you can get custody of child if you are able  to prove wife is not mentally fit 

you should rely upon testimony of doctors to prove mother is mentally un fit suffering from bipolar disorder 

Testimony of expert witnesses would be subject to cross examination 

Testimony of doctors wound help you in obtain child custody of your minor child 

A father  is entitled to full custody of child after he/she crosses five years. The child is four years old and it just matter of one year, in such Court will be reluctant of take the child out of custody of mother. All the mental disorders are not likely to interfere in motherly conduct by her. Further, if there are other members of family who can take care of child, that will additional factor against you.

- Under Hindu law, A mother usually gets custody of the minor child, under the age of five and fathers get custody of older boys, but it is not a strict rule and is primarily decided based on the child’s interests.

- The choice of a child above the age of nine is considered, and further a mother who is proven to neglect or ill-treat the child is not given custody.
- Since, She is suffering from the said diseases and the doctors have already confirmed for the same , then you are legally entitled to get the custody of minor child.

- You can file a petition before the court for getting custody of the child. 

The child's interest is paramount while deciding about the custody of the minor child by the court.

In your case the circumstances are favoring you especially since you have supporting documents to prove that your wife is mentally unfit and the said disease she is affected may cause harm to the minor child, hence the child's interests, welfare and risk of life is at jeopardy 

The testimonies given by the medical examiners in the previous case may come to your support to grant the child custody, hence you may file the child custody case immediately without any delay. 

The medical certificates as well as the doctors' testimonies given before another court can be produced as documentary evidences on your side to enable the court to pass an order in your favor. 

Yes if you prove the same you can get it for child welfare 

Hello,

1. You as father, a natural guardian can get the custody of the 4 year old son considering the welfare and safety of the child.
2. The testimonies of the doctors can come to your aid in getting a favourable verdict. 
3. However, factors like her being in a responsible employment and her own testimonies that the child needs to be in her custody and taking away the child can impacther mental health arrangements that can be in her favour.

Dear client I am sorry to hear that but in the case you may approach the court for the custody of child on the basis of his or her safety and best interest.

In child custody cases the welfare of the child is of paramount importance, so if the mother is unfit to take care of the child owing to her medical condition, then you can get custody of the child.

The expert opinion rendered by the doctors as well as her medical records would help you a lot in getting the custody of the child. 

If the state of your wife's mental health is proved by medical evidence to the satisfaction of the court, your plea for child custody will stand on a firm ground.

1. Yes you can get child's custody on the grounds you have stated. 
2. Regarding preecedents (case laws) are you appearing in court proceedings as party in person? (ie without appointing any lawyer?) If you aren't, then your counsel (advocate)  should handle that. If you are, no counsel will supply you case laws in this manner. You have to appoint him/ her as your counsel.

Yes, you can get custody of your son under guardian act section 14. And yes citation are available.