Anticipation Can Be More Common in Hereditary Spastic Paraplegia with SPAST Mutations Than It Appears.

BACKGROUND AND OBJECTIVE: Hereditary spastic paraplegia (HSP) is a heterogeneous neurodegenerative disorder with lower-limb spasticity and weakness. Different patterns of inheritance have been identified in HSP. Most autosomal-dominant HSPs (AD-HSPs) are associated with mutations of the SPAST gene (SPG4), leading to a pure form of HSP with variable age-at-onset (AAO). Anticipation, an earlier onset of disease, as well as aggravation of symptoms in successive generations, may be correlated to SPG4. Herein, we suggested that anticipation might be a relatively common finding in SPG4 families. METHODS: Whole-exome sequencing was done on DNA of 14 unrelated Iranian AD-HSP probands. Data were analyzed, and candidate variants were PCR-amplified and sequenced by the Sanger method, subsequently checked in family members to co-segregation analysis. Multiplex ligation-dependent probe amplification (MLPA) was done for seven probands. Clinical features of the probands were recorded, and the probable anticipation was checked in these families. Other previous reported SPG4 families were investigated to anticipation. RESULTS: Our findings showed that SPG4 was the common subtype of HSP; three families carried variants in the KIF5A, ATL1, and MFN2 genes, while five families harbored mutations in the SPAST gene. Clinical features of only SPG4 families indicated decreasing AAO in affected individuals of the successive generations, and this difference was significant (p-value <0.05). CONCLUSION: It seems SPAST will be the first candidate gene in families that manifests a pure form of AD-HSP and anticipation. Therefore, it may be a powerful situation of genotype-phenotype correlation. However, the underlying mechanism of anticipation in these families is not clear yet.

Neurodegeneration with Brain Iron Accumulation and a Brief Report of the Disease in Iran.

Neurodegeneration with brain iron accumulation (NBIA) is a term used for a group of hereditary neurological disorders with abnormal accumulation of iron in basal ganglia. It is clinically and genetically heterogeneous with symptoms such as dystonia, dysarthria, Parkinsonism, intellectual disability, and spasticity. The age at onset and rate of progression are variable among individuals. Current therapies are exclusively symptomatic and unable to hinder the disease progression. Approximately 16 genes have been identified and affiliated to such condition with different functions such as iron metabolism (only two genes: Ferritin Light Chain (FTL) Ceruloplasmin (CP)), lipid metabolism, lysosomal functions, and autophagy process, but some functions have remained unknown so far. Subgroups of NBIA are categorized based on the mutant genes. Although in the last 10 years, the development of whole-exome sequencing (WES) technology has promoted the identification of disease-causing genes, there seem to be some unknown genes and our knowledge about the molecular aspects and pathogenesis of NBIA is not complete yet. There is currently no comprehensive study about the NBIA in Iran; however, one of the latest discovered NBIA genes, GTP-binding protein 2 (GTPBP2), has been identified in an Iranian family, and there are some patients who have genetically remained unknown.

Description of clinical features and genetic analysis of one ultra-rare (SPG64) and two common forms (SPG5A and SPG15) of hereditary spastic paraplegia families.

Hereditary spastic paraplegia (HSP) is a clinically and genetically heterogeneous neurodegenerative disorder, characterized by lower-limb spasticity and weakness. To date, more than 82 loci/genes (SPG1-SPG82) have been identified that contribute to the cause of HSP. Despite the use of next-generation sequencing-based methods, genetic-analysis has failed in the finding of causative genes in more than 50% of HSP patients, indicating a more significant heterogeneity and absence of a given phenotype-genotype correlation. Here, we performed whole-exome sequencing (WES) to identify HSP-causing genes in three unrelated-Iranian probands. Candidate variants were detected and confirmed in the probands and co-segregated in the family members. The phenotypic data gathered and compared with earlier cases with the same sub-types of disease. Three novel homozygous variants, c.978delT; p.Q327Kfs*39, c.A1208G; p.D403G and c.3811delT; p.S1271Lfs*44, in known HSP-causing genes including ENTPD1, CYP7B1, and ZFYVE26 were identified, respectively. Intra and interfamilial clinical variability were observed among affected individuals. Mutations in CYP7B1 and ZFYVE26 are relatively common causes of HSP and associated with SPG5A and SPG15, respectively. However, mutations in ENTPD1 are related to SPG64 which is an ultra-rare form of HSP. The research affirmed more complexities of phenotypic manifestations and allelic heterogeneity in HSP. Due to these complexities, it is not feasible to show a clear phenotype-genotype correlation in HSP cases. Identification of more families with mutations in HSP-causing genes may help the establishment of this correlation, further understanding of the molecular basis of the disease, and would provide an opportunity for genetic-counseling in these families.

Giant axonal neuropathy: The first Iranian case with a variation in the gigaxonin gene and a glance to the other cases.

Background: Giant axonal neuropathy (GAN) is a very rare fatal neurodegenerative disorder with clinical and allelic heterogeneity. The disease is caused by mutations in the GAN (gigaxonin) gene. Herein, we reported the clinical presentations and results of genetic analysis of the first Iranian GAN case. Methods: Phenotypic data were obtained by neurologic examination, brain magnetic resonance imaging (MRI), electromyography (EMG), electroencephalography (EEG), and sonography from the proband. Deoxyribonucleic acid (DNA) was isolated from peripheral blood leucocytes and whole exome sequencing (WES) was performed. The candidate variant was screened by Sanger sequencing in the proband and her family members. Results: The proband was a 7-year-old girl who was admitted with a chief complaint of ataxia, muscle weakness, delayed developmental milestones, and history of psychiatric disorders. She was very moody and had clumsy gait, decreased deep tendon reflexes (DTRs) of lower limbs, and kinky hair. The brain MRI revealed white matter abnormality. The EMG revealed that her disease was compatible with the chronic axonal type of sensorimotor polyneuropathy; however, her EEG was normal. Results of the WES revealed a homozygous variant; c.G778T:p.E260* in the GAN gene, indicating the GAN disorder. Conclusion: The present study affirmed GAN allelic heterogeneity and resulted in the expansion of the phenotypic spectrum of GAN pathogenic variants. Identification of more families with mutations in GAN gene helps to further understand the molecular basis of the disease and provides an opportunity for genetic counseling especially in the populations with a high degree of consanguineous marriage such as the Iranian population.