Avick G. Mitra

Normalization of maternal serum alpha-fetoprotein levels after 23 weeks' gestation in an NPHS1 nephrotic syndrome carrier pregnancy.

Elevated maternal serum alpha-fetoprotein (MS-AFP) levels have been used for detection of fetal open neural tube defects since the 1970s (Brock et al., 1973) and they remain part of a routine prenatal screening program. Other causes of elevated MS-AFP levels include ventral wall defects, placental abnormalities, epidermolysis bullosa, and fetomaternal hemorrhage. Congenital nephrosis, such as congenital nephrotic syndrome of the Finnish type (CNF), is a rare cause of an elevated MS-AFP, but should be considered when a very high MS-AFP level is associated with an ultrasound demonstrating normal fetal anatomy. In affected CNF cases, the amniotic fluid alpha-fetoprotein (AF-AFP) will also be very high but acetylcholinesterase assay will be negative. Recent literature indicates that healthy carriers for CNF may also present with very high elevations in MS-AFP and AF-AFP values in the second trimester of pregnancy (levels overlap with affected fetuses) because of temporary dysfunction of the kidneys, but these elevations are reported to normalize sometime in the second trimester (Carrera et al., 1999; Kestilä and Järvelä, 2003). However, the exact timing of this normalization of MS-AFP and AF-AFP levels has not been previously described in detail. Knowledge of the gestational age at which this normalization occurs in unaffected carriers is important for parents living in localities where termination is illegal in the late second trimester. We describe a case that provides information regarding the timing of MS-AFP and AF-AFP normalization seen in a carrier pregnancy. In our case, the parents had to make a decision on whether or not to continue their pregnancy before the AFP levels began to normalize. This case serves to remind us that caution must be exercised to avoid making a false positive diagnosis of an affected fetus, which could lead to the unnecessary interruption of a pregnancy that would have resulted in a healthy, unaffected CNF carrier child. A nonconsanguineous couple, both 32 years of age and of German descent, were referred for genetic counseling and ultrasound evaluation during their first pregnancy with an elevated MS-AFP of 8.00 multiples of the median (MoM) drawn at 15.9weeks’ gestation. The couple reported no family history of renal disease. An ultrasound at 16.7weeks demonstrated a structurally normal fetus. A maternal serum Kleihauer–Betke was done to exclude the possibility of a large fetomaternal hemorrhage and was negative. Amniocentesis revealed a normal female karyotype and significantly elevated AF-AFP of 25.41 MoM with negative acetylcholinesterase. We counseled the couple that these results were consistent with either an affected CNF fetus or an unaffected carrier and offered sequencing of four genes causing congenital nephrosis (NPHS1, NPHS2, LAMB2, and WT1 through Athena Diagnostics, Worcester, MA, USA). The couple was also referred to a pediatric nephrologist for additional counseling regarding the health problems associated with CNF. They were also informed about available pregnancy management options, including the local legal limit for termination of up to 20weeks after conception. At this time the couple stated that they would probably elect to terminate an affected fetus. At 20.2weeks’ gestation the sequencing results revealed only one disease-associated mutation in the NPHS1 gene (1868G to T transversion) and very likely an unaffected heterozygote. This previously described mutation causes an amino acid change in the nephrin protein, a cysteine to a phenylalanine, and was later found to have been inherited from the father (Lenkkeri et al., 1999). The small possibility of a second undetectable mutation resulting in an affected fetus could not be completely ruled out (Lemley, 2006). On the basis of these reassuring results this couple elected to continue the pregnancy. To obtain additional reassurance regarding an unaffected carrier state, this couple elected serial MS-AFP testing and a second amniocentesis at 20.3 weeks to obtain another AF-AFP. Rather than observing a decrease in AFP *Correspondence to: Teresa Brady, Carolinas Medical Center — Women’s Institute, 14214 Ballantyne Lake Rd., Charlotte, NC 28277, USA. E-mail: teresa.brady@carolinashealthcare.org

Maternal serum alpha‐fetoprotein levels peak at 19–21 weeks' gestation and subsequently decline in an NPHS1 sequence variant heterozygote; implications for prenatal diagnosis of congenital nephrosis of the Finnish type

CASE REPORT Congenital nephrosis of the Finnish (CNF) type is a rare autosomal recessive disease caused by mutations in the NPHS1 gene that controls transcription of the protein nephrin. Classically, affected homozygotes have abnormal nephrin production that leads to severe neonatal proteinuria. Children with CNF have problems with malnutrition, are at increased risk for infection, and are at significant risk for end-stage renal failure. For affected individuals, proteinuria begins in utero and is manifested by significantly increased maternal serum alphafetoprotein levels (MS-AFP) throughout the second trimester of pregnancy. A fascinating and important observation first made by Mannikko et al. in 1997 and reaffirmed by Carrera et al. in 1999 is that carrier fetuses (expected to be healthy, unaffected neonates) also have similarly elevated second trimester MSAFP levels, but these values begin to normalize in the late second trimester. It was postulated by Patrakka et al. in 2002 that carrier fetuses have an initial shortage of normal nephrin protein that is necessary for proper functioning of the glomerular slit diaphragm. As the gestation advances and glomerulosis is completed, the nephrin levels are no longer critically low and thus the protein leakage begins to resolve. The exact timing of this normalization process has not been previously described. In a prior case report, our group attempted to more precisely define the peak in MS-AFP levels in a carrier fetus noting that MS-AFP levels rose through 20weeks and appeared to decline thereafter. In this report, we describe a second case in which the peak MS-AFP values most likely occurred between 19 and 21weeks’ gestation after which they steadily declined. This fetus was ultimately found to be a carrier for a NPHS1 gene sequence variant. A nonconsanguineous couple, 32 and 40years of age, presented during a second pregnancy with an elevated MS-AFP value of 12.08multiple of the median (MoM) at 19 1/7ths weeks. She was of Spanish and Italian ancestry and he was of Irish and French ancestry. Their first pregnancy was uncomplicated and resulted in a healthy son. The family history was notable for the husband reporting childhood proteinuria that resolved; he denied any ongoing renal dysfunction, and normal kidney functionwas confirmed during this pregnancy by a nephrologist. Initial ultrasound evaluation at 20 1/7ths weeks’ gestation at an outside practice revealed normal fetal anatomy. Diagnostic amniocentesis was performed at that time and yielded a normal female karyotype (46, XX) but a markedly elevated amniotic fluid alpha-fetoprotein value of 37.27MoM with negative acetylcholinesterase assay. The couple was counseled that these results were indicative of a fetus affected with CNF and an ultimately poor prognosis. The couple underwent gene sequencing for the NPHS1 gene through Athena Diagnostics, Worcester, MA, USA, and the option of termination was discussed. The patient then requested a second opinion from our practice. We counseled them that the results of their evaluation could be consistent with either an affected fetus or an unaffected carrier. We further counseled them regarding the autosomal recessive nature of this disease and discussed that the rarity of CNF in North America makes it more likely that the fetus would be an unaffected carrier. Given the possibility of a healthy baby, the couple decided to defer their decision regarding pregnancy termination until further evaluation could be completed. A referral to a pediatric nephrologist was made for further discussion and education