Genetic counseling for FTD/ALS caused by the C9ORF72 hexanucleotide expansion

Jamie C Fong,Jill S Goldman,Anna M Karydas

doi:10.1186/alzrt130

Abstract

Frontotemporal degeneration (FTD) and amyotrophic lateral sclerosis (ALS) are related but distinct neurodegenerative diseases. The identification of a hexanucleotide repeat expansion in a noncoding region of the chromosome 9 open reading frame 72 (C9ORF72) gene as a common cause of FTD/ALS, familial FTD, and familial ALS marks the culmination of many years of investigation. This confirms the linkage of disease to chromosome 9 in large, multigenerational families with FTD and ALS, and it promotes deeper understanding of the diseases' shared molecular FTLD-TDP pathology. The discovery of the C9ORF72 repeat expansion has significant implications not only for familial FTD and ALS, but also for sporadic disease. Clinical and pathological correlates of the repeat expansion are being reported but remain to be refined, and a genetic test to detect the expansion has only recently become clinically available. Consequently, individuals and their families who are considering genetic testing for the C9ORF72 expansion should receive genetic counseling to discuss the risks, benefits, and limitations of testing. The following review aims to describe genetic counseling considerations for individuals at risk for a C9ORF72 repeat expansion.

Highlights

Frontotemporal degeneration (FTD) is a common cause of presenile dementia, affecting 15 to 20 per 100,000 individuals between ages 45 and 64 years [1]
The discovery of the chromosome 9 open reading frame 72 (C9ORF72) expansion marks a milestone in the long search for the underlying cause of chromosome 9-linked FTD and amyotrophic lateral sclerosis (ALS)
Additional studies will surely elucidate the molecular mechanisms that lead to C9ORF72-related neurodegeneration

Summary

Introduction

Frontotemporal degeneration (FTD) is a common cause of presenile dementia, affecting 15 to 20 per 100,000 individuals between ages 45 and 64 years [1]. Better correlation of clinical patterns to exact repeat size is needed before claims of decreasing age of onset and increasing severity of symptoms are associated with larger numbers of repeats across successive generations This scenario may create uncertainty for expansion-positive families with at-risk individuals considering genetic testing. ALS, amyotrophic lateral sclerosis; C9ORF72, chromosome 9 open reading frame 72; FTD, frontotemporal degeneration Another potential risk that should be discussed during genetic counseling for predictive testing involves genetic privacy. The patient’s son was counseled about the possibility of a C9ORF72 mutation in his family, and he understood the benefits, risks, and limitations of genetic testing. Genetic counseling encouraged the son to consider how best to help his father view diagnostic testing as a means to identify risk for family members, while maintaining sensitivity about his father’s perspective. The result was clinically confirmed but awaits disclosure, because the family remains undecided about whether or not to learn the information

Conclusion

51. Genetic Testing for Huntington’s Disease

55. Wertz DC

Findings

60. Kessler S