Undetectable levels of UNCONJUGATED ESTRIOL in maternal serum have led to a diagnosis of X-LINKED ICHTHYOSIS in a male fetus.

Dannielle Ghezzi1, Khoa Lam1, Wendy Waters2, Sarah Smith2, Enzo Ranieri1, Dr Michael Metz1, Dr Janice Fletcher1, Peter Sharp3

 

1 Antenatal Screening Laboratory , Department of Biochemical Genetics, Directorate of Genetics & Molecular Pathology, SA Pathology, Women’s and Children’s Hospital, Adelaide, South Australia 5006, Australia

2 Department of Cytogenetics, Directorate of Genetics & Molecular Pathology, SA Pathology, Women’s and Children’s Hospital, Adelaide, South Australia 5006, Australia

3 Metabolic Laboratory, Department of Biochemical Genetics, Directorate of Genetics & Molecular Pathology, SA Pathology, Women’s and Children’s Hospital, Adelaide, South Australia 5006, Australia

 

The South Australian Maternal Serum Antenatal Screening (SAMSAS) laboratory provides antenatal screening to the women of South Australia, Tasmania and Northern Territory. In combination with the Nuchal Translucency (NT) scan provided between 11 weeks + 2 days (11w2d) to 14 weeks, SAMSAS tests maternal serum for biochemical markers and generates a risk of aneuploidy and/or open neural tube defects using a SAMSAS  developed ‘triple test’ algorithm.

Non-invasive Prenatal testing (NIPT) is becoming the preferred screening test for common aneuploidies in place of the biochemical ‘triple test’ screen. We present a case of a microdeletion that was identified through the biochemical testing method, which currently is undetectable by commercial aneuploidy NIPT.

Unconjugated Estriol (uE3) is a marker used in the second trimester biochemical screen. A patient aged 19 years (G1P0), showed undetectable serum levels of uE3 at 14w1d, 15w2d and 17w0d of gestation. The levels of uE3 were persistently undetectable by the Siemens Immulite2000 Immunoassay platform (LLD< 0.24nmol/L). The requested repeat analysis confirmed the low uE3 levels where metabolic studies for the exclusion of Smith-Lemli-Opitz (SLO) Syndrome were performed. SLO was exclude by testing on amniotic fluid revealing low levels of the 7-dehydrocholesterol, the precursor of cholesterol in the steroid biosynthesis pathway.

The patient was also referred for cytogenetic testing by prenatal microarray with particular concern for X-linked Ichthyosis. The microarray that was performed on amniocytes identified a male fetus with a 1.6Mb interstitial microdeletion at Xp22.31. This involved the STS gene which codes for the Steroid Sulfatase enzyme (EC 3.1.6.2); an important step in the biosynthesis of UE3 and a diagnosis of X-linked Ichthyosis was made. The mother was referred for FISH testing and was found to be a carrier of this deletion which could potentially affect future pregnancies.

This highlights the importance of a biochemical screen of maternal serum and the collaboration between testing laboratories to provide additional clinical information on a pregnancy.

 


Biography

The South Australian Maternal Serum Antenatal Screening (SAMSAS) laboratory provides antenatal screening to the women of South Australia, Tasmania and Northern Territory. In combination with the Nuchal Translucency (NT) scan provided between 11 weeks + 2 days (11w2d) to 14 weeks, SAMSAS tests maternal serum for biochemical markers and generates a risk of aneuploidy and/or open neural tube defects using a SAMSAS  developed ‘triple test’ algorithm.

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