Page 213 - Characterization of genetic neurodevelopmental disorders at adult age, with a focus on 22q11.2 deletion syndrome - Emma Boersma

General discussion and future perspectives
and otolaryngologic examinations are part of standard routine care at the
22q11.2 expert clinic at Maastricht University Medical Center. Only a minority
of adults were examined upon indication for (suspicion of) ophthalmic,
otolaryngologic or movement disorders. Limitations mainly related to the
retrospective or cross-sectional design of most studies. Data concerning
the medical history may not be complete resulting in an underestimation of
the studied conditions. In some cases, patients that were examined were
noncooperative or had difficulties with performing tasks, which most likely
concerned individuals with a more severe phenotype, that may have resulted
in a slight underestimation of the prevalence rates of studied conditions.
However, referral bias may have resulted in higher prevalence rates because
individuals with 22q11.2DS with a more severe phenotype may have higher
probabilities of being referred to a 22q11 specialty clinic. Age of onset
of conditions such as hearing loss, refractive errors or sleep apnea was
often not reported in the medical files, and was therefore not subject of
study. This hampers the ability to differentiate between manifestations with
early- or adult-onset, which is important information for the improvement
of screening recommendations. In addition, the average age of the study
participants in most studies was still quite young. Because most conditions
may increase with age, this will have resulted in an underestimation of
prevalence rates of late-onset conditions.
Comparisons of studied conditions with previous studies was often com-
plicated due to the use of different definitions, cut-off values and measure-
ment techniques or because other studies did not distinguish findings in
children from findings in adults.63-65
The systematic literature review, described in chapter 2, had some specific
limitations of which the most important one relates to the definition
that was used for a GND. Inclusion of all conditions listed in HPO as
“neurodevelopmental abnormality”, in addition to the large number and
wide spectrum of genetically and clinically heterogeneous disorders
and the absence of a perfect classification system, may have resulted in
the inclusion of conditions that should not be considered to affect brain
development.
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