Summary of the unPAD study

SUMMARY

Rationale: Primary immune deficiencies (PIDs) are rare; therefore, the European Society for Immunodeficiencies (ESID) has been running the ESID online Registry, to study these diseases. For all patients, basic characteristics are being registered at first registration and yearly thereafter in the so-called level 1 forms. Detailed characteristics of the patients can be registered in level 2 forms. Preformulated research questions underlie the questions in the forms. For specific studies, temporary level 3 forms can be added to specific disease categories. Milder forms of PID are generally not immediately life threatening, but lead to important morbidity, irreversible organ damage and ultimately loss of lifespan when they are not recognized and properly treated. These milder forms mainly comprise diseases with predominantly antibody deficiency. The criteria for clinical working definitions in the Registry are very strict. All ‘predominantly antibody deficiencies’ that do not completely fulfil all criteria should be registered under ‘unclassified antibody deficiency’. This is by far the largest group. However, it is not very well known whether and if so how they should be treated, whether treatment(s) are useful for some but not all subgroups, nor whether ‘deficiency of specific IgG (specific antibody deficiency - SPAD)’, ‘IgA with IgG subclass deficiency’, ‘isolated IgG subclass deficiency’, ‘selective IgM deficiency’ and/or ‘selective IgA deficiency’ should be considered as separate, clearly defined groups.

Objective: The primary objective of the unPAD study is to characterise ‘unclassified antibody deficiency’, for this project including ‘deficiency of specific IgG (specific antibody deficiency - SPAD)’, ‘IgA with IgG subclass deficiency’, ‘isolated IgG subclass deficiency’, ‘selective IgM deficiency’ and ‘selective IgA deficiency’ [the combined group is hereafter referred to as ‘unPAD patients’]. To this end, a set of research questions for the level 2/3 form were formulated by the antibody deficiency expert panel of the ESID Registry Working Party.

Study design: Observational cohort study using the ESID online Registry.

Study population: Patients of all ages who have given informed consent for participation in the ESID Registry, and who fulfil the ESID Registry Clinical Criteria for ‘unclassified antibody deficiency’, ‘deficiency of specific IgG (specific antibody deficiency - SPAD)’, ‘IgA with IgG subclass deficiency’, ‘isolated IgG subclass deficiency’, ‘selective IgM deficiency’ and/or ‘selective IgA deficiency’ [‘unPAD patients’] (http://esid.org/Working-Parties/Registry/Diagnosis-criteria) or CVID (control group).

Intervention (if applicable): not applicable.

Main study parameters/endpoints: The main study endpoint is the detailed description of the PID category ‘unclassified antibody deficiency’, for this project including ‘deficiency of specific IgG (specific antibody deficiency - SPAD)’, ‘IgA with IgG subclass deficiency’, ‘isolated IgG subclass deficiency’, ‘selective IgM deficiency’ and ‘selective IgA deficiency’ [‘unPAD patients’] by answering the research questions formulated by the antibody deficiency expert panel of the ESID Registry Working Party.

Nature and extent of the burden and risks associated with participation, benefit and group relatedness: not applicable. The unPAD study is an observational cohort study using data concerning patients who have already given their informed consent for registration in the ESID online Registry.

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