Stages of PWS

In the past, PWS was described as a 2 stage syndrome – failure to thrive (poor feeding and slow growth) followed by hyperphagia (increased appetite). After observing that the changes in appetite and weight gain which occur in PWS are more gradual and complex than traditionally described, a research team investigated and presented an updated clinical description of the nutritional phases of PWS. Their research was published in 2011 outlining 5 major phases, including some sub-phases. These are summarised below, but for a more detailed description of each phase, please see TABLE I. Clinical Characteristics of the Nutritional Phases

Phase     Ages                                 Characteristics

0             prenatal-birth                 Decreased fetal movements and lower birth weight than siblings

1a           0-9 months                      Hypotonia with difficulty feeding and decreased appetite

1b           9-25 months                    Improved feeding and appetite; growing appropriately

2a           2.1-4.5 years                    Weight increasing without appetite increase or excess calories

2b           4.5 – 8 years                     Increased appetite and interest in food, but can feel full

3             8 years – adulthood        Hyperphagic; rarely feels full

4             adulthood                        Appetite is no longer insatiable (only very few adults and usually > 30 years)

Miller JL, Lynn CH, Driscoll DC, Goldstone AP, Gold J-A, Kimonis V, Dykens E, Butler MG, Shuster JJ, Driscoll DJ. (2011). Nutritional phases in Prader–Willi syndrome. Am J Med Genet Part A 155:1040–1049

The neurological and endocrine mechanisms underlying the progression of these phases remains unclear, but awareness of the various phases can aid both parents and researchers. Parents will know what to expect as their child grows which can help prevent early-onset obesity and researchers are able to study the biological mechanisms of each phase, providing a basis for developing new treatments.