Methylation analysis and diagnostics of Beckwith-Wiedemann syndrome in 1,000 subjects

Abstract

Background: Beckwith-Wiedemann syndrome (BWS), a congenital overgrowth disorder with variable expressivity and a predisposition to tumorigenesis, results from disordered expression and/or function of imprinted genes at chromosome 11p15.5. There are no generally agreed clinical diagnostic criteria, with molecular studies commonly performed to confirm diagnosis. In particular, methylation status analysis at two 11p15.5 imprinting control centres (IC1 and IC2) detects up to 80% of BWS cases (though low-level mosaicism may not be detected). In order to evaluate the relationship between the clinical presentation of suspected BWS and IC1/2 methylation abnormalities we reviewed the results of >1,000 referrals for molecular diagnostic testing.

Results: Out of 1,091 referrals, 507 (46.5%) had a positive diagnostic test for BWS. The frequency of tumours was 3.4% in those with a molecular diagnosis of BWS. Previously reported genotype-phenotype associations with paternal uniparental disomy, IC1, and IC2 epimutation groups were confirmed and potential novel associations detected. Predictive values of previously described clinical diagnostic criteria were compared and, although there were differences in their sensitivity and specificity, receiver operating characteristic (ROC) analysis demonstrated that these were not optimal in predicting 11p15.5 methylation abnormalities. Using logistic regression, we identified clinical features with the best predictive value for a positive methylation abnormality. Furthermore, we developed a weighted scoring system (sensitivity 75.9%, and specificity 81.8%) to prioritise patients presenting with the most common features of BWS, and ROC analysis demonstrated superior performance (area under the curve 0.85, 95% CI 0.83 to 0.87) compared to previous criteria.

Conclusions: We suggest that this novel tool will facilitate selection of patients with suspected BWS for routine diagnostic testing and so improve the diagnosis of the disorder.

Keywords: 11p15; Beckwith-Wiedemann syndrome; Diagnostic criteria; Imprinting; Scoring system.

Figure 1

Frequencies of Beckwith-Wiedemann syndrome clinical features according to molecular subtype. (a) Hemihypertrophy, (b) macroglossia, (c) facial naevus flammeus, (d) ear creases/pits, (e) exomphalos, (f) organomegaly, and (g) embryonal tumours. ALL-MUT, all mutations; IC1, imprinting centre 1; IC2, imprinting centre 2; NIL, no mutations; pUPD, paternal uniparental disomy.

Figure 2

Predicted and observed probabilities for a Beckwith-Wiedemann syndrome methylation abnormality based on the new scoring system.$\left(\mathit{\text{methylation}}\mathit{\text{abnormality}}\right)=\frac{{\mathit{e}}^{‒2.47\mathit{+}0.808\left(\sum \mathit{\text{scores}}\right)}}{1+{\mathit{e}}^{‒2.47\mathit{+}0.808\left(\sum \mathit{\text{scores}}\right)}}$.

Figure 3

Receiver operating characteristic curves comparing the proposed new scoring system against existing clinical diagnostic criteria for a positive Beckwith-Wiedemann syndrome methylation abnormality. ^†Complete classification of Beckwith-Wiedemann syndrome was used (see Table 5).