A new mutation in the AFP gene responsible for a total absence of alpha feto-protein on second trimester maternal serum screening for Down syndrome.
Alpha feto-protein (AFP) is a major plasma protein produced by the yolk sac and the liver during the fetal period. During the second trimester of pregnancy, APF and betahCG serum concentrations are commonly used for screening Down syndrome. AFP deficiency is rare (estimated to be 1/105,000 newborns) and only one sequence alteration has previously been reported in the AFP gene. We report a new mutation in exon 5 of the AFP gene, leading to a total absence of AFP on 2nd-trimester maternal serum screening for Down syndrome, confirmed on the amniotic fluid. Despite this, fetal development and birth were normal. After PCR-amplification, the whole AFP gene was sequenced. The new mutation was a guanine to adenine transition in position 543 creating a premature stop codon in position 181. In order to search for eventual modifications of the amniotic fluid profile, proteins were separated by electrophoresis and compared with 10 normal amniotic fluids sampled at the same developmental age (18 weeks). In the amniotic fluid of our patient albumin rate was reduced whereas alpha1 and beta protein fractions were increased, suggesting that AFP deficiency may modify the distribution of protein fractions. This observation emphasizes the complex molecular mechanisms of compensation of serum protein deficiency. Studies on other families with AFP deficiency are necessary to confirm this observation.
Petit
François M
FM
Department of Biochemistry, Hormonology and Genetics, Antoine Béclère Hospital AP-HP, Université Paris Sud, Clamart, France. francois.petit@abc.aphp.fr
Hébert
Marylise
M
Picone
Olivier
O
Brisset
Sophie
S
Maurin
Marie-Laure
ML
Parisot
Frédéric
F
Capel
Liliane
L
Benattar
Clarisse
C
Sénat
Marie-Victoire
MV
Tachdjian
Gérard
G
Labrune
Philippe
P
D001483:Base Sequence; D016022:Case-Control Studies; D004314:Down Syndrome / Q000175:diagnosis / Q000378:metabolism; D005260:Female; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D011247:Pregnancy; D011262:Pregnancy Trimester, Second / Q000235:genetics*; D011296:Prenatal Diagnosis; D000509:alpha-Fetoproteins / Q000235:genetics* / Q000378:metabolism
D000509:alpha-Fetoproteins