tooth Disease, Type 4G; the First Report in Iran

Charcot-Marie-Tooth disease type 4G (CMT4G) was first reported in Balkan Gypsies as a myelinopathy starting with progressive distal lower limb weakness, followed by upper limb involvement and prominent distal sensory impairment later in the patient's life. So far, CMT4G has been only reported in European Roma communities with two founder homozygous variants; g.9712G>C and g.11027G>A, located in the 5'-UTR of the HK1 gene. Here, we present the first Iranian CMT4G patient manifesting progressive distal lower limb weakness from 11 years of age and diagnosed with chronic demyelinating sensorimotor polyneuropathy. Whole-exome sequencing for this patient revealed a homozygous c.19C>T (p. Arg7*) variant in the HK1 gene. This report expands the mutational spectrum of the HK1-related CMT disorder and provides supporting evidence for the observation of CMT4G outside the Roma population. Interestingly, the same Arg7* variant is recently observed in another unrelated Pakistani CMT patient, proposing a possible prevalence of this variant in the Middle Eastern populations.

Variant c.2158-2A>G in MANBA is an important and frequent cause of hereditary hearing loss and beta-mannosidosis among the Czech and Slovak Roma population- evidence for a new ethnic-specific variant

Background

The Roma are a European ethnic minority threatened by several recessive diseases.

Variants in MANBA cause a rare lysosomal storage disorder named beta-mannosidosis whose clinical manifestation includes deafness and mental retardation. Since 1986, only 23 patients with beta-mannosidosis and biallelic MANBA variants have been described worldwide.

Results

We now report on further 10 beta-mannosidosis patients of Roma origin from eight families in the Czech and Slovak Republics with hearing loss, mental retardation and homozygous pathogenic variants in MANBA.

MANBA variant c.2158-2A>G screening among 345 anonymized normal hearing controls from Roma populations revealed a carrier/heterozygote frequency of 3.77%. This is about 925 times higher than the frequency of this variant in the gnomAD public database and classifies the c.2158-2A>G variant as a prevalent, ethnic-specific variant causing hearing loss and mental retardation in a homozygous state. The frequency of heterozygotes/carriers is similar to another pathogenic variant c.71G>A (p.W24*) in GJB2, regarded as the most frequent variant causing deafness in Roma populations.

Conlcusion

Beta-mannosidosis, due to a homozygous c.2158-2A>G MANBA variant, is an important and previously unknown cause of hearing loss and mental retardation among Central European Roma.

Two types of recessive hereditary spastic paraplegia in Roma patients in compound heterozygous state; no ethnically prevalent variant found

Hereditary spastic paraplegia (HSP or SPG) is a group of rare upper motor neuron diseases. As some ethnically-specific, disease-causing homozygous variants were described in the Czech Roma population, we hypotesised that some prevalent HSP-causing variant could exist in this population. Eight Czech Roma patients were found in a large group of Czech patients with suspected HSP and were tested using gene panel massively parallel sequencing (MPS). Two of the eight were diagnosed with SPG11 and SPG77, respectively. The SPG77 patient manifests a pure HSP phenotype, which is unusual for this SPG type. Both patients are compound heterozygotes for two different variants in the SPG11 (c.1603-1G>A and del ex. 16-18) and FARS2 (c.1082C>T and del ex.1-2) genes respectively; the three variants are novel. In order to find a potential ethnically-specific, disease-causing variant for HSP, we tested the heterozygote frequency of these variants among 130 anonymised DNA samples of Czech Roma individuals without clinical signs of HSP (HPS-negative). A novel deletion of ex.16-18 in the SPG11 gene was found in a heterozygous state in one individual in the HSP-negative group. Haplotype analysis showed that this individual and the patient with SPG11 shared the same haplotype. This supports the assumption that the identified SPG11 deletion could be a founder mutation in the Czech Roma population. In some Roma patients the disease may also be caused by two different biallelic pathogenic mutations.

HMSN Lom in 12 Czech patients, with one unusual case due to uniparental isodisomy of chromosome 8

Hereditary motor and sensory neuropathy-type Lom (HMSNL), also known as CMT4D, a demyelinating neuropathy with late-onset deafness is an autosomal recessive disorder threatening Roma population worldwide. The clinical phenotype was reported in several case reports before the gene discovery. HMSNL is caused by a homozygous founder mutation p.Arg148* in the N-Myc downstream-regulated gene 1. Here, we report findings from the Czech Republic, where HMSNL was found in 12 Czech patients from eight families. In these 12 patients, 11 of the causes were due to p.Arg148* mutation inherited from both parents by the autosomal recessive mechanism. But in one case, the recessive mutation was inherited only from one parent (father) and unmasked owing to an uniparental isodisomy of the entire chromosome eight. The inherited peripheral neuropathy owing to an isodisomy of the whole chromosome pointed to an interesting, less frequent possibility of recessive disease and complications with genetic counseling.