The genetic basis of early-onset hereditary ataxia in Iran: results of a national registry of a heterogeneous population

BACKGROUND

To investigate the genetics of early-onset progressive cerebellar ataxia in Iran, we conducted a study at the Children's Medical Center (CMC), the primary referral center for pediatric disorders in the country, over a three-year period from 2019 to 2022. In this report, we provide the initial findings from the national registry.

METHODS

We selected all early-onset patients with an autosomal recessive mode of inheritance to assess their phenotype, paraclinical tests, and genotypes. The clinical data encompassed clinical features, the Scale for the Assessment and Rating of Ataxia (SARA) scores, Magnetic Resonance Imaging (MRI) results, Electrodiagnostic exams (EDX), and biomarker features. Our genetic investigations included single-gene testing, Whole Exome Sequencing (WES), and Whole Genome Sequencing (WGS).

RESULTS

Our study enrolled 162 patients from various geographic regions of our country. Among our subpopulations, we identified known and novel pathogenic variants in 42 genes in 97 families. The overall genetic diagnostic rate was 59.9%. Notably, we observed PLA2G6, ATM, SACS, and SCA variants in 19, 14, 12, and 10 families, respectively. Remarkably, more than 59% of the cases were attributed to pathogenic variants in these genes.

CONCLUSIONS

Iran, being at the crossroad of the Middle East, exhibits a highly diverse genetic etiology for autosomal recessive hereditary ataxia. In light of this heterogeneity, the development of preventive strategies and targeted molecular therapeutics becomes crucial. A national guideline for the diagnosis and management of patients with these conditions could significantly aid in advancing healthcare approaches and improving patient outcomes.

Expanding the genetic spectrum of giant axonal neuropathy: Two novel variants in Iranian families

BACKGROUND

Giant axonal neuropathy (GAN) is a progressive childhood hereditary polyneuropathy that affects both the peripheral and central nervous systems. Disease-causing variants in the gigaxonin gene (GAN) cause autosomal recessive giant axonal neuropathy. Facial weakness, nystagmus, scoliosis, kinky or curly hair, pyramidal and cerebellar signs, and sensory and motor axonal neuropathy are the main symptoms of this disorder. Here, we report two novel variants in the GAN gene from two unrelated Iranian families.

METHODS

Clinical and imaging data of patients were recorded and evaluated, retrospectively. Whole-exome sequencing (WES) was undertaken in order to detect disease-causing variants in participants. Confirmation of a causative variant in all three patients and their parents was carried out using Sanger sequencing and segregation analysis. In addition, for comparing to our cases, we reviewed all relevant clinical data of previously published cases of GAN between the years 2013-2020.

RESULTS

Three patients from two unrelated families were included. Using WES, we identified a novel nonsense variant [NM_022041.3:c.1162del (p.Leu388Ter)], in a 7-year-old boy of family 1, and a likely pathogenic missense variant [NM_022041.3:c.370T>A (p.Phe124Ile)], in two affected siblings of the family 2. Clinical examination revealed typical features of GAN-1 in all three patients, including walking difficulties, ataxic gait, kinky hair, sensory-motor polyneuropathy, and nonspecific neuroimaging abnormalities. Review of 63 previously reported cases of GAN indicated unique kinky hair, gait problem, hyporeflexia/areflexia, and sensory impairment were the most commonly reported clinical features.

CONCLUSIONS

One homozygous nonsense variant and one homozygous missense variant in the GAN gene were discovered for the first time in two unrelated Iranian families that expand the mutation spectrum of GAN. Imaging findings are nonspecific, but the electrophysiological study in addition to history is helpful to achieve the diagnosis. The molecular test confirms the diagnosis.

Clinical and Molecular Findings of Autosomal Recessive Spastic Ataxia of Charlevoix Saguenay: an Iranian Case Series Expanding the Genetic and Neuroimaging Spectra

Autosomal recessive spastic ataxia of Charlevoix Saguenay (ARSACS) is now increasingly identified from all countries over the world, possibly rendering it one of the most common autosomal recessive ataxias. Here, we selected patients harboring SACS variants, the causative gene for ARSACS, in a large cohort of 137 patients with early-onset ataxia recruited from May 2019 to May 2021 and were referred to the ataxia clinic. Genetic studies were performed for 111 out of 137 patients (81%) which led to a diagnostic rate of 72.9% (81 out of 111 cases). Ten patients with the molecular diagnosis of ARSACS were identified. We investigated the phenotypic and imaging spectra of all confirmed patients with ARSACS. We also estimated the frequency of ARSACS in this cohort and described their clinical and genetic findings including seven novel variants as well as novel neuroimaging findings. While the classic clinical triad of ARSACS is progressive cerebellar ataxia, spasticity, and sensorimotor polyneuropathy, it is not a constant feature in all patients. Sensorimotor axonal-demyelinating neuropathy was detected in all of our patients, but spasticity and extensor plantar reflex were absent in 50% (5/10). In all patients, brain magnetic resonance imaging (MRI) showed symmetric linear hypointensities in the pons (pontine stripes) and anterior superior cerebellar atrophy as well as a hyperintense rim around the thalami (thalamic rim). Although infratentorial arachnoid cyst has been reported in ARSACS earlier, we report anterior temporal arachnoid cyst in two patients for the first time, indicating that arachnoid cyst may be an associated imaging feature of ARSACS. We also extended molecular spectrum of ARSACS by presenting 8 pathogenic and one variant of unknown significance (VUS) sequence variants, which 7 of them have not been reported previously. MetaDome server confirmed that the identified VUS variant was in the intolerant regions of sacsin protein encoded by SACS.