Kooy, R. F. | bioRxiv Science

bioRxiv2024

C9orf72 expansion creates the unstable folate-sensitive fragile site FRA9A

The hyper-unstable Chr9p21 locus, harbouring the interferon gene cluster, oncogenes and C9orf72, is linked to multiple diseases. C9orf72 (GGGGCC)n expansions (C9orf72Exp) are associated with incompletely penetrant amyotrophic lateral sclerosis, frontotemporal dementia and autoimmune disorders. C9orf72Exp patients display hyperactive cGAS-STING-linked interferon immune and DNA damage responses, but the source of immuno-stimulatory or damaged DNA is unknown. Here, we show C9orf72Exp in pre-symptomatic and ALS-FTD patient cells and brains cause the folate- sensitive chromosomal fragile site, FRA9A. FRA9A centers on >33kb of C9orf72 as highly-compacted chromatin embedded in an 8.2Mb fragility zone spanning 9p21, encompassing 46 genes, making FRA9A one of the largest fragile sites. C9orf72Exp cells show chromosomal instability, heightened global- and Chr9p-enriched sister-chromatid exchanges, truncated-Chr9s, acentric-Chr9s and Chr9-containing micronuclei, providing endogenous sources of damaged and immunostimulatory DNA. Cells from one C9orf72Exp patient contained highly-rearranged FRA9A-expressing Chr9 with Chr9-wide dysregulated gene expression. Somatic C9orf72Exp repeat instability and chromosomal fragility are sensitive to folate-deficiency. Age-dependent repeat instability, chromosomal fragility, and chromosomal instability can be transferred to CNS and peripheral tissues of transgenic C9orf72Exp mice, implicating C9orf72Exp as the source. Our results highlight unappreciated effects of C9orf72 expansions that trigger vitamin-sensitive chromosome fragility, adding structural variations to the disease-enriched 9p21 locus, and likely elsewhere. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=94 SRC="FIGDIR/small/620312v2_ufig1.gif" ALT="Figure 1"> View larger version (31K): org.highwire.dtl.DTLVardef@154b23borg.highwire.dtl.DTLVardef@1814a6dorg.highwire.dtl.DTLVardef@13d713eorg.highwire.dtl.DTLVardef@d5d994_HPS_FORMAT_FIGEXP M_FIG C_FIG

genetics↗

bioRxiv2022

De Novo, Post-Zygotic, Inter-Tissue Mosaicism of Cell Autonomous ADNP Mutations in Autistic Individuals: Restricted Environmental Contribution

Many neurodevelopmental disorders, including autism, are caused by de novo mutations, that might arise as early as in the parental germline, during embryonic, fetal development, or as late as post-natal aging. Intra-tissue mutation-load variations could impact clinical presentation. One of the most common causes of autism is de novo mutations in ADNP. We developed an ultra-sensitive, highly-quantitative droplet digital PCR assay to determine ADNP mutation levels in patient tissues, including blood, teeth, hair, and 24 different tissues from a post-mortem de novo ADNP-mutated child ([~]6-years old), including a transplanted liver from a non-mutant donor (retained for 22 months). Striking variations of ADNP mosaicism arose between tissues of the same individual. Mutation load differences were evident between post-mortem tissues, but not in the transplanted liver -- supporting a cell autonomous genetic vulnerability to de novo mutations, arguing against a transferable environmentally-sensitive DNA damage/mutation predisposition. Variations between tissues suggest a developmental timing of the mutations. Most individuals showed at least one tissue with less than heterozygous mutations, where the presence of the homozygous non-mutant cells indicates that de novo ADNP mutations arose post-zygotically. Highly variable ADNP mosaicism between tissues, that within an individual can be less than heterozygous or approach homozygosity, indicate rapid ongoing post-zygotic, and possibly post-natal, somatic mutations, contributing to clinical variability.

genetics↗