7 research outputs found
NPHP4 Variants Are Associated With Pleiotropic Heart Malformations
Rationale: Congenital heart malformations are a major cause of morbidity and mortality, especially in young children. Failure to establish normal left-right (L-R) asymmetry often results in cardiovascular malformations and other laterality defects of visceral organs. Objective: To identify genetic mutations causing cardiac laterality defects. Methods and Results: We performed a genome-wide linkage analysis in patients with cardiac laterality defects from a consanguineous family. The patients had combinations of defects that included dextrocardia, transposition of great arteries, double-outlet right ventricle, atrioventricular septal defects, and caval vein abnormalities. Sequencing of positional candidate genes identified mutations in NPHP4. We performed mutation analysis of NPHP4 in 146 unrelated patients with similar cardiac laterality defects. Forty-one percent of these patients also had laterality defects of the abdominal organs. We identified 8 additional missense variants that were absent or very rare in control subjects. To study the role of nphp4 in establishing L-R asymmetry, we used antisense morpholinos to knockdown nphp4 expression in zebrafish. Depletion of nphp4 disrupted L-R patterning as well as cardiac and gut laterality. Cardiac laterality defects were partially rescued by human NPHP4 mRNA, whereas mutant NPHP4 containing genetic variants found in patients failed to rescue. We show that nphp4 is involved in the formation of motile cilia in Kupffer's vesicle, which generate asymmetrical fluid flow necessary for normal L-R asymmetry. Conclusions: NPHP4 mutations are associated with cardiac laterality defects and heterotaxy. In zebrafish, nphp4 is essential for the development and function of Kupffer's vesicle cilia and is required for global L-R patterning
Astroglial-targeted expression of the fragile X CGG repeat premutation in mice yields RAN translation, motor deficits and possible evidence for cell-to-cell propagation of FXTAS pathology
The fragile X premutation is a CGG trinucleotide repeat expansion between 55 and 200 repeats in the 5′-
untranslated region of the fragile X mental retardation 1 (FMR1) gene. Human carriers of the premutation
allele are at risk of developing the late-onset neurodegenerative disorder, fragile X-associated tremor/ataxia
syndrome (FXTAS). Characteristic neuropathology associated with FXTAS includes intranuclear inclusions in
neurons and astroglia. Previous studies recapitulated these histopathological features in neurons in a knock-in
mouse model, but without significant astroglial pathology. To determine the role of astroglia in FXTAS, we
generated a transgenic mouse line (Gfa2-CGG99-eGFP) that selectively expresses a 99-CGG repeat expansion
linked to an enhanced green fluorescent protein (eGFP) reporter in astroglia throughout the brain, including
cerebellar Bergmann glia. Behaviorally these mice displayed impaired motor performance on the ladder-rung
test, but paradoxically better performance on the rotarod. Immunocytochemical analysis revealed that CGG99-
eGFP co-localized with GFAP and S-100ß, but not with NeuN, Iba1, or MBP, indicating that CGG99-eGFP
expression is specific to astroglia. Ubiquitin-positive intranuclear inclusions were found in eGFP-expressing glia
throughout the brain. In addition, intracytoplasmic ubiquitin-positive inclusions were found outside the nucleus in
distal astrocyte processes. Intriguingly, intranuclear inclusions, in the absence of eGFP mRNA and eGFP fluorescence,
were present in neurons of the hypothalamus and neocortex. Furthermore, intranuclear inclusions in both neurons and
astrocytes displayed immunofluorescent labeling for the polyglycine peptide FMRpolyG, implicating FMRpolyG in the
pathology found in Gfa2-CGG99 mice. Considered together, these results show that Gfa2-CGG99 expression in mice is
sufficient to induce key features of FXTAS pathology, including formation of intranuclear inclusions, translation of
FMRpolyG, and deficits in motor function
A missense variant in the nuclear export signal of the FMR1 gene causes intellectual disability
Fragile X syndrome (FXS) is the most common monogenetic cause of intellectual disability and autism spectrum disorders. Mostly, FXS is caused by transcriptional silencing of the FMR1 gene due to a repeat expansion in the 5' UTR, and consequently lack of the protein product FMRP. However, in rare cases FXS is caused by other types of variants in the FMR1 gene.We describe a missense variant in the FMR1 gene, identified through whole-exome sequencing, in a boy with intellectual disability and behavioral problems. The variant is located in the FMRP's nuclear export signal (NES). We performed expression and localization studies of the variant in hair roots and HEK293 cells. Our results show normal expression but significant retention of the FMRP in the cells' nucleus. This finding suggests a possible FMRP reduction at its essential functional sites in the dendrites and the synaptic compartments and possible interference of other cellular processes in the nucleus. Together, this might lead to a FXS phenotype in the boy.Genetics of disease, diagnosis and treatmen
Hereditary Pick's disease with the G272V tau mutation shows predominant three-repeat tau pathology
Frontotemporal dementia and parkinsonism linked to chromosome 17 have been associated with mutations in the microtubule associated protein tau (MAPT or tau) gene. This disorder is characterized by a large spectrum of neuronal and glial tau lesions in different brain regions. Pick bodies were found in a family with hereditary Pick's disease with the G272V mutation and in several families with other tau mutations in exons 9 and 11-13. The biochemical composition of Pick bodies varies between these mutations. Until recently, no detailed biochemical characterization of G272V brain material was done owing to unavailability of fresh frozen brain material. We now report a detailed study using the immunohistochemistry, western blots and electron microscopy of two brains with the G272V mutation that recently became available. Both brains showed severe neuronal loss in the temporal cortex, whereas in the frontal cortex the loss was less; and abundant Pick bodies in the dentate gyrus of the hippocampus, and caudate nucleus. The Pick bodies consisted exclusively of three-repeat (3R) isoforms, as was demonstrated by isoform-specific antibodies and supported by western blot analysis of sarkosyl-insoluble tau. These observations confirm that this family diagnosed with hereditary Pick disease meets all the criteria for this condition, including the presence of Pick bodies that are unphosphorylated at Se
PRKAR1B mutation associated with a new neurodegenerative disorder with unique pathology
Genetics of disease, diagnosis and treatmen
Elevated Fmr1 mRNA levels and reduced protein expression in a mouse model with an unmethylated Fragile X full mutation
The human FMR1 gene contains a CGG repeat in its 5′ untranslated region. The repeat length
in the normal population is polymorphic (5–55 CGG repeats). Lengths beyond 200 CGGs (full
mutation) result in the absence of the FMR1 gene product, FMRP, through abnormal
methylation and gene silencing. This causes Fragile X syndrome, the most common
inherited form of mental retardation. Elderly carriers of the premutation, defined as a repeat
length between 55 and 200 CGGs, can develop a progressive neurodegenerative syndrome:
Fragile X-associated tremor/ataxia syndrome (FXTAS). In FXTAS, FMR1 mRNA levels are
elevated and it has been hypothesised that FXTAS is caused by a pathogenic RNA gain-offunction
mechanism. We have developed a knock in mouse model carrying an expanded
CGG repeat (98 repeats), which shows repeat instability and displays biochemical,
phenotypic and neuropathological characteristics of FXTAS. Here, we report further
repeat instability, up to 230 CGGs. An expansion bias was observed, with the largest
expansion being 43 CGG units and the largest contraction 80 CGG repeats. In humans, this
length would be considered a full mutation and would be expected to result in gene
silencing. Mice carrying long repeats (∼230 CGGs) display elevated mRNA levels and
decreased FMRP levels, but absence of abnormal methylation, suggesting that modelling the
Fragile X full mutation in mice requires additional repeats or other genetic manipulation