Epidemiology of spinal muscular atrophy in Aotearoa-New Zealand

The advent of three effective disease modifying therapies for SMA has highlighted the need to understand the epidemiology of spinal muscular atrophy (SMA) and its disability impact.

We aimed to establish the nationwide incidence and prevalence of SMA in Aotearoa-New Zealand, and to estimate the patients' disability and the impact of this on health resource utilisation.

We used multiple sources to identify patients with SMA and verified the diagnosis, disabilities and resources utilisation by review of the individual patient notes and genetic results. The four year incidence period was from 1st July 2015 to 30th June 2019. Prevalence date was 1st March 2019. Of note, this time period pre-dated access to disease modifying therapy in New Zealand. Census data for 2018 was used for denominators. Descriptive statistics and capture-recapture were used to analyse the data. For context, we reviewed international SMA epidemiology.

The incidence per 100,000 live births was 8.0 (95% confidence interval (CI): 4.8-12.5). The standardised prevalence rate of SMA on 1st March 2019 was 1.78 per 100,000 (95% CI: 1.24, 2.33). Prevalence was significantly lower amongst Māori at 0.34 (95% CI: 0.08, 1.13; p = 0.006). Substantial decline from best motor milestone performance was seen; seven patients with SMA1 died without access to disease modifying therapy. 74% of the total cohort used wheelchairs. 23% required respiratory support. 62% had scoliosis, of whom 61% had had surgery. Surviving SMA1 patients had very high health service utilisation.

Incidence and prevalence figures match closely with international studies. This is the first record of low SMA rates in Māori. While the largest burden of disease falls on patients with SMA1 and 2 there is still substantial use of health resources among SMA3 and SMA4 patients.