Intracranial calcifications and dystonia associated with a novel deletion of chromosome 8p11.2 encompassing SLC20A2 and THAP1

Unveiling distinct clinical manifestations of primary familial brain calcifications in Asian and European patients: A study based on 10-year individual-level data

BACKGROUND

Primary Familial Brain Calcification (PFBC) can manifest clinically with a complex and heterogeneous array of symptoms, including parkinsonism, dysarthria, and cognitive impairment. However, the distinct presentations of PFBC in Asian and European populations remain unclear.

METHODS

We conducted a systematic search of PubMed for studies involving genetically confirmed PFBC patients. Demographic data, genetic information, radiological examinations, and clinical characteristics were extracted for each case.

RESULTS

The study included 120 publications and 564 genetically confirmed PFBC patients. Asian and European PFBC populations represented 54 % and 37 % of global patients, respectively. While calcification patterns showed no significant differences between Asian and European PFBC patients, European autosomal dominant PFBC variant carriers were more likely to exhibit clinical symptoms compared to their Asian counterparts (OR = 2.90, 95 % CI 1.55-5.60) and had an earlier estimated age of onset (median age 42 vs 58).

CONCLUSION

The interaction between regional differences and genetically determined calcification severity may collectively influence PFBC symptom progression. Future research should further explore the potential roles of gene modifiers, ethnic background, socioeconomic and environmental exposure factors underlying regional differences in PFBC progression.

The genetic landscape of basal ganglia and implications for common brain disorders

The basal ganglia are subcortical brain structures involved in motor control, cognition, and emotion regulation. We conducted univariate and multivariate genome-wide association analyses (GWAS) to explore the genetic architecture of basal ganglia volumes using brain scans obtained from 34,794 Europeans with replication in 4,808 white and generalization in 5,220 non-white Europeans. Our multivariate GWAS identified 72 genetic loci associated with basal ganglia volumes with a replication rate of 55.6% at P < 0.05 and 87.5% showed the same direction, revealing a distributed genetic architecture across basal ganglia structures. Of these, 50 loci were novel, including exonic regions of APOE, NBR1 and HLAA. We examined the genetic overlap between basal ganglia volumes and several neurological and psychiatric disorders. The strongest genetic overlap was between basal ganglia and Parkinson's disease, as supported by robust LD-score regression-based genetic correlations. Mendelian randomization indicated genetic liability to larger striatal volume as potentially causal for Parkinson's disease, in addition to a suggestive causal effect of greater genetic liability to Alzheimer's disease on smaller accumbens. Functional analyses implicated neurogenesis, neuron differentiation and development in basal ganglia volumes. These results enhance our understanding of the genetic architecture and molecular associations of basal ganglia structure and their role in brain disorders.

Brain Calcifications: Genetic, Molecular, and Clinical Aspects

Many conditions can present with accumulation of calcium in the brain and manifest with a variety of neurological symptoms. Brain calcifications can be primary (idiopathic or genetic) or secondary to various pathological conditions (e.g., calcium-phosphate metabolism derangement, autoimmune disorders and infections, among others). A set of causative genes associated with primary familial brain calcification (PFBC) has now been identified, and include genes such as SLC20A2, PDGFB, PDGFRB, XPR1, MYORG, and JAM2. However, many more genes are known to be linked with complex syndromes characterized by brain calcifications and additional neurologic and systemic manifestations. Of note, many of these genes encode for proteins involved in cerebrovascular and blood-brain barrier functions, which both represent key anatomical structures related to these pathological phenomena. As a growing number of genes associated with brain calcifications is identified, pathways involved in these conditions are beginning to be understood. Our comprehensive review of the genetic, molecular, and clinical aspects of brain calcifications offers a framework for clinicians and researchers in the field.

Novel 12 Mb interstitial deletion of chromosome 8p11.22-p21.2: a case report

Background

The deletion of a short arm fragment on chromosome 8 is a rare cause of Kallmann syndrome and spherocytosis due to deletion of the FGFR1 and ANK1 genes.

Case presentation

This case study describes a 4-month-old child with growth and psychomotor retardation, auricle deformity, microcephaly, polydactyly, a heart abnormality, and feeding difficulties. An approximately 12.00 MB deletion was detected in the 8p11.22-p21.2 region of chromosome 8. After sequencing, we found that 65 protein genes had been deleted, including FGFR1, which resulted in Kallmann syndrome. There was no deletion of the ANK1 gene associated with spherocytosis, consistent with the phenotype.

Conclusion

This patient is a new case of short arm deletion of chromosome 8, resulting in novel and previously unreported clinical features.

Case Report: Two Novel Frameshift Mutations in SLC20A2 and One Novel Splice Donor Mutation in PDGFB Associated With Primary Familial Brain Calcification

Primary familial brain calcification (PFBC, OMIM#213600), also known as Fahr's disease, is characterized by bilateral and symmetric brain calcification in the basal ganglia (globus pallidus, caudate nucleus, and putamen), thalamus, subcortical white matter, and cerebellum. PFBC can be caused by loss-of-function mutations in any of the six known causative genes. The most common clinical manifestations include movement disorders, cognitive impairment, and neuropsychiatric signs that gradually emerge in middle-aged patients. To broaden the PFBC mutation spectrum, we examined nine members of a family with PFBC and two sporadic cases from clinical departments, and sequenced all PFBC-causative genes in the index case. Two novel frameshift mutations in SLC20A2 [NM_001257180.2; c.806delC, p.(Pro269Glnfs^*49) and c.1154delG, p.(Ser385Ilefs^*70)] and one novel splice donor site mutation (NM_002608.4, c.456+1G>C, r.436_456del) in PDGFB were identified in the patient cohort. c.806delC co-segregated with brain calcification and led to SLC20A2 haploinsufficiency among the affected family members. The c.456+1G>C mutation in PDGFB resulted in aberrant mRNA splicing, thereby forming mature transcripts containing an in-frame 21 base pair (bp) deletion, which might create a stably truncated protein [p.(Val146_Gln152del)] and exert a dominant negative effect on wild-type PDGFB. All three mutations were located in highly conserved regions among multiple species and predicted to be pathogenic, as evaluated by at least eight common genetic variation scoring systems. This study identified three novel mutations in SLC20A2 and PDGFB, which broadened and enriched the PFBC mutation spectrum.

Isolated dystonia: clinical and genetic updates

Four genes associated with isolated dystonia are currently well replicated and validated. DYT-THAP1 manifests as young-onset generalized dystonia with predominant craniocervical symptoms; and is associated with mostly deleterious missense variation in the THAP1 gene. De novo and inherited missense and protein truncating variation in GNAL as well as primarily missense variation in ANO3 cause isolated focal and/or segmental dystonia with preference for the upper half of the body and older ages at onset. The GAG deletion in TOR1A is associated with generalized dystonia with onset in childhood in the lower limbs. Rare variation in these genes causes monogenic sporadic and inherited forms of isolated dystonia; common variation may confer risk and imply that dystonia is a polygenic trait in a subset of cases. Although candidate gene screens have been successful in the past in detecting gene-disease associations, recent application of whole-genome and whole-exome sequencing methods enable unbiased capture of all genetic variation that may explain the phenotype. However, careful variant-level evaluation is necessary in every case, even in genes that have previously been associated with disease. We review the genetic architecture and phenotype of DYT-THAP1, DYT-GNAL, DYT-ANO3, and DYT-TOR1A by collecting case reports from the literature and performing variant classification using pathogenicity criteria.

Global retardation and hereditary spherocytosis associated with a novel deletion of chromosome 8p11.21 encompassing KAT6A and ANK1

The loss of heterozygosity localized at chromosome segment 8p11.2 causes a contiguous gene syndrome, which mostly combined phenotype of Kallmann syndrome and hereditary spherocytosis. It has been documented that this combined phenotype is in association with both the deletion of the fibroblast growth factor receptor 1 (FGFR1) and ankyrin 1 (ANK1) genes. Here, we described a 6-year-old girl with microcephaly, global developmental delay, mental retardation, and hereditary spherocytosis, associated with a heterozygous pathogenic microdeletion of 1.9 Mb size at 8p11.21. Molecular analysis confirmed that the identified microdeletion contained two OMIM (Online Mendelian Inheritance in Man)genes, including ANK1 and lysine acetyltransferase 6 A (KAT6A), but not FGFR1. Therefore, the simultaneous occurrence of mild developmental delay and distinctive facial in this patient was associated with the pathogenic variation of the KAT6A.

Basal ganglia calcifications (Fahr's syndrome): related conditions and clinical features

Basal ganglia calcifications could be incidental findings up to 20% of asymptomatic patients undergoing CT or MRI scan. The presence of neuropsychiatric symptoms associated with bilateral basal ganglia calcifications (which could occur in other peculiar brain structures, such as dentate nuclei) identifies a clinical picture defined as Fahr's Disease. This denomination mainly refers to idiopathic forms in which no metabolic or other underlying causes are identified. Recently, mutations in four different genes (SLC20A2, PDGFRB, PDGFB, and XPR1) were identified, together with novel mutations in the Myogenic Regulating Glycosylase gene, causing the occurrence of movement disorders, cognitive decline, and psychiatric symptoms. On the other hand, secondary forms, also identified as Fahr's syndrome, have been associated with different conditions: endocrine abnormalities of PTH, such as hypoparathyroidism, other genetically determined conditions, brain infections, or toxic exposure. The underlying pathophysiology seems to be related to an abnormal calcium/phosphorus homeostasis and transportation and alteration of the blood-brain barrier.