ALPS is like an umbrella with three handles. Each handle is a different thickness representing the three different known forms of ALPS. The thickest handle is the form that has the FAS gene mutation and accounts for 70-75% of the cases of ALPS that has been seen and studied (the mutation they just tested Phoebe for). The other two handles account for the remaining 25-30% of ALPS cases, which are the two rarer forms of this rare disease.
Phoebe's test showed no FAS mutation. They suggest further testing including genetic counseling.
This means that she has one of the rarer forms of a rare disease.