Individuals with BWS may grow at an increased rate during the latter half of pregnancy and in the first few years of life. Growth parameters typically show height and weight around the 97th percentile with head size closer to the 50th percentile. Adult heights are generally in the normal range.Abnormal growth may also manifest as hemihyperplasia and/or macroglossia; the latter can lead to difficulties in feeding, speech and less frequently, sleep apnea. A recognizable facial gestalt is common and may include prominent eyes with infraorbital creases, facial nevus flammeus, midfacial hypoplasia, macroglossia, full lower face with a prominent mandible, anterior earlobe creases and posterior helical pits3. The Beckwith-Wiedemann syndrome facies often normalizes across childhood so that evaluation of adolescents or adults suspected to have BWS benefits from assessment of early childhood photographs. Development is usually normal unless there is chromosome 11p15.5 duplication or serious perinatal complications, including prematurity or uncontrolled hypoglycemia. Hypoglycemia is reported in 30-50% of babies with BWS,likely caused by islet cell hyperplasia and hyperinsulinemia.Diagnosis:Careful cytogenetic analysis of the 11p15 region and fluorescent in situ hybridization (FISH) can be used to recognize the rare translocations, inversions and trisomies.Molecular diagnosis is difficult, mostly because of the large spectrum of genetic and epigenetic abnormalities. Molecular tests must differentiate the various abnormalities in the 11p15 region: patients with 11p15 paternal UPD, patients with hypermethylation of the H19 gene, patients with demethylation of the KCNQ1OT1 gene and patients with a mutation in the CDKN1C gene. As demethylation of the KCNQ1OT1 gene is never associated with abnormal methylation of the H19 gene except in patients with 11p15 paternal UPD, analysis of the methylation status of both the KCNQ1OT1 and H19 genes leads to the diagnosis of more than 90% of 11p15 defects.Isolated demethylation of the KCNQ1OT1 gene.
- Isolated hypermethylation of the H19 gene.
- It is not yet possible to determine precisely the percentage of cases with epigenetic defects displaying a microdeletion of IC1 or IC2.
- Hypermethylation of the H19 gene associated with demethylation of the KCNQ1OT1 gene is indicative of 11p15 paternal UPD, which should be confirmed by analysis of markers of the 11p15 region and of parental DNA. 11p15 paternal UPD always occurs as mosaicism and, because tissue distribution of mosaicism is variable, tissue from a second source (such as fibroblasts) may be helpful.
- If the methylation status of the KCNQ1OT1 and H19 genes is normal, then sequencing of the CDKN1C gene is indicated, particularly in patients with exomphalos and/or a family history of BWS.
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