Repeat contractions and expansions are the reason why SCA27B can appear to "skip" generations in a family. If we were to look at a family with SCA27B, you might see something like the following where the condition has "skipped" from a grandfather to his grandson: 

• A male has SCA27B with 330 repeats in one copy of FGF14 and 60 repeats in the other. 

• He has a daughter. The FGF14 copy with more repeats is inherited by the daughter from her father, but the number of repeats contracts to 200. She will not develop SCA27B. 

• This female has a son. She passes on her FGF14 copy with 200 repeats, which expands to 315 repeats when it is inherited by her son. He will eventually develop SCA27B.