Prader-Willi syndrome: A primer for clinicians

This manuscript was prepared as a primer for clinicians-to serve as a resource for those of you who care for children and adults with Prader-Willi syndrome on a daily basis in your practices. Appropriate and anticipatory interventions can make a difference.First described by Prader, Labhart and Willi in 1956 [1], this syndrome represents the most common genetic cause of obesity with an estimated incidence of 1:15,000 to 1:25,000 live births [2,3]. Reported prevalence rates vary among countries but both sexes appear to be equally affected. Prader-Willi syndrome (PWS) is the first human syndrome identified with genomic imprinting [4]. The original descriptions of this syndrome included short stature, hypotonia, hypogonadism and mental retardation [1]. As infants grow to age 2-4 years, failure to thrive related, at least in part, to poor muscle tone and poor suck are replaced by increased appetite and food intake resulting in obesity and its comorbidities. Early diagnosis and intervention to prevent obesity and the associated complications are critical.Candidate genes for Prader-Willi syndrome have been located on the long arm of chromosome 15q11-q13. These genes are physiologically imprinted and silenced on the maternally inherited chromosome. PWS arises when the paternally derived genes are missing, defective or silenced. The frequencies of each are shown in Table 1.High resolution chromosomal analysis (HRCA) is done along with the fluorescence in situ hybridization (FISH) to detect deletions and translocation of chromosome 15 [5]. Deletion has been divided in type I (TI) and II (TII) according to the size. Studies indicate that individuals with the TI (~500 kb larger than TII) generally have more behavioral and psychological problems than individuals with the TII and UPD [6]. Negative FISH or karyotype analysis does not exclude the diagnosis and thus if done first should be followed by DNA methylation analysis. DNA methylation analysis is the only technique which ca