I have an autistic sister - this is a developmental disorder that impacts her social interaction and communication.
Well is there a medical cure for autism?
No; there is therapy to help mange some of the behaviours but no cure.
So how is the therapy done? 
The therapy is used to help autistic people learn to correct their behaviours - like looking people in the eye when they speak, or teaching them epathy skills.
Empathy skills ? How is this approach applied?More so ,what's the origin of autism itself,is it hereditary or genetic?
Autism isn't hereditary, risk factors are things like drug and alcohol use in pregnancy, but there are environmental causes too. 
Yea the environmental causes,how does it translate in autistic behavioural patterns?
growth restriction, and autoimmune diseases. Controversies surround other proposed environmental causes; for example, the vaccine hypothesis, which has been disproven. Autism affects information processing in the brain by altering connections and organization of nerve cells and their synapses. How this occurs is not well understood. In the DSM-5, autism and less severe forms of the condition, including Asperger syndrome and pervasive developmental disorder not otherwise specified (PDD-NOS), have been combined into the diagnosis of autism spectrum disorder (ASD).
Early behavioral interventions
or speech therapy can help children with autism gain self-care, social, and communication skills. Although there is no known cure, there have been cases of children who recovered. Not many children with autism live independently after reaching adulthood, though some are successful. An autistic culture has developed, with some individuals seeking a cure and others believing autism should be accepted as a difference and not treated as a disorder.
Globally, autism is estimated to affect 24.8 million people . In the 2000s, the number of people