Many performance tests used today are not reliable. Only a few discriminate between the most highly functioning individuals and individuals with good function. Thus, a new recommended battery includes unassisted single-leg stand, balance platform "foam pad, eyes closed," elbow flexion and knee extension strength (strength chair), grip strength, timed chair stands, and the 6-minute walk. These simple performance-based tests have good reliability and discrimination across the range of function and can be used in most clinical and research settings to quickly assess global functional level.

Prader-Willi syndrome (PWS) is associated with paternally derived chromosomal deletions in region 15q11-13 or with maternal disomy for chromosome 15. Therefore, loss of the expressed paternal alleles of maternally imprinted genes must be responsible for the PWS phenotype. We have mapped the gene encoding the small nuclear RNA associated polypeptide SmN (SNRPN) to human chromosome 15q12 and a processed pseudogene SNRPNP1 to chromosome region 6pter-p21. Furthermore, SNRPN was mapped to the minimal deletion interval that is critical for PWS. The fact that the mouse Snrpn gene is maternally imprinted in brain suggests that loss of the paternally derived SNRPN allele may be involved in the PWS phenotype.