ABSTRACT
PLA2G6 gene associated neurodegenerative disorders resulting from homozygous c. 2222G > A (p.Arg741Gln) mutation were detected in two cases having variable neuropsychiatric phenotypic and imaging findings. Exome analysis helped identification of rare alleles, reinforcing ethnographic antecedents to geographical clustering of rare mutations and, essential to understanding biology of neurodegenerative disorders.
Subject(s)
Group VI Phospholipases A2/genetics , Heredodegenerative Disorders, Nervous System/genetics , White People/genetics , Alleles , Biological Variation, Population , Female , Heredodegenerative Disorders, Nervous System/ethnology , Homozygote , Humans , India , Male , Medical Illustration , Mutation , Phenotype , Exome Sequencing , Young AdultABSTRACT
Huntington disease (HD) is a progressive autosomal dominant neurodegenerative disorder, characterized by abnormal movements, cognitive decline, and psychiatric symptoms, caused by a CAG repeat expansion in the huntingtin (HTT) gene on chromosome 4p. A CAG/CTG repeat expansion in the junctophilin-3 (JPH3) gene on chromosome 16q24.2 causes a Huntington disease-like phenotype (HDL2). All patients to date with HDL2 have some African ancestry. The present study aimed to characterize the genetic basis of the Huntington disease phenotype in South Africans and to investigate the possible origin of the JPH3 mutation. In a sample of unrelated South African individuals referred for diagnostic HD testing, 62% (106/171) of white patients compared to only 36% (47/130) of black patients had an expansion in HTT. However, 15% (20/130) of black South African patients and no white patients (0/171) had an expansion in JPH3, confirming the diagnosis of Huntington disease like 2 (HDL2). Individuals with HDL2 share many clinical features with individuals with HD and are clinically indistinguishable in many cases, although the average age of onset and diagnosis in HDL2 is 5 years later than HD and individual clinical features may be more prominent. HDL2 mutations contribute significantly to the HD phenotype in South Africans with African ancestry. JPH3 haplotype studies in 31 families, mainly from South Africa and North America, provide evidence for a founder mutation and support a common African origin for all HDL2 patients. Molecular testing in individuals with an HD phenotype and African ancestry should include testing routinely for JPH3 mutations.
Subject(s)
Chorea/genetics , Dementia/genetics , Heredodegenerative Disorders, Nervous System/genetics , Membrane Proteins/genetics , Adult , Black People/genetics , Chorea/ethnology , Chorea/pathology , Cognition Disorders/ethnology , Cognition Disorders/genetics , Cognition Disorders/pathology , Dementia/ethnology , Dementia/pathology , Female , Genetic Association Studies , Haplotypes , Heredodegenerative Disorders, Nervous System/ethnology , Heredodegenerative Disorders, Nervous System/pathology , Humans , Huntington Disease/ethnology , Huntington Disease/genetics , Huntington Disease/pathology , Male , Microsatellite Repeats , Middle Aged , Mutation , Polymorphism, Single Nucleotide , South Africa , Trinucleotide Repeats , White People/geneticsABSTRACT
INTRODUCTION: SPOAN (spastic paraplegia, optic atrophy, and neuropathy) syndrome is an autosomal recessive neurodegenerative disorder identified in a large consanguineous Brazilian family. METHODS: Twenty-seven patients with SPOAN syndrome (20 women), aged 4-58 years, underwent nerve conduction studies (NCS) of the median, ulnar, tibial, and fibular nerves, and sensory NCS of the median, ulnar, radial, sural, and superficial fibular nerves. RESULTS: Sensory nerve action potentials were absent in the lower limbs and absent in >80% of upper limbs. Motor NCS had reduced amplitudes and borderline velocities in the upper limbs and absent compound muscle action potentials (CMAPs) in the lower limbs. CONCLUSIONS: The neuropathy in SPOAN syndrome is a severe, early-onset sensory-motor axonal polyneuropathy. Normal NCS seem to rule-out this condition.
