Pedigree with frontotemporal lobar degeneration--motor neuron disease and Tar DNA binding protein-43 positive neuropathology: genetic linkage to chromosome 9

Abstract

Background: Frontotemporal lobar degeneration (FTLD) represents a clinically, pathologically and genetically heterogenous neurodegenerative disorder, often complicated by neurological signs such as motor neuron-related limb weakness, spasticity and paralysis, parkinsonism and gait disturbances. Linkage to chromosome 9p had been reported for pedigrees with the neurodegenerative disorder, frontotemporal lobar degeneration (FTLD) and motor neuron disease (MND). The objective in this study is to identify the genetic locus in a multi-generational Australian family with FTLD-MND.

Methods: Clinical review and standard neuropathological analysis of brain sections from affected pedigree members. Genome-wide scan using microsatellite markers and single nucleotide polymorphism fine mapping. Examination of candidate genes by direct DNA sequencing.

Results: Neuropathological examination revealed cytoplasmic deposition of the TDP-43 protein in three affected individuals. Moreover, we identify a family member with clinical Alzheimer's disease, and FTLD-Ubiquitin neuropathology. Genetic linkage and haplotype analyses, defined a critical region between markers D9S169 and D9S1845 on chromosome 9p21. Screening of all candidate genes within this region did not reveal any novel genetic alterations that co-segregate with disease haplotype, suggesting that one individual carrying a meiotic recombination may represent a phenocopy. Re-analysis of linkage data using the new affection status revealed a maximal two-point LOD score of 3.24 and a multipoint LOD score of 3.41 at marker D9S1817. This provides the highest reported LOD scores from a single FTLD-MND pedigree.

Conclusion: Our reported increase in the minimal disease region should inform other researchers that the chromosome 9 locus may be more telomeric than predicted by published recombination boundaries. Moreover, the existence of a family member with clinical Alzheimer's disease, and who shares the disease haplotype, highlights the possibility that late-onset AD patients in the other linked pedigrees may be mis-classified as sporadic dementia cases.

Figure 1

Pedigree diagram showing affection status and disease haplotype. Squares indicate males and circles females; filled arrow indicates proband; black symbols show individuals clinically diagnosed with dementia, either AD or FTLD; diagonal stripes, individuals diagnosed with MND; and combined black and diagonal stripes, individuals diagnosed with FTLD-MND. A diagonal line marks deceased subjects. Individual I:1, lived until his 80s, but was thought to have had some personality changes. Alleles in parentheses are inferred. 'X' indicates upper and lower recombination breakpoints that define the minimal disease haplotype.

Figure 2

The neuropathology of patients III:2 and III:3. (A) Severe pyramidal neuronal loss from CA1 region Ammon's horn (III:2). (B) Temporal neocortex showing Aβ immunopositive plaques and cerebrovascular amyloidosis (III:2). Positive staining with ubiquitin (C-F) and TDP-43 (G-I) antibodies of neuronal cytoplasmic inclusions (NCI) in the granule cells of the dentate gyrus. Ubiquitin-positive neuronal cytoplasmic inclusions in III:2 (C, E and F) and in III:3 (D). TDP-43 positive neuronal cytoplasmic inclusions in III:2 (G and I) and III:3 (H). Bar = 50 μm in A and B; 20 μm in C and G; 10 μm in D, E, F, H and I.

Figure 3

The neuropathology of case III:12. (A) C7 cervical cord showing symmetrical Wallerian degeneration of lateral corticospinal tracts and anterior corticospinal tract. Note atrophy of anterior nerve roots in comparison to dorsal nerve roots. TDP-43 immunopositive skein-like (B) and punctate (C) cytoplasmic inclusions within anterior horn cells of the spinal cord. (D) Normal TDP-43 positive nuclear staining of the anterior horn cell. (E) Anterior horn cell showing Bunina bodies. (F) Spongiosis in layers 2 and 3 of parasagittal motor cortex. (G) Residual Betz cell in motor cortex. Bar = 10 μm in B, C, D, E and G; 20 μm in F.

Figure 4

Fine mapping haplotype analysis using microsatellite and SNP markers to resolve the position of a meiotic recombination in pedigree member III:8. Four SNPs from representative genes are indicated (rs10812616, rs10812615, rs17769294 and rs10122902 for C9orf11; rs2383768, rs13296489, rs1331870 and rs10968460 for LINGO2; rs2026739, rs3780473, rs10970975 and rs12985 for ACO1; rs10813831, Arg71His, rs17289927 and rs6476363 for DDX8). The informative SNP haplotypes definitively place the recombination breakpoint between D9S1118 and D9S304. The black box indicates the portion of the disease haplotype which is not shared by pedigree member III:8. Transcript map indicating the relative positions of known genes and transcripts (open boxes) (not drawn to scale).

Figure 5

Diagram of chromosome 9p-linked families with FTLD-MND.