1p36 deletion syndrome associated with Prader-Willi-like phenotype

1p36 deletion syndrome is one of the most common subtelomeric deletion syndromes, characterized by moderate to severe mental retardation, characteristic facial appearance, hypotonia, obesity, and seizures. The clinical features often overlap with those of Prader-Willi syndrome (PWS). To elucidate the phenotype-genotype correlation in 1p36 deletion syndrome, two cases involving a PWS-like phenotype were analyzed on molecular cytogenetics.

Two patients presenting with the PWS-like phenotype but having negative results for PWS underwent fluorescence in situ hybridization (FISH). The size of the chromosome 1p36 deletions was characterized using probes of BAC clones based on the University of California, Santa Cruz (UCSC) Genome Browser.

PWS was excluded on FISH and methylation-specific polymerase chain reaction. Subsequent FISH using the probe D1Z2 showed deletion of the 1p36.3 region, confirming the diagnosis of 1p36 deletion syndrome. Further analysis characterized the 1p36 deletions as being located between 4.17 and 4.36 Mb in patient 1 and between 4.89 and 6.09 Mb in patient 2.

Patients with 1p36 deletion syndrome exhibit a PWS-like phenotype and are therefore probably underdiagnosed. The possible involvement of the terminal 4 Mb region of chromosome 1p36 in the PWS-like phenotype is hypothesized.