Complete English summary here. (And, you probably want to check this post ^^)
NOTE: this is NOT an FMA prototype story Arakawa-sensei wrote about 10 years ago.
QUOTE ("Anime News Network")
The May issue of Square Enix's Monthly Shonen Gangan magazine is announcing on Tuesday that the July issue will publish Hiromu Arakawa's Fullmetal Alchemist "Prototype" manga as a one-shot in June.
Source - Anime News Network
I remember I've read something about that "prototype manga". It has flying squirrels in it o.O
Arakawa seems to not let FMA go, does she. Well, I'm glad, because I will get something similliar to that old, good, monthly waiting for new chapter.