What are PIDs?

Prof. Helen Chapel, immunologist, answers crucial questions about primary immunodeficiencies.

Published 4 February, 2016

Primary immunodeficiencies (PIDs) are a large and growing group of over 300 different disorders caused when some components of the immune system (mainly cells and proteins) do not work properly.

Whilst PIDs are generally recognised as rare disorders, some are more common than others and taken as a whole they represent an important group of people whose lives are profoundly impacted by their condition.

PIDs are caused by genetic defects of the immune system which are hereditary. The immune system normally helps the body fight off infections by germs (or ‘micro-organisms’) such as bacteria, viruses, fungi and protozoa. Because their immune systems do not work properly, people with PIDs are more prone than other people to infections. When PIDs are left underdiagnosed or are misdiagnosed, the immune system remains defective, often leading to illness, disability, permanent organ damage or even death.

Diagnosis
Whilst it is estimated that around 60% of PIDs can be easily diagnosed with a simple and inexpensive blood tests, many PIDs remain underdiagnosed on a global scale. Hopefully, as the technical ability to identify gene defects improves, more and more genetic causes of PID will be identified.

Medicine is advancing very rapidly and novel therapies that target the specific cause of the disease are becoming available. These may have significant advantages for PID patients and it is important that patients throughout the world have access to these treatment possibilities.
Screening for some of the most severe forms of immunodeficiency, such as Severe Combined Immunedeficiencies (SCID) , will also diagnose more individuals and improve treatment outcomes.

Treatment
With appropriate access to the different and very effective therapies which can only happen if early and correct diagnosis is made, many sequelae will be avoided and lives of patients will be saved.

People with PIDs are normally treated by doctors who specialise in diseases of the immune system. How a patient is treated depends on which PID they have, and on many other factors. Treatments for PIDs include: immunuglobulin (IG) therapies, Hematopoietic Stem Cell Transplantation (BMT), gene therapy, Grantulocyte-colony stimulating factor (G-CSF), Gamma interferon, PEG adenosine deaminase, prophylactic anti-biotics, among others.

In the case of IG therapies it is important to know that different IG products are not interchangeable or mixable. IG can be administered intravenously or subcutaneously. They are considered as essential medicines for PIDs by the World Health Organisation. Intravenous immunoglobulin (IVIG) infusion usually takes 2-4 hours allowing high doses to be given and only needs to be given every 3-4 weeks which may suit some patients better. Subcutaneous immunoglobulin (SCIG) only takes 1-2 hours and can often be given at home by patients themselves, parents or carers. It may therefore be more convenient for some patients. However only small doses can be given by SC infusion, meaning they are given more frequently than IV infusions, usually once a week. A new type of SC infusion containing recombinant human hyaluronidase, known as facilitated subcutaneous immunoglobulin (FSCIG) allows patients to have SC infusions every 3-4 weeks. IG therapy should be chosen on an individualised basis, according to patient needs and preferences.

Classification
PIDs are currently classified into nine groups: predominantly antibody deficiencies; combined immunodeficiencies; combined immunodeficiencies with associated or syndromic features; diseases of immune regulation; congenital defects of phagocyte number or function, or both; defects of innate immunity; auto-inflammatory disorders; complement deficiencies, based on the main immunological defects; and phenocopies of Primary Immunodeficiencies.

For more details on the classification of PID read the IPOPI leaflet ‘How are primary immunodeficiencies classified?’

IPOPI is committed to continue to disseminate information to patients, their relatives and doctors and work towards better access to early diagnosis and treatment for all patients living with a PID.

For more information about PIDs and how they are treated, diagnosed and advice on how to stay healthy please refer to the IPOPI leaflets.