Is there a mild form of achondroplasia? A semi-dwarf?

Several short types. The commonly seen form of achondroplasia is an autosomal dominant form of short limb dwarfism. 80% are new mutations but it can be passed parent to child at a 50%/pregnancy rate. A fetus with a pair of achondroplasia genes has a severe condition & is unlikely to survive infancy. Their are a number of conditions that produce "little people" & you may be thinking of another condition.