Prospective Psychometric Evaluation Study of a Patient-reported Outcomes (PRO) Instrument for Congenital Thrombotic Thrombocytopenic Purpura (cTTP, Upshaw-Schulman Syndrome [USS], Hereditary Thrombotic Thrombocytopenic Purpura [hTTP]

Inclusion criteria:

The participant is an adolescent aged 12 to 17 years or an adult aged ≥18 years;
The participant has been diagnosed with congenital thrombotic thrombocytopenic purpura (cTTP) and is currently receiving prophylactic or on-demand treatment with fresh frozen plasma (FFP), or solvent detergent (S/D) plasma, or Von Willebrand Factor/Factor VIII (VWF/FVIII) concentrates;
In the instance that the participant is identified and recruited remotely (Direct-to-Patient (DtP) recruitment), access to the internet and possession of an internet-connecting device is required;
The participant has provided informed consent, and in the instance that the participant is an adolescent, a legal guardian has provided informed consent and the adolescent has provided assent.

Exclusion criteria:

The participant cannot read nor write;
The participant is non-English speaking;
The participant is currently participating in a clinical trial.