Hi, I know this can be so difficult, for the family and for your brother. Does he believe there is a God? [1 corinthians 1:27-29] was spoken just for people like him. God makes no mistakes and there is a very special reason for your brothers situation.
Father, God, I come to you this morning to lift up this family to your loving care. Lord, there are many hurts, disillusions,and pain here. Lord,God I ask that first you would heal the spirit of this young man, let him see Lord, how special he is to you and how much you love him. Father, your word says that you use the weak,and lowly to shame the strong and mighty. Lord, what a blessing to be used of you no matter our circumstance, because you are able. Lord, I ask that you will show the Doctors what the problem is and that they will be able to help with this condition. Lord, God, I just lift up this family,and lay their burdens at your feet, at the foot of the cross, and pray that you would heal the hurts, mend the damaged emotions,and bring this family back together in your love. This is the time father when family needs to be together, support each other, and love each other. Lord, As this family comes together,I ask that you would strengthen them and bring Joy back into their lives and praise you Father, for the healing and the peace that comes with a right relationship with you. Bless them this day and in the days to come, let their cup overflow with blessings, and peace. Lord I thank you for the answer to this and all the prayers going up for this family, and praise you Father for the healing you are going to bring to this family. Thank you Father, for providing the way to come to you, especially in circumstance such as this.
Lord, I ask that you would comfort them in these times of trouble, and take them to the light. Lord, I thank and praise you now and forever. In the name of Jesus I pray
Amen 

Dear ylceleb
Your brother is in my prayers. God will hold him safe. He is loved and treasured and God will draw him to Himself, even if it takes time.
Your simple presence in your brother's life and your love for him, is a way that God is touching him already.
I will pray for his health - that the doctors will find the right treatment for him and that he will be more at peace with life.
God bless you.