pre/neonatal genetic testing

types of screening

• invasive prenatal diagnosis

• non-invasive prenatal screening/diagnosis

• newborn screening

invasive prenatal diagnosis

• amnio

• CVS

• PGD

non-invasive prenatal screening/diagnosis

• ultrasonography

• serum

• etc

amniocentesis

amniotic fluid (containing fetal cells) extracted transabdominally at 16-20 weeks

• DNA/chromosomes can be examined

• levels of alpha-fetoprotein (AFP) can be determined

levels of alpha-fetoprotein (AFP) can be determined by amniocentesis

levels will be high if there is a neural tube defect

• also calls by twinning, fetal death, false-positives if gestational age undetermined, other fetal abnormalities

amniocentesis complications

1/400 miscarry (above baseline) if 16-20 weeks

• not advised in younger embryos (clubfeet, amniotic fluid leakage, spontaneous abortion)

chorion

derives from the trophoblast

chorionic villus sampling (CVS)

transcervical or transabdominal collection

• done between 10-13th week

• no ability to detect AFP levels

chorionic villus sampling complications

• about the same genetic risk as amnio

• early reports of fetal limb loss

pre-implantation genetic diagnosis (PGD)

• allows for selection of embryos before IVF

• blastomere biopsy or blastocyst biopsy

• implant genetically sound embryo, discard the rest

PGD: blastomere biopsy

8-16 cells

• pre-compaction

PGD: blastocyst biopsy

removal of a few cells of trophoectoderm

ultrasonography

• looking for structural fetal anomalies

• determine fetal sex (>13 weeks)

maternal serum 1st trimester

• pregnancy associated plasma protein A (PAPP-A): lower in trisomies

• human chorionic gonadotropin (hCG): changed in trisomies

maternal serum 2nd trimester

• unconjugated estriol: lower in trisomies

• inhibin A: changed in trisomies

cell free fetal DNA

• 2-10% of cell-free DNA in maternal blood is from placental trophoblasts

• high throughout sequencing

down syndrome CVS/amnio screening

karyotype from material and look for trisomy 21

down syndrome maternal serum screening

• PAPP-A low

• HCG elevated

• inhibitin A elevated

• unconjugated estriol low

down syndrome ultrasonography screening

widened nuchal translucency

1960s newborn screening

• test developed for PKU

• established how to store blood on filter paper

2002 newborn screening

expanded testing (most states only tested for 4-6 disorders)

• 29 core tests

• 25 secondary tests- no known treatment/etiology

2011 newborn screening

all states test for at least 26 disorders

newborn screening now

participation is at least 99.9% across US and Puerto Rico

• 1/300 infants is diagnosed with one of these disorders via newborn screening

requirements to be part of newborn panel

• the condition can be identified 24-48 hours after birth, when it cannot usually be detected by a doctor’s exam

• test is specific and sensitive for the condition

• early detection, timely intervention, and effective treatment offer proven benefit

IUGR major phenotypic features

• age at onset: prenatal

• intrauterine growth restriction

• increased nuchal fold

• dysmorphic facies

IUGR

Intrauterine growth restriction (IUGR) is diagnosed when a fetus or neonate is less than 10th percentile for weight (<2500 g for a neonate born at term in the United States)

IUGR vs SGA

A newborn with IUGR should be distinguished from a newborn who is small for gestational age (SGA) who is also below the 10th percentile in size but is small for physiological reasons, such as the size of the parents.

• Approximately 7% of pregnancies result in a fetus who is SGA, of which approximately 1 in 8 is truly IUGR.

possible causes of IUGR

• uteroplacental insufficiency,

• exposure to drugs or alcohol,

• congenital infections, or

• intrinsic genetic limitations of growth potential.

Fetuses with growth restriction due to nutritional compromise

tend to have less retardation of head growth compared to the rest of the body.

IUGR chromosomal disorders

Several chromosomal disorders are associated with IUGR, and a finding of early or symmetrical IUGR increases the likelihood that a fetus is affected with a chromosomal abnormality such as

• trisomy 18,

• triploidy, or

• maternal uniparental disomy for chromosome 7 or 14.

IUGR nuchal fold measurements

Nuchal fold measurements of more than 3 mm in the first trimester (11 to 14 weeks) and of 6 mm or more in the second trimester are considered increased and are associated with a greater risk for Down syndrome.

• Approximately one in seven fetuses with a second-trimester nuchal thickening will have Down syndrome. The ultrasound findings in A.G.'s fetus increased the suspicion of aneuploidy and led to the identification of the small interstitial deletion in 4p, which is the likely explanation for the fetal abnormalities.

IUGR ultrasound findings

The ultrasound findings in A.G.'s fetus increased the suspicion of aneuploidy and led to the identification of the small interstitial deletion in 4p, which is the likely explanation for the fetal abnormalities.

IUGR etiology

The etiology and incidence of such a rare deletion are not entirely understood, especially in light of the normal parental chromosomes.

IUGR: gonadal mosaicism

Most de novo deletions are considered to originate at meiosis, but they may also arise during mitosis, before meiosis in gametogenesis, so that a parent is a gonadal mosaic.

• Gonadal mosaicism cannot be ruled out with any certainty by fibroblast or lymphoblast testing of the parents; consequently, prenatal testing should be offered in future pregnancies.

IUGR DNA difference

The deletion breakpoints on the short arm of chromosome 4 in 46,XX,del(4)(p15.1p15.32) flank a 14.5-Mb segment of DNA. Analysis of the human genome sequence in this region indicates that 47 known protein-coding genes exist within this deleted region; haploinsufficiency for one or more of these genes is the likely cause of the phenotype of this fetus.

IUGR: chromosome microarray testing

Chromosome microarray testing allows more precise definition of breakpoints in deletions or duplications than does prenatal karyotype, thus determining which genes are involved in the deleted area.

• This may add more precise prognostic information if the involvement of critical genes is in question.

all pregnancies risk

All pregnancies regardless of family, medical, or pregnancy history are at an approximate 3% to 5% risk for developmental disabilities or a birth defect in the infant.

IUGR second trimester ultrasound

Although this couple was not at increased risk, the routine second-trimester ultrasound findings increased the suspicion of fetal aneuploidy. The finding of an interstitial deletion is likely to explain the ultrasound findings.

Although this exact deletion had not been reported previously, many deletions of the short arm of chromosome 4 have been associated with birth defects. For example:

Wolf-Hirschhorn syndrome is due to a microdeletion of 4p, resulting in both severe intellectual disabilities and physical anomalies.

FISH analysis in IUGR case study

FISH analysis in this fetus revealed that the sequences for the Wolf-Hirschhorn critical region at 4p16.3 were present on both copies of chromosome 4 and that the deletion in this case was more proximal, in band p15.

FISH outcome in the case study

In this case, as with any substantial loss or gain of material on an autosome not previously reported in other patients, the outcome is likely to involve both physical and neurological impairment, the severity of which cannot be predicted.

treatment

No curative treatments are available for chromosome abnormalities.

• The overriding question for many couples regarding the outcome for their unborn child is whether the fetus is at risk for intellectual disability or a significant birth defect.

options for IUGR

In light of the already present ultrasound anomalies and the identified chromosomal abnormality, this fetus will have sequelae, the extent of which is not predictable.

• In such cases, the couple is counseled in detail about the limited information and the inability to conclude with any certainty about the expected outcome of the pregnancy.

• The options include continuation of the pregnancy with expectant management, with or without giving the neonate up for adoption, or termination of pregnancy.

Follow-up ultrasound evaluations

can assess fetal growth and development.

• Long-term progressive IUGR alone suggests a poor prognosis for the fetus.

IUGR: late second trimester

By the late second trimester, the majority of cardiac lesions that would require intervention at birth can usually be identified.

IUGR: delivery

Consultation with neonatologists and maternal-fetal medicine specialists can provide information regarding what to expect at delivery and the types of postnatal evaluations that should be considered. There may be advantages to arranging for delivery in a tertiary facility that provides specialized neonatal intensive care and surgery.

pregnancy termination

currently legal in the United States, but not always available.

• In the second trimester of pregnancy, this procedure can be performed by either dilation and evacuation or induction of labor (prostaglandin induction).

dilation and evacuation

usually not performed in pregnancies of more than 24 weeks' gestation.

prostaglandin induction

Prostaglandin induction provides the couple with the option of an autopsy, but with a known serious chromosome anomaly, the information from an autopsy provides no additional information that would affect recurrence risk or prenatal testing options in a future pregnancy.

types of termination: discussion w pt

The emotional and physical benefits and disadvantages of the two procedures should be outlined in detail before the patient's decision to terminate, should that option be chosen.

pregnancy termination costs

In the majority of states in the U.S., pregnancy terminations are not covered by private health insurance, even when the indication is for a severe birth defect diagnosed prenatally.

• The costs can be in excess of thousands of dollars, and the financial burden of this procedure may affect decision making in some individuals.

adoption

Finally, the parents can be offered the option of giving the neonate up for adoption if they decide that termination is either not an option or unaffordable, or because the anomalies were identified too late in the pregnancy to allow termination.

inheritance risk

De novo deletions have a low recurrence risk, due to the chance of undetectable gonadal mosaicism in either parent.

• Prenatal testing, such as chorionic villus sampling or amniocentesis, is available for future pregnancies, although the risk for miscarriage from these procedures may be comparable to the actual empirical risk for a recurrence.