Prader–Willi syndrome

Prader–Willi syndrome is a genetic disorder caused by loss of expression of paternally inherited genes in chromosome 15q11–q13. It commonly causes infantile hypotonia, developmental disability, and excessive appetite that can lead to obesity.

Genomic imprinting: An epigenetic process in which gene activity depends on whether an allele was inherited from the mother or father. Silencing of the paternal genes central to this syndrome results from parent-specific gene expression.
Methylation testing: A laboratory method that detects parent-specific DNA methylation patterns at imprinted loci. It can confirm the syndrome by showing the absence of the paternal imprint in 15q11–q13.
Angelman syndrome: A neurodevelopmental disorder caused by loss of maternal UBE3A expression in neurons, often involving severe speech impairment and ataxia. It involves the same chromosome region but the loss of maternal rather than paternal expression.
Neonatal hypotonia: Reduced muscle tone in a newborn, often causing poor movement and difficulty feeding. This is a characteristic early sign that often prompts genetic evaluation.
Andrea Prader: A Swiss pediatrician who helped characterize Prader–Willi syndrome. He co-authored the 1956 clinical description from which the syndrome takes its name.
15q11–q13: A region of chromosome 15 containing genes involved in Prader–Willi syndrome and Angelman syndrome. The syndrome arises when expression of paternal genes in this chromosome region is lost.
Growth hormone therapy: Treatment with recombinant human growth hormone to support growth and body composition. It can improve height, lean body mass, and physical function in affected children.
Temple syndrome: An imprinting disorder involving chromosome 14 that can cause hypotonia, feeding problems, and short stature. It can resemble early Prader–Willi syndrome while arising from a different imprinted region.
Developmental disability: Limitations in intellectual and adaptive functioning that begin during development. Learning and adaptive challenges shape educational and daily-living support needs.
Heinrich Willi: A Swiss pediatrician associated with the first clinical description of Prader–Willi syndrome. His clinical observations contributed to identifying the syndrome as a distinct condition.

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