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

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.

Amyotrophic Lateral Sclerosis

“…If a mutation has not been previously identified in an affected family member, the application and interpretation of genetic testing in a healthy, at-risk individual can be difficult, if not impossible. For those with a family history consistent with autosomal dominant inheritance, but no identified family gene mutation, at-risk individuals may still benefit from counseling to address life and financial planning concerns, as well as ongoing psychosocial and educational support regarding their possible lifetime risk for ALS [49].…”

“…Many neurodegenerative conditions, including ALS, follow the guidelines developed in the Huntington disease community for the provision of predictive genetic testing services [49][50][51]. The predictive counseling model includes two genetic counseling sessions prior to testing, as well as consultations with a neurologist, psychologist, and/or neuropsychologist, and an in-person disclosure of the result accompanied by a support person.…”

Genetic counselling in ALS: facts, uncertainties and clinical suggestions

“…The whole family may experience emotional, psychological, ethical and legal implications 17. Psychological effects involve uncertainties about the predictivity of genetic testing, sometimes uninformative, for the positive subject, concerns about relatives and different attitudes toward sharing genetic information with family members.…”

“…The information leaflet should include the following: (1) information about ALS, (2) the purpose, nature and consequences of the genetic testing, (3) risks involved in the procedure, (4) limitations of test interpretation (eg, other not yet identified Mendelian genes, genetic mutations that predispose to ALS), in particular regarding C9ORF72 ,17 (5) practical information on what will happen next, (6) potential harm of test, (7) potential psychosocial, ethical and legal ramifications, (8) implications for family members, (9) available resources, including those offered by the ALS centre and (10) information on lay associations and support groups. The information leaflet should be periodically revised to reflect all significant scientific and clinical advances.…”

C9orf72-related disorders: expanding the clinical and genetic spectrum of neurodegenerative diseases

“…Semantic dementia and progressive non-fluent aphasia have rarely been described in association with motor neuron signs 9 , but might not exclude the hypothesis of C9orf72 gene hexanucleotide repeat expansion 13 . Neuropsychiatric profile involves early disinhibition (up to 85%), lack of insight (up to 78%), hallucinations (up to 50%), delusion (up to 50%), anxiety (up to 52%), hyperorality (up to 100%), early apathy (up to 100%), loss of empathy (up to 77%) and obsessive-compulsive symptoms (up to 12%) 5,42,43 . There is an important clinical overlap with probable Alzheimer's disease in the early-onset cases, mainly in Caucasian patients 45,46 , making it difficult to promote a proper genetic evaluation in association with classical genes (APP, PSEN1, PSEN2) 47,48 , although such cases generally present with an older age than with the FTD clinical spectrum 26 .…”