Prader-Will Syndrome is caused by genetic variation. A rare genetic condition, due to deletion of chromosome 15, is located at chr15q11.2.

Imprinted genes of NPAP1/C15orf2. NAPAP1 stands for Nuclear Pore Associated Protein 1.

Due to a heterozygous deletion of chromosome 15q11.2, it is likely that the person could have neuropsychiatric or neurodevelopmental problems, including delayed psychomotor development, speech delay, autism spectrum disorder, attention deficit-hyperactivity disorder, obsessive-compulsive disorder. Ref: OMIM .


Heterozygous means that the particular gene or genes are having two different alleles.


Homozygous means that the particular gene or genes are having two same alleles.

Abnormality of gene NPAP1 was associated with the following diseases.

  • Mental retardation epilepsy.
  • Prader-Willi syndrome.


The inheritance of Prader-Willi Syndrome is by Autosomal Dominance. This means, one copy of the mutated gene is enough to cause Prader-Willi Syndrome. Autosomal means non-sex chromosome, it can locate on any number of the gene. Therefore human chromosome (1-22).


  • Body height abnormality.
  • Cryptorchidism. Absence of one or two testes from the scrotum. Male infertility.
  • Deformity of male external genitalia.
  • The unique facial features in particular almond-shaped eyes.
  • Childhood obesity.

Prader-Willi Syndrome is not related to any race or ethnics.

The diagnosis of PWS is as follows: (Ref: PWS)

(1) Find the characteristics of PWS.

Infants and newborns with unexplained muscle weakness (hypotonia) and poor suck.

(2) Check any known family history

(3) Genetic testing locating the specific genetic subtype (15q11-q13 deletion, maternal disomy 15. This includes  DNA methylation tests and fluorescent in situ hybridization (FISH).

According to the Abstracts from the 53rd European Society of Human Genetics (ESHG) Conference: e-Posters. Prader-Willi syndrome also caused by novel 3-7 exons deletion of SNRPN gene.

SNRPN stands for Small Nuclear Ribonucleoprotein Polypeptide N. The location of this gene is within PWS on chromosome 15 and from the expression of the paternal allele. The disease associated with this gene is Prader-Willi Syndrome and Autism.