Table 1.

A comparison of the different mutations and the effects on the imprinted and non-imprinted genes in the Prader-Willi and Angelman syndromes. Note that while loss-of-function mutations for UBE3A show the full phenotype of Angelman syndrome, no single gene mutation has been shown to reproduce the full phenotype of Prader-Willi syndrome.

	Deletion	Uniparental disomy	Imprinting defect	Loss-of-function mutations
PWS
Frequency	65%–75% of affected individuals5	20%–30% of affected individuals5	1%–3% of affected individuals5	Not applicable
Effect on imprinted genes	No expression of paternally expressed genes in the 15q11-q13 chromosome region5	No expression of paternally expressed genes in the 15q11-q13 chromosome region, predicted increases in dosage for maternally expressed genes5	No expression of paternally expressed genes in the 15q11-q13 chromosome region, predicted increases in dosage for maternally expressed genes5	Not applicable
Effect on non-imprinted genes	One copy of the GABRB3, GABRB5, GABRG3, OCA2 and HERC2 genes, additional loss of TUBGC5, CYFIP1, NIPA1 and NIPA2 in Class I deletions5	None	None	Not applicable
AS
Frequency	~70% of affected individuals9	~2% of affected individuals9	~2%–3% of affected individuals9	~25% of affected individuals9
Effect on imprinted genes	No expression of UBE3A in neurons10	No expression of UBE3A in neurons10	No expression of UBE3A in neurons10	No expression of UBE3A in neurons10
Effect on non-imprinted genes	One copy of the GABRB3, GABRB5, GABRG3, OCA2 and HERC2 genes, additional loss of TUBGC5, CYFIP1, NIPA1 and NIPA2 in Class I deletions5	None	None	None

PWS: Prader–Willi syndrome; AS: Angelman syndrome.