Background Charcot‐Marie‐Tooth (CMT) disease is a very heterogeneous neurological condition with more than 90 reported genetic entities. It is the most common inherited peripheral neuropathy; however, cases are rarely reported in sub‐Saharan Africa. In addition, only few families, mostly of Caucasian ancestry, have been reported to have Charcot‐Marie‐Tooth disease type 2D (CMT2D) mutations. To date no case of CMT2D was reported in Africa. We present here a consanguineous family with CMT phenotype in which a novel mutation in the GARS (glycyl‐tRNA synthetase) gene was identified. Methods Patients were examined thoroughly and nerve conduction studies (NCS) were performed. DNA from the proband was used for CMT gene panel testing (including 50 genes, PMP22 duplication and mtDNA ). Putative mutations were verified in all available family members to check for segregation. Results Two individuals, a male and a female, were found to be affected. Symptoms started in their teenage years with muscle weakness and atrophy in hands. Later, distal involvement of the lower limbs was noticed. Patients complained of minor sensory impairment. NCS showed no response in the upper as well as the lower limbs. Genetic testing surprisingly identified a novel heterozygous missense mutation c.794C>A (p.Ser265Tyr) in the GARS gene associated with CMT2D. This variant segregated with the disease in the family and was also seen in the mother who presented no symptoms. Conclusion This is the first report of a genetically confirmed CMT2D case in Africa, expanding its genetic epidemiology. Increasing access to genetic testing may reveal more novel CMT variants or genes in the African population that could be relevant to other populations and further our understanding of their mechanism.
Objective: Primary hypobetalipoproteinemia is characterized by LDL-C (low-density lipoprotein cholesterol) concentrations below the fifth percentile. Primary hypobetalipoproteinemia mostly results from heterozygous mutations in the APOB and PCSK9 genes, and a polygenic origin is hypothesized in the remaining cases. Hypobetalipoproteinemia patients present an increased risk of nonalcoholic fatty liver disease and steatohepatitis. Here, we compared hepatic alterations between monogenic, polygenic, and primary hypobetalipoproteinemia of unknown cause. Approach and Results: Targeted next-generation sequencing was performed in a cohort of 111 patients with hypobetalipoproteinemia to assess monogenic and polygenic origins using an LDL-C-dedicated polygenic risk score. Forty patients (36%) had monogenic hypobetalipoproteinemia, 38 (34%) had polygenic hypobetalipoproteinemia, and 33 subjects (30%) had hypobetalipoproteinemia from an unknown cause. Patients with monogenic hypobetalipoproteinemia had lower LDL-C and apolipoprotein B plasma levels compared with those with polygenic hypobetalipoproteinemia. Liver function was assessed by hepatic ultrasonography and liver enzymes levels. Fifty-nine percent of patients with primary hypobetalipoproteinemia presented with liver steatosis, whereas 21% had increased alanine aminotransferase suggestive of liver injury. Monogenic hypobetalipoproteinemia was also associated with an increased prevalence of liver steatosis (81% versus 29%, P <0.001) and liver injury (47% versus 0%) compared with polygenic hypobetalipoproteinemia. Conclusions: This study highlights the importance of genetic diagnosis in the clinical care of primary hypobetalipoproteinemia patients. It shows for the first time that a polygenic origin of hypobetalipoproteinemia is associated with a lower risk of liver steatosis and liver injury versus monogenic hypobetalipoproteinemia. Thus, polygenic risk score is a useful tool to establish a more personalized follow-up of primary hypobetalipoproteinemia patients.
X‐linked Charcot‐Marie‐Tooth type 1 (CMTX1) disease is one of the most common subtypes of inherited neuropathies and is caused by mutations in the GJB1 gene. To date, more than 400 mutations have been reported in GJB1 worldwide but none in sub‐Saharan Africa (SSA). We aimed to clinically characterize patients with CMTX1 and identify the genetic defects. All patients were examined thoroughly, and Nerve Conduction Studies (NCS) were done. EEG and pure tone audiometry (PTA) were also done in select individuals having additional symptoms. DNA was extracted for CMT gene panel testing (50 genes + mtDNA and PMP22 duplication), and putative variants were screened in available relatives. The predominant starting symptom was tingling, and the chief complaint was gait difficulty. Neurological examination found a distal muscle weakness and atrophy, and sensory loss, skeletal deformities, decreased or absent reflexes and steppage gait. The inheritance pattern was consistent with dominant X‐linked. NCS showed no response in most of the tested nerves in lower limbs, and normal or reduced amplitudes in upper limbs. A severe sensorineural hearing impairment and a focal epileptic seizure were observed in one patient each. A high intra and inter‐familial clinical variability was observed. Genetic testing found three pathogenic missense variants in GJB1, one in each of the families (Val91Met, Arg15Trp, and Phe235Cys). This is the first report of genetically confirmed cases of CMTX1 in SSA, and confirms its clinical and genetic heterogeneity.
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