Clinical and laboratory diagnosis of Prader-Willi syndrome

Prader-Willi syndrome is a disorder of structural and functional alteration s including developmental, behavioral, neurologic, endocrine, and structura l abnormalities, that is due to dosage imbalance of the genes on 15q11-q13 relating to genetic imprinting in that region. Most of features of Prader-W illi syndrome are nonspecific and vary with age, genetic basis, race, and o ther unknown factors. A number of other disorders can have similar features , depending on the age of the patient. Clinical diagnostic criteria were de veloped in 1993 that can aid the clinician and researcher in determining wh ether definitive diagnostic testing is indicated. Methylation analysis, whi ch determines whether or not relevant genes in 15q11-q13 are active, can be used to confirm or exclude the diagnosis in an affected patient. When thes e genes are inactive, which usually occurs when only maternally inherited g enes are present, Prader-Willi syndrome results. For genetic counseling pur poses, it also is possible to determine whether the disorder is due to a de letion in the paternally inherited 15q, maternal uniparental disomy 15, or a defect in the imprinting process. High-resolution chromosome analysis is useful to determine whether there is a translocation or other chromosome ab normality that caused the altered gene dosage.