"Is it true that the cause of this illness hasn't been discovered by current medical science?"
"Is it true that the cause of this illness hasn't been discovered by current medical science?"
"is it true that ~" 「〜のは本当ですか？」
"the cause of this illness" 「この病気の原因」"illness" の代わりに "disease" や "sickness" も言えます。
"hasn't been discovered" 「究明できていない」"discovered" の代わりに "determined" も使えます。
"by current medical science" 「現在の医学では」
Is it really the case that the cause of this sickness has not been identified in the field of modern medicine?
この場合、次のような言い方ができると思います。
ーIs it really the case that the cause of this sickness has not been identified in the field of modern medicine?
「現代の医学で、この病気の原因が究明されていないというのは本当ですか？」
Is it really the case that ... ? で「…というのは本当ですか？」
the cause of this sickness has not been identified 「この病気の原因が究明されていない」
modern medicine で「現代の医学」
ご参考まで！
オーストラリア 
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