When you ask a question and only get one reply

Depends on what the question was.

What was the question?

It was about atypical autism vs pdd nos . 

I've seen this one, but it's a difficult question, as you might need someone who is an expert in the diagnostic manual and ASD to answer this. I didn't feel confident to give you an answer without lots of research. I know that PDD-NOS is in DSM-4 but became part of ASD in DSM-5. But I am not familiar with the definiation of atypical autism at all. The lack of reply was mainly my insufficiency of knowledge on this topic, and I would need to do more research to give an answer.

Have you tried searching wikipedia? 
https://en.wikipedia.org/wiki/Pervasive_developmental_disorder_not_otherwise_specified 

"A pervasive developmental disorder not otherwise specified (PDD-NOS) is one of the four autism spectrum disorders (ASD)^[1] and also one of the five disorders classified as a pervasive developmental disorder (PDD).^[2] According to the DSM-IV, PDD-NOS is a diagnosis that is used for "severe and pervasive impairment in the development of reciprocal social interaction or verbal and nonverbal communication skills, or when stereotyped behavior, interests, and activities are present, but the criteria are not met for a specific PDD" or for several other disorders.^[3] PDD-NOS is often called atypical autism,^[4] because the criteria for autistic disorder are not met, for instance because of late age of onset, atypical symptomatology, or subthreshold symptomatology, or all of these.^[3] Even though PDD-NOS is considered milder than typical autism, this is not always true. While some characteristics may be milder, others may be more severe.^[5]"

According to this paragraph, they say "PDD-NOS is often called atypical autism"

I've seen this one, but it's a difficult question, as you might need someone who is an expert in the diagnostic manual and ASD to answer this. I didn't feel confident to give you an answer without lots of research. I know that PDD-NOS is in DSM-4 but became part of ASD in DSM-5. But I am not familiar with the definiation of atypical autism at all. The lack of reply was mainly my insufficiency of knowledge on this topic, and I would need to do more research to give an answer.

Have you tried searching wikipedia? 
https://en.wikipedia.org/wiki/Pervasive_developmental_disorder_not_otherwise_specified 

"A pervasive developmental disorder not otherwise specified (PDD-NOS) is one of the four autism spectrum disorders (ASD)^[1] and also one of the five disorders classified as a pervasive developmental disorder (PDD).^[2] According to the DSM-IV, PDD-NOS is a diagnosis that is used for "severe and pervasive impairment in the development of reciprocal social interaction or verbal and nonverbal communication skills, or when stereotyped behavior, interests, and activities are present, but the criteria are not met for a specific PDD" or for several other disorders.^[3] PDD-NOS is often called atypical autism,^[4] because the criteria for autistic disorder are not met, for instance because of late age of onset, atypical symptomatology, or subthreshold symptomatology, or all of these.^[3] Even though PDD-NOS is considered milder than typical autism, this is not always true. While some characteristics may be milder, others may be more severe.^[5]"

According to this paragraph, they say "PDD-NOS is often called atypical autism"