Autism

Autism is a developmental disorder characterised by disturbance in language,
perception and socialisation. There is a failure to relate to people and
situations and the person appears to have difficulty making sense of incoming
information. There may be a tendency to repetitious movement (rocking or
clapping for example) or an inappropriate focus on detail. There can be
withdrawal from a world that appears frightening or unreasonable tantrums.

Although autism appears to have some genetic links there is recent evidence
to suggest that this may be triggered by some type of environmental influence,
which could possibly be either a cerebral allergic reaction or a chemical sensitivity that impairs brain metabolism.

It has also been hypothesised that incomplete digestion of casein in milk
products and gluten in wheat products may result in the formation of proteins
fragments (ezophins) that may mimic opiate (like hormones and neurotransmitters
used by the brain) resulting in a scrambling of sensory input and processing.

Secretin is hormone produced by the duodenum and jejunum portions of the
intestine when acidic chyme (partially digested food) enters the intestine. It
stimulates the secretion of pancreatic juices. If the stomach is not able to
acidify food sufficiently to stimulate the production of secretin then the maldigestion of proteins can occur.

I presume this is where the connection between autism and the hormone secretin occurs.  In answer to your question (as to whether supplementation with secretin would help someone with Autism), I know of no natural product in which secretin is specifically found, my suggestion would be to use a food enzyme product that contains pancreatic enzymes (protease, amylae, lipase).
I usually recommend a product which is entirely plant derived, contains an effective amount of digestive enzymes and are extremely well tolerated.
Go to On-line shop for enzymes products.

It would also be appropriate to check for food intolerances, both dairy and
gluten, improve liver detoxification, increase anti-oxidant intake and try
supplements that increase brain energy. These would include products such as
Co enzyme Q10, and NADH (Nicotinamide Adenine Dinuclotide).