High‐resolution cytogenetic studies in patients with Prader‐Willi syndrome

We investigated 24 patients with Prader-Willi syndrome by the high-resolution banding technique. Their history and clinical findings were also examined in some detail. Twelve had interstitial deletion of 15q;.del(15) (ql 1.2q13) in 11 cases and del(15) (ql 1.2q12) in one case. Six revealed normal karyotypes at about 500–850 bands per haploid-set level. In an additional six cases, no deletion was detected. However, we took the results as tentative, as the observed karyotypes were at the 400-bands level. During the course of this study, it was realized that a small deletion in the proximal 15q could be easily overlooked when a mitotic spread around 400-bands or less per haploid-set level was used. There was no distinct difference in the clinical features of patients with interstitial deletion and those with a normal karyotype. Two cases in the latter group lacked some of the typical features of the former group, e.g. poor fetal vigor, neonatal feeding difficulty, hypotonia, and delayed motor development.