One of the biggest mystery of this medical era???
Cause of many diseases having an unknown cause. (Idiopathic etiology)
So much researches and work is done and still working on this topic to find out the cause of such diseases.
For example Cancer is the most common uncontrolled cell division and growth which eventually forms a tumor. Cancer has many forms and names according to the area and location of the tumor. Cancer can grow spread and metastasize.
Some times the cause of cancer is out of our hands and it's found in our genes. A mutated gene? There are so many diseases based on sudden gene mutations for an unknown reason.
What's that? Gene is the building block of our DNA, DNA is our genetic material that describes our genetic information and characteristics. Any change in the sequence of a gene is called gene mutation which has an unknown cause.
Do you know why this happens when a disease follows an unknown cause???
Why genes get mutated?
Why a healthy couple has a mentally or physically handicapped child?
Why a young energetic person suddenly diagnosed with a fatal disease?
Let's consider it!!!
Sit and think about this!!!
Just have a look at your source of earning!!!
If you are using the right means and earning with your best efforts nothing can affect your lifestyle or your genes except Allah's will.
But if you're not using right means for source of income, earning money through cheating, stealing, corruption, murder, interest, eating the food from the plate of an orphan, keeping the share of your siblings, or any means that involves haram for you. This kind of money can give you a luxurious life but can't gift you and your generation a healthy life.
Haram earning travel in your generations and left the effects like diseases which have an unknown cause. But this is not the only reason so many other causes can correlate but if you're having haram earning then consider your lifestyle that how much you are disturbed in spite of having a luxurious life.

"O mankind: Eat of what is lawful and good on earth" (Quran 2: 168)

“They ask you about wine and gambling. Say, "In them is a great sin and [yet, some] benefit for people. But their sin is greater than their benefit…"”
(Quran 2:219)

“They ask you about wine and gambling. Say, "In them is a great sin and [yet, some] benefit for people. But their sin is greater than their benefit…"”
(Quran 2:219)

The Prophet (peace and blessings of Allah be to him) said:

“A time will come upon the people when they will not care as to how he gets his money whether legally or illegally.”
[Bukhari]

If you are encountering a disease with an unknown cause then first of all go for self-analysis if you're earning haram, eating your children haram, and collecting haram then please stop doing this and protect your generations from the side effects of haram money and food. This causes gene mutation which travels in generations.
But if you're not earning haram then and God decided a disease for you then He might be checking your faith upon Him. Be stable in the time of hardship, remember Him in every breath and He will definitely remember you.

"Everything good that happens to you (O Man) is from God, everything bad that happens to you is from your own actions". (Quran 4:79)

"And when I am ill, it is He who cures me". (Quran 26:80)