Small striatal huntingtin inclusions in patients with motor neuron disease with reduced penetrance and intermediate HTT gene expansions

Anna-Karin Roos; Erica Stenvall; Emmy Skelton Kockum; Kornelia Åman Grönlund; Helena Alstermark; Anna Wuolikainen; Peter M Andersen; Angelica Nordin; Karin M E Forsberg

doi:10.1093/hmg/ddae137

Small striatal huntingtin inclusions in patients with motor neuron disease with reduced penetrance and intermediate HTT gene expansions

Hum Mol Genet. 2024 Sep 13:ddae137. doi: 10.1093/hmg/ddae137. Online ahead of print.

Authors

Anna-Karin Roos¹, Erica Stenvall², Emmy Skelton Kockum², Kornelia Åman Grönlund¹, Helena Alstermark¹, Anna Wuolikainen³, Peter M Andersen¹, Angelica Nordin², Karin M E Forsberg¹

Affiliations

¹ Department of Clinical Sciences, Neurosciences, Umeå University, Norrlands University Hospital, Building 6 M, Floor 4, Umeå SE-90184, Sweden.
² Department of Medical Biosciences, Umeå University, Norrlands University Hospital, Building 6 M, Floor 2, Umeå SE-90184, Sweden.
³ Department of Medical Sciences, Neurology, Uppsala University, Uppsala University Hospital, Entrance 85, Floor 2, Uppsala SE-75185, Sweden.

PMID: 39270726
DOI: 10.1093/hmg/ddae137

Abstract

Short tandem repeat expansions in the human genome are overrepresented in a variety of neurological disorders. It was recently shown that huntingtin (HTT) repeat expansions with full penetrance, i.e. 40 or more CAG repeats, which normally cause Huntington's disease (HD), are overrepresented in patients with amyotrophic lateral sclerosis (ALS). Whether patients carrying HTT repeat expansions with reduced penetrance, (36-39 CAG repeats), or alleles with intermediate penetrance, (27-35 CAG repeats), have an increased risk of ALS has not yet been investigated. Here, we examined the role of HTT repeat expansions in a motor neuron disease (MND) cohort, searched for expanded HTT alleles, and investigated correlations with phenotype and neuropathology. MND patients harboring C9ORF72 hexanucleotide repeat expansions (HREs) were included, to investigate whether HTT repeat expansions were more common in this group. We found a high prevalence of intermediate (range 5.63%-6.61%) and reduced penetrance (range 0.57%-0.66%) HTT gene expansions in this cohort compared to other populations of European ancestry, but no differences between the MND cohort and the control cohort were observed, regardless of C9ORF72HRE status. Upon autopsy of three patients with intermediate or reduced penetrance HTT alleles, huntingtin inclusions were observed in the caudate nucleus and frontal lobe, but no significant somatic mosaicism was detected in different parts of the nervous system. Thus, we demonstrate, for the first time, huntingtin inclusions in individuals with MND and intermediate and reduced penetrance HTT repeat expansions but more clinicopathological investigations are needed to further understand the impact of HTT gene expansion-related pleiotropy.

Keywords: C9ORF72HRE; Amyotrophic lateral sclerosis; huntingtin inclusions; somatic mosaicism.

Abstract

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