People with Down syndrome are much more likely to die from untreated and unmonitored infections than other people.
Children with Down syndrome are much more likely than other children to develop leukemia
Children with Down syndrome are more likely to have epilepsy [...] Almost half of people with Down syndrome who are older than age 50 have epilepsy.
And from this paper[2]:
Clinical research and longitudinal studies consistently estimate the lifetime risk of dementia in people with Down syndrome to be over 90%. Dementia is rare before the age of 40 years, but its incidence and prevalence exponentially increase thereafter, reaching 88–100% in persons with Down syndrome older than 65 years. [...] In a longitudinal study of adults with Down syndrome, dementia was the proximate cause of death in 70% of cases.
Saying they can have extreme health issues does not seem excessive given the above IMHO.
[1]: https://www.nichd.nih.gov/health/topics/down/conditioninfo/a...