No evidence of PGRN or MAPT gene dosage alterations in a collection of patients with frontotemporal lobar degeneration

A comprehensive screening of copy number variability in dementia with Lewy bodies

The role of genetic variability in dementia with Lewy bodies (DLB) is now indisputable; however, data regarding copy number variation (CNV) in this disease has been lacking. Here, we used whole-genome genotyping of 1454 DLB cases and 1525 controls to assess copy number variability. We used 2 algorithms to confidently detect CNVs, performed a case-control association analysis, screened for candidate CNVs previously associated with DLB-related diseases, and performed a candidate gene approach to fully explore the data. We identified 5 CNV regions with a significant genome-wide association to DLB; 2 of these were only present in cases and absent from publicly available databases: one of the regions overlapped LAPTM4B, a known lysosomal protein, whereas the other overlapped the NME1 locus and SPAG9. We also identified DLB cases presenting rare CNVs in genes previously associated with DLB or related neurodegenerative diseases, such as SNCA, APP, and MAPT. To our knowledge, this is the first study reporting genome-wide CNVs in a large DLB cohort. These results provide preliminary evidence for the contribution of CNVs in DLB risk.

Plasma progranulin levels in cortical dementia phenotypes with asymmetric perisylvian atrophy

BACKGROUND AND PURPOSE

Decreased plasma progranulin levels are a very specific marker for the diagnosis of frontotemporal lobar degeneration (FTLD) caused by mutations in the progranulin gene (GRN). A frequent neuroimaging pattern in this type of dementia is asymmetric cortical atrophy. The aim of this study was to screen for GRN-linked FTLD in cases with different cortical dementia phenotypes and asymmetric perisylvian atrophy.

METHODS

Progranulin plasma levels were analyzed in a variety of FTLD phenotypes (n = 71), dementia of the Alzheimer type (DAT) (n = 22) and probable Lewy body dementia (n = 8), both latter groups presented with asymmetric perisylvian atrophy. A group of elderly controls (n = 29) and DAT cases with symmetric atrophy (n = 33) were also analyzed. The GRN gene was sequenced in cases with lower plasma levels.

RESULTS

Four cases with clinical FTLD phenotypes and plasma levels below 70 ng/ml were found to carry different GRN mutations: M1?, C139R, a point mutation in the splice donor site of intron 3 (A89VfsX41), and a deletion in exon 9 (A303AfsX57), this latter one being a new mutation. Thirteen cases with levels between 72 and 85 ng/ml did not show pathogenic changes in the GRN gene. None of the cases with asymmetric atrophy and clinical phenotypes other than FTLD had GRN mutations.

CONCLUSIONS

Asymmetric perisylvian atrophy is not likely to predict progranulin-linked FTLD unless it is associated with a consistent FTLD clinical phenotype.

De novo triplication of the MAPT gene from the recurrent 17q21.31 microdeletion region in a patient with moderate intellectual disability and various minor anomalies

We report on a 16-year-old male patient with moderate intellectual disability, behavioral problems, and further anomalies such as facial dysmorphism, heart defect, and urogenital anomalies. By molecular karyotyping we identified the first de novo copy number gain to four copies on chromosome 17q21.31 including the MAPT gene but not the entire recurrent microdeletion/microduplication region. Recurrent microdeletions of this region including the MAPT and the CHRH1 genes have been shown to be a relatively frequent cause of intellectual disability, while only a few reciprocal duplications in patients with variable cognitive disorders have been published so far. A common inversion polymorphism in this region has been linked to a distinct H2 haplotype and seems to be associated with an increased risk for microdeletions and -duplications. Our patient and his father were both heterozygous for the H1/H2 haplotype, whereas the mother was homozygous for the H2 haplotype. In our patient the dosage gain apparently occurred on the paternal H1 allele and did not involve the H2 allele as in the previously published cases. This patient further delineates the genotypic and phenotypic variability associated with copy number variants from the 17q21.31 microdeletion region.

Frontotemporal dementia: from Mendelian genetics towards genome wide association studies

Frontotemporal lobar degeneration is the most common cause of dementia of non-Alzheimer's type worldwide. It manifests, clinically, with behavioural changes and language impairment and is pathologically associated with tau- or ubiquitin-positive inclusions detected in neurons and glial cells of the frontal and temporal lobes in the brain. Genetic variations in the microtubule-associated protein tau and progranulin genes explain almost 50% of familial cases, whilst variations in TAR DNA-binding protein, charged multivescicular body protein 2B, valosin-containing protein and fused in sarcoma genes contribute to <5% of cases. The rapidly developing investigative techniques available to geneticists such as genome-wide association studies, whole-exome sequencing and, soon, whole-genome sequencing promise to contribute to the unravelling of the genetic architecture of this complex disease and, in the future, to the development of more sensitive, accurate and effective diagnostic and treatment measures.