Hong Shao1, Va Lip, Bai-lin Wu. 1. Department of Laboratory Medicine, Children's Hospital and Harvard Medical School, Boston, MA 02115, USA.
Abstract
OBJECTIVE: Prader-Willi syndrome (PWS) is characterized by severe hypotonia and feeding difficulties in early infancy, followed by excessive eating and gradual development of morbid obesity in later infancy or early childhood. Patients with PWS are often too young to manifest sufficient features or have atypical findings, making genetic testing important to confirm the diagnosis of PWS. Approximately 99% of patients with PWS have a diagnostic abnormality in the parent-specific methylation imprint within the Prader-Willi critical region (PWCR) at chromosome 15q11.2-q12. Of them, 70% have a paternal deletion; 25% have a maternal uniparental disomy (UPD); and <5% have a mutation in the imprinting center. METHODS: Current techniques can identify a diagnostic abnormality, such as paternal deletion or maternal UPD for most of patients with PWS, but they are labor-intensive and cost-expensive. Multiplex ligation-dependent probe amplification (MLPA) is a novel, simple, and cost-effective technique for analysis of relative quantification in a single assay, which has recently been applied for the detection of genomic deletions, duplications, and amplifications in a variety of genes. RESULTS: Six out of 20 patients referred for genetic diagnosis of PWS were found to have a deletion by MLPA, confirmed by FISH and DNA methylation analysis with 100% concordance. CONCLUSION: MLPA's high sensitivity and specificity for deletion detection is the same as FISH or Southern blot based analysis. Additional collaborative effort for developing and validating the complete MLPA-PWS assay, for not only detecting deletion but also identifying methylation abnormality, is on going.
OBJECTIVE:Prader-Willi syndrome (PWS) is characterized by severe hypotonia and feeding difficulties in early infancy, followed by excessive eating and gradual development of morbid obesity in later infancy or early childhood. Patients with PWS are often too young to manifest sufficient features or have atypical findings, making genetic testing important to confirm the diagnosis of PWS. Approximately 99% of patients with PWS have a diagnostic abnormality in the parent-specific methylation imprint within the Prader-Willi critical region (PWCR) at chromosome 15q11.2-q12. Of them, 70% have a paternal deletion; 25% have a maternal uniparental disomy (UPD); and <5% have a mutation in the imprinting center. METHODS: Current techniques can identify a diagnostic abnormality, such as paternal deletion or maternal UPD for most of patients with PWS, but they are labor-intensive and cost-expensive. Multiplex ligation-dependent probe amplification (MLPA) is a novel, simple, and cost-effective technique for analysis of relative quantification in a single assay, which has recently been applied for the detection of genomic deletions, duplications, and amplifications in a variety of genes. RESULTS: Six out of 20 patients referred for genetic diagnosis of PWS were found to have a deletion by MLPA, confirmed by FISH and DNA methylation analysis with 100% concordance. CONCLUSION: MLPA's high sensitivity and specificity for deletion detection is the same as FISH or Southern blot based analysis. Additional collaborative effort for developing and validating the complete MLPA-PWS assay, for not only detecting deletion but also identifying methylation abnormality, is on going.