Yup i had the same thing happen to me.
My rat had a litter of 6 but unfortunatly passed away a few day later from what to this day i still iam not sure of .....
Now back to the topic, I had raised the pups up myself with a great mash that i have used before and had produced some nice fat rats with. But these little white guys never grew bigger than a small adult mouse!
It was quite odd.... a friend took them from me to sell as "Dwarf Rats" lol.......and they sell well i should say... lol
One thing i do know is to get a "dwarf" anything... your supose to breed the runts. As far as i have heard that is how they get Tea cup bunnies... But i could be wrong..lol I only worked with small animals for a short time.
Maybe your rats just have a "runt" Gene showing up?
~*Ciddian*~
BigAl'sOnline
BigAlsOnline