Lifetime risk of autosomal recessive neurodegeneration with brain iron accumulation (NBIA) disorders calculated from genetic databases.

BACKGROUND: Neurodegeneration with brain iron accumulation (NBIA) are a group of clinically and genetically heterogeneous diseases characterized by iron overload in basal ganglia and progressive neurodegeneration. Little is known about the epidemiology of NBIA disorders. In the absence of large-scale population-based studies, obtaining reliable epidemiological data requires innovative approaches. METHODS: All pathogenic variants were collected from the 13 genes associated with autosomal recessive NBIA (PLA2G6, PANK2, COASY, ATP13A2, CP, AP4M1, FA2H, CRAT, SCP2, C19orf12, DCAF17, GTPBP2, REPS1). The allele frequencies of these disease-causing variants were assessed in exome/genome collections: the Genome Aggregation Database (gnomAD) and our in-house database. Lifetime risks were calculated from the sum of allele frequencies in the respective genes under assumption of Hardy-Weinberg equilibrium. FINDINGS: The combined estimated lifetime risk of all 13 investigated NBIA disorders is 0.88 (95% confidence interval 0.70-1.10) per 100,000 based on the global gnomAD dataset (n = 282,912 alleles), 0.92 (0.65-1.29) per 100,000 in the European gnomAD dataset (n = 129,206), and 0.90 (0.48-1.62) per 100,000 in our in-house database (n = 44,324). Individually, the highest lifetime risks (>0.15 per 100,000) are found for disorders caused by variants in PLA2G6, PANK2 and COASY. INTERPRETATION: This population-genetic estimation on lifetime risks of recessive NBIA disorders reveals frequencies far exceeding previous population-based numbers. Importantly, our approach represents lifetime risks from conception, thus including prenatal deaths. Understanding the true lifetime risk of NBIA disorders is important in estimating disease burden, allocating resources and targeting specific interventions. FUNDING: This work was carried out in the framework of TIRCON ("Treat Iron-Related Childhood-Onset Neurodegeneration").

Neurodegeneration with brain iron accumulation: Characterization of clinical, radiological, and genetic features of pediatric patients from Southern India.

BACKGROUND: Neurodegeneration with brain iron accumulation (NBIA) is a group of rare inherited neurodegenerative disorders. Ten types of NBIA are known. Studies reporting various NBIA subtypes together are few. This study was aimed at describing clinical features, neuroimaging findings, and genetic mutations of different NBIA group disorders. METHODS: Clinical, radiological, and genetic data of patients diagnosed with NBIA in a tertiary care centre in Southern India from 2014 to 2020 was retrospectively collected and analysed. RESULTS: In our cohort of 27 cases, PLA2G6-associated neurodegeneration (PLAN) was most common (n = 13) followed by Pantothenate kinase-associated neurodegeneration (PKAN) (n = 9). We had 2 cases each of Mitochondrial membrane-associated neurodegeneration (MPAN) and Beta-propeller protein- associated neurodegeneration (BPAN) and 1 case of Kufor-Rakeb Syndrome (KRS). Walking difficulty was the presenting complaint in all PKAN cases, whereas the presentation in PLAN was that of development regression with onset at a mean age of 2 years. Overall, 50% patients of them presented with development regression and one-third had epilepsy. Presence of pyramidal signs was most common examination feature (89%) followed by one or more eye findings (81%) and movement disorders (50%). Neuroimaging was abnormal in 24/27 cases and cerebellar atrophy was the commonest finding (52%) followed by globus pallidus hypointensities (44%). CONCLUSIONS: One should have a high index of clinical suspicion for the diagnosis of NBIA in children presenting with neuroregression and vision abnormalities in presence of pyramidal signs or movement disorders. Neuroimaging and ophthalmological evaluation provide important clues to diagnosis in NBIA syndromes.

Analysis of ATP13A2 in large neurodegeneration with brain iron accumulation (NBIA) and dystonia-parkinsonism cohorts.

Several causative genes have been identified for both dystonia-parkinsonism and neurodegeneration with brain iron accumulation (NBIA), yet many patients do not have mutations in any of the known genes. Mutations in the ATP13A2 lead to Kufor Rakeb disease, a form of autosomal recessive juvenile parkinsonism that also features oromandibular dystonia. More recently, evidence of iron deposition in the caudate and putamen have been reported in patients with ATP13A2 mutations. We set out to determine the frequency of ATP13A2 mutations in cohorts of idiopathic NBIA and dystonia-parkinsonism. We screened for large deletions using whole genome arrays, and sequenced the entire coding region in 92 cases of NBIA and 76 cases of dystonia-parkinsonism. A number of coding and non-coding sequence variants were identified in a heterozygous state, but none were predicted to be pathogenic based on in silico analyses. Our results indicate that ATP13A2 mutations are a rare cause of both NBIA and dystonia-parkinsonism.

Phenotypic spectrum of neurodegeneration associated with mutations in the PLA2G6 gene (PLAN).

BACKGROUND: Neurodegeneration associated with brain iron accumulation (NBIA) comprises a heterogeneous group of disorders in which disruption of cellular mechanisms leads to accumulation of iron in the basal ganglia. This group includes patients with recently discovered mutations in the PLA2G6 gene encoding a calcium-independent phospholipase A2 enzyme that catalyzes the hydrolysis of glycerophospholipids. Previously, children with PLA2G6 mutations have been diagnosed with several different disorders and we wished to better define the phenotype of PLA2G6- associated neurodegeneration. METHODS: Detailed review of the clinical and genetic features of 14 and radiologic features of 13 of these patients with PLA2G6 mutations was undertaken. RESULTS: Median age of symptom presentation was 14 months. One third of the cohort presented following an intercurrent illness. The children had progressive cognitive and motor skill regression, with evidence of axial hypotonia, four limb spasticity, bulbar dysfunction, and strabismus. All patients developed cerebellar ataxia and dystonia. Most patients had optic atrophy. Brain imaging demonstrated cerebellar cortical atrophy and gliosis in all patients. Changes consistent with increased iron deposition were identified in the globus pallidus and substantia nigra. Novel corpus callosum changes are also reported. CONCLUSION: We describe a cohort of patients with PLA2G6-associated neurodegeneration (PLAN). Although patients with PLAN have previously been diagnosed with infantile neuroaxonal dystrophy, neurodegeneration associated with brain iron accumulation, and Karak syndrome, they display a characteristic clinical and radiologic phenotype. PLA2G6 mutational analysis will negate the need for more invasive diagnostic procedures such as tissue biopsy.