Abnormal immune system in Down syndrome: allergic sensitization and hepatitis B vaccination status 2 - blood sample

Several studies have shown that Down syndrome (DS) is associated with an
aberrant immune system. On the one hand there are data showing that children
with DS have fewer allergies, on the other hand DS frequently leads to
recurrent wheezing and airway infections resulting in tests and treatment for
allergy, especially at a young age. There are no large studies showing the
prevalence of allergic sensitization in people with DS. This study aims to fill
this knowledge gap. Besides, some studies describe a decreased response to
vaccinations, among others to hepatitis B (HBV) vaccination. It is important to
have data to decide whether it is clinically relevant to routinely determine
the titer after HBV vaccination in DS and to offer booster vaccinations . The
long term course of the anti-HBs-titer is not yet sufficiently clarified.

Determine whether the prevalence of allergic sensitilization, defined as at
least one allergen specific IgE with a concentration of >= 0,35 kU/l, is lower
in people with than without DS. Analyse whether this prevalene is depending on
age, how many patients with DS and allergic sensitization have symptoms and how
often diagnostics and/or treatment for asthma and/or other allergies is
performed in DS. Also, the concentration of total IgE is determined. Besides,
it is determined whether a protective titer against HBV, defined as an
anti-HBs-titer >=10 IE/l, is less often found in persons with than without DS,
and what is the titer of anti-HBs in the long term.

Multicenter, cross-sectioneel study. The will be compared with people without
DS from the literature.
An extra 4 ml (2-16 years) or 7 ml (>=16 years) of blood will be sampled for
study purposes, but only during an already planned venepuncture. The presence
of sensitization will be determined using total IgE, inhalation antigen mix and
food antigen mix, with determination of specific IgE*s in case of a positive
mix test result. Besides, the titer of anti-HBs will be determined. Informed
consent will be asked from the parents and - if possible - the patient >=12
years. With retrospective chart review and a short questionnaire for the
parents at inclusion, the presence of allergy related symptoms, the use of
diagnostics and/or treatment, as well as the HBV vaccination status will be
analyzed.

Participation in the All-HBV-DS2 - blood sample study does not offer the
patient direct benefit, but there are no real risks either. The only extra
effort that is asked of parents and patient, is the completion of a short
questionnaire. The risk of taking an extra 4 ml (<16 years) or 7 ml (>=16 years)
of blood during an already planned venepuncture is negligible. More data on the
prevalence of allergic sensitization and the response to HBV vaccination is
useful for clinical decision making. Especially at a young age, other problems
can cause symptoms like wheezing, for instance anatomical abnormalities.
Besides, this study can produce more data to decide whether it is clinically
relevant to routinely measure the titer after HBV vaccination in DS. This study
could lead to new insights regarding the national vaccination program
specifically for DS.