Risk for the sibs of a proband
If a mutation of JAG1 is present, prenatal genetic testing is available, and testing of the parents will allow to determine whether the mutation is transmitted or de novo.
If the mutation is transmitted, the risk in sibs is 50%. If the mutation is de novo, the risk for sibs is not null because of possible germline mosaicism (estimated to be 8% in a series) but no figure could be precise.
If there is no mutation, clinical examination of the parents including liver function tests, cardiac evaluation, chest radiograph, and ophthalmologic examination must be undertaken. The presence of AGS peculiar facies in the parents must be considered with caution if isolated.
If one parent is considered as affected, the risk for sibs is 50%.
If there is no affected parent, determined through genetic counseling as mentioned above, the risk for sibs is not null but difficult to assess.
Risk for offspring of a proband
The offspring of an AGS patient has a 50% chance of inheriting the syndrome.
Prenatal molecular testing, if available, can be performed on cells obtained by chorionic villous sampling at 10-12 weeks of gestation or amniocentesis at 16-18 weeks of gestation.
Fetal ultrasound examination may show cardiac defects and kidney abnormalities.
In all cases, due to high variable expressivity, it is impossible to predict the number and the severity of the features in affected sib or offspring of a proband.
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