Syndrome
Disease
suffix, な adjective
Multiple symptoms combine to make a syndrome. If you see this at the end of a word, you know it means "______ syndrome," or else indicates some kind of health condition.
〜症 is used in medical terms for certain health conditions, symptoms, or syndromes, like 熱中症 (heatstroke) or 認知症 (dementia).
Since this is attached to things, it's treated like a jukugo word, so the on'yomi reading is used here.
岸田さんのエッセーには、車いすのお母さんとダウン症の弟さんとの日々がつづられています。
In Ms. Kishida's essay, she writes about her daily life with her mother in a wheelchair and her brother with Down syndrome.
熱中症になるといけないので、こまめに水分をとってくださいね！
You must not get heatstroke, so please make sure to frequently stay hydrated!
それって、認知症の初期症状じゃないですか？
Aren’t those early symptoms of dementia?
妻の神経性ヒステリー症について、医者に相談しなくてはいけません。
I should consult a doctor about my wife’s neurotic hysteria.