The genetics of motor neuron disease in New Zealand

Motor neuron disease (MND) is a group of adult-onset neurodegenerative diseases characterised by progressive motor neuron degeneration, of which amyotrophic lateral sclerosis (ALS) is the most common. MND is clinically heterogeneous with complex etiology, caused by or associated with over 40 different genes and multiple environmental risk factors. New Zealand has one of the highest global incidence and mortality rates of MND, however the reasons are unknown. We sought to identify the frequencies of genetic variants in known MND-linked genes among people with MND in New Zealand. We enrolled 184 participants: 149 with a clinical diagnosis of MND (128 sporadic, 21 familial) and 35 clinically unaffected but at-risk individuals. Participants' DNA was screened for genetic variation in 46 MND-associated genes using Sanger sequencing, Illumina SNP microarray, repeat-primed PCR for C9orf72, and an Invitae gene panel. Clinical phenotypes mirrored European trends: males and spinal-onset cases had earlier disease onset. Thirty-three participants (17.9%) carried known pathogenic variants: 24 had C9orf72 repeat expansions, and 9 had pathogenic SOD1 variants (p.(Ile114Thr) and p.(Glu101Gly)). All New Zealand SOD1 p.(Ile114Thr) cases (n = 4) were distantly related to each other and to over 30 Australian cases with the same variant. Variants of interest were found in 14 participants with the splicing variants DCTN1:c.279+1G>C and ATP13A2:c.2412G>A, p.(Lys804=) subject to further study. Notably, 48.4% of pathogenic variants were in pre-symptomatic, unaffected individuals with family history, highlighting the importance of offering cascade testing and symptom surveillance for families, particularly as gene-specific treatments emerge.