Prader-Willi Syndrome (PWS)

Introduction

Prader-Willi syndrome (PWS) is characterised by severe hypotonia and feeding difficulties in early infancy, followed in later infancy or early childhood by excessive eating and gradual development of morbid obesity (unless eating is controlled by dietary restriction or behaviour modification). Motor milestones and language development are delayed. All individuals have some degree of cognitive impairment, although some will have an IQ within the normal range. A distinctive behavioural phenotype (with temper tantrums, stubbornness, manipulative behaviour, and obsessive compulsive characteristics) is common. Hypogonadism is present in both males and females, and manifests as genital hypoplasia, incomplete pubertal development, and in most, infertility. Short stature is common; characteristic facial features, strabismus, and scoliosis are often present, and non-insulin-dependent diabetes mellitus often occurs in obese individuals. Consensus diagnostic clinical criteria for PWS have been developed however confirmation of diagnosis requires genetic testing.

Prader-Willi syndrome (PWS) is usually sporadic in occurrence, and may arise from paternal deletion of 15q11-13 on chromosome 15 (~75-80% of cases); maternal uniparental disomy of chromosome 15 (~20-25% of cases) and imprinting defect (~ 1% of cases). (Ramsden et al, 2010, BMC Med. Genet., 11:70).

Referral information

We accept referrals of patients with appropriate signs and symptoms for a diagnosis of PWS.

Technical information

A methylation sensitive (SNRPN) PCR test is used to detect an abnormal pattern of methylation within the 15q11-q13 region.

Price & reporting times

NHS referrals to this service are paid for where there is an existing specialist commissioning contract for genetic testing. In other cases please contact the lab for prices.

Test Price (NHS)  Price (non- NHS) TRT (Calendar days)
Methylation sensitive (SNRPN) PCR POA POA 28
Prenatal diagnosis POA POA 3

Test validation & quality assurance - information for users

More than 99% of PWS cases (those due to a deletion, maternal uniparental disomy or an imprinting defect) are detected by the methylation sensitive PCR test. Mosaic PWS cases can appear normal using this test, however these are extremely rare.

Sample requirements

4ml EDTA blood sample

Referral guidelines

Please see our referral guidelines for more information.

OMIM Number(s) - 176270

Gene(s) - (testing involves SNRPN)

y