For many years, the high prevalence of the fragile X syndrome was thought to be caused by a high mutation frequency. The recent isolation of the FMR1 gene and identification of the most prevalent mutation enable a more precise study of the fragile X mutation. As the vast majority of fragile X patients show amplification of an unstable trinucleotide repeat, DNA studies can now trace back the origin of the fragile X mutation. To date, de novo mutations leading to amplification of the CGG repeat have not yet been detected. Recently, linkage disequilibrium was found in the Australian and US populations between the fragile X mutation and adjacent polymorphic markers, suggesting a founder effect of the fragile X mutation. We present here a molecular study of Belgian and Dutch fragile X families. No de novo mutations could be found in 54 of these families. Moreover, we found significant (P < 0.0001) linkage disequilibrium in 68 unrelated fragile X patients between the fragile X mutation and an adjacent polymorphic microsatellite at DXS548. This suggests that a founder effect of the fragile X mutation also exists in the Belgian and Dutch populations. Both the absence of new mutations and the presence of linkage disequilibrium suggest that a few ancestral mutations are responsible for most of the patients with fragile X syndrome.

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Addressing a significant gap in the literature, this study commences with a dual focus: assessing sustainability evaluations, both within the airport sector and across a broader range of industries. Through a comprehensive review of 33 academic articles specific to airport sustainability, we delve into a detailed analysis of 16 papers that implement specific methodologies for assessing airport sustainability performance. These methodologies are compartmentalized into three primary categories: Data Envelopment Analysis (DEA) and its extensions, Hybrid Multiple-Criteria Decision Making (MCDM), and composite index-based assessments. A meta-review extending beyond the airport sector uncovers common issues across industries, including the absence of universally adaptable sustainability frameworks and an overemphasis on assessment, overshadowing the essential role of sustainability accounting. Our findings underscore the need for a paradigm shift from pure evaluation towards a holistic approach to sustainability modeling. With systems thinking at its core, this approach allows a better grasp of the complex interactions and feedback loops within sustainability systems and provides a strategy to tackle inherent trade-offs and compensatory effects. By exposing gaps in current practices, this study paves the way for future research, particularly the integration of systems thinking with MCDM, promising to enrich sustainability evaluation and management methodologies, ultimately facilitating more sustainable airport operations.

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