~Genetics and Genomics in Maternal Newborn Care~
1. Core Genetics Foundations (HIGH YIELD)
Chromosomes & Genes
Humans have 46 chromosomes
22 pairs of autosomes
1 pair of sex chromosomes (XX female, XY male)
Genes are segments of DNA on chromosomes that code for proteins
Each chromosome pair contains similar genes, but small variations exist (<1%)
Key Terms to Know
Autosomal: Non-sex chromosomes (1–22)
Aneuploidy: Extra or missing chromosomes
Trisomy: Three copies of one chromosome
Monosomy: One copy of a chromosome
Homologous chromosomes: Matching chromosome pairs
Mitosis vs. Meiosis:
Errors in either → chromosomal anomalies
2. Chromosomal Anomalies
Numerical vs. Structural
Numerical anomalies (more common):
Caused by extra or missing chromosomes
Often result in:
Spontaneous abortion
Congenital anomalies
Intellectual disability
Structural anomalies:
Rearrangement of chromosome material
Types:
Deletions
Duplications
Translocations
Inversions
Ring chromosomes
Isochromosomes
Chromosome Structure
p arms = short arms
q arms = long arms
Centromere = holds arms together
Telomeres = protect chromosome ends during replication
3. Risk Factors for Aneuploidy (TESTABLE)
Clients at increased risk include:
Maternal age >35
Prior child with a trisomy
Previous spontaneous abortion or fetal demise
Smoking
High BMI
Radiation exposure
Possibly folic acid deficiency
4. Autosomal Trisomies (MEMORIZE)
Trisomy 21 – Down Syndrome
Occurs in 1 in 700–800 births
Risk increases with maternal age
~75% result in fetal loss
Median lifespan ≈ 47 years
Classic Features
Flat facial profile
Upward-slanting eyes
Short neck
Small ears
Protruding tongue
Hypotonia (poor muscle tone)
Single palmar crease
Small hands and feet
Common Complications
Congenital heart defects (50%)
AVSD, VSD, PDA, Tetralogy of Fallot
Hearing and vision problems
Sleep apnea
Feeding difficulties → aspiration risk
Poor tone
Poor suck/swallow coordination
CHD affecting oxygenation
5. Sex Chromosome Anomalies (VERY COMMON ON EXAMS)
General
Affect 1 in 400 births
More survivable than autosomal anomalies
Turner Syndrome (45,X)
Females only
Most common cause of primary amenorrhea
Features
Short stature
Webbed/wide chest
Low hairline
Ovarian failure → infertility
Lymphedema
Cardiac & renal defects
Klinefelter Syndrome (47,XXY)
Males
Tall stature
Small testes
Gynecomastia
Female-pattern hair
Infertility
Delayed puberty
↑ breast cancer risk
Triple X Syndrome (47,XXX)
Females
Tall stature
Learning disabilities
Weak muscle tone
Kidney abnormalities
Behavioral/emotional challenges
XYY Syndrome (47,XYY)
Males
Tall stature
Learning disabilities
Delayed speech/motor skills
Behavioral challenges
Generally good prognosis
6. Patterns of Inheritance
Multifactorial (Polygenic)
Involves multiple genes + environment
Examples:
Type 2 diabetes
Heart disease
Obesity
Risk is difficult to predict
Family clustering without clear pattern
Single-Gene (Unifactorial)
Autosomal Dominant
Only one mutated gene needed
Affects every generation
Examples:
Huntington disease
Marfan syndrome
Autosomal Recessive
Two mutated genes required
Parents usually asymptomatic carriers
Examples:
Cystic fibrosis
Sickle cell disease
PKU
X-Linked Disorders
No male-to-male transmission
X-Linked Dominant
Males more severely affected
Example: Fragile X syndrome
X-Linked Recessive
Mostly affects males
Females are usually carriers
Example: Hemophilia
7. Inborn Error of Metabolism: PKU (VERY TESTABLE)
Autosomal recessive
Deficiency of phenylalanine hydroxylase (PAH)
Phenylalanine builds up → brain damage
Detected via newborn screening
Treatment:
Lifelong phenylalanine-restricted diet
Early treatment prevents intellectual disability
8. Cancer & Genomics (KEY CONCEPT)
Cancer itself is not inherited
Genetic mutations that increase risk can be inherited
Most cancers occur from accumulated mutations over time
Nurse should clarify:
Genetic testing identifies risk, not certainty
9. Preconception Carrier Screening
Who Should Be Offered Screening?
All clients considering pregnancy
Reproductive partner should also be offered testing
Key Points
Carriers have the gene but no disease
Sample: blood, saliva, or cheek swab
Targeted screening: ethnicity/family history
Expanded screening: many conditions regardless of ethnicity
If Both Parents Are Carriers:
25% affected
50% carrier
25% unaffected
10. Prenatal Genetic Screening vs Diagnostic Testing
Screening = risk
Diagnostic = confirmation
First Trimester (10–13 weeks)
Cell-free fetal DNA
Screens for trisomy 21, 18, 13
No fetal risk
Nuchal translucency
Measures neck fluid
↑ thickness → aneuploidy risk
CVS
Diagnostic
Risks: bleeding, miscarriage, infection, Rh sensitization
Second Trimester
Quad screen (15–22 weeks)
AFP, hCG, estriol, inhibin-A
AFP alone
Screens for neural tube defects
Anatomy scan (18–22 weeks)
Amniocentesis
Diagnostic
Ultrasound-guided
Results in ~2 weeks
Third Trimester
No routine new tests
Can repeat:
Cell-free DNA
Ultrasound
Amniocentesis (lung maturity, infection, anemia)
11. Newborn Screening (EXAM FAVORITE)
Performed 24–48 hours after birth
Includes:
Heel-stick blood test
Hearing screen
Critical congenital heart defect (CCHD) screen
Pulse ox right hand + foot
Pass: ≥95% and <3% difference
Purpose
Early detection = early treatment
Screens, does NOT diagnose
12. Role of the Nurse (VERY IMPORTANT)
Nursing Responsibilities
Education before and after testing
Nonjudgmental support
Risk assessment and family history
Referral to genetic counseling
Emotional support during waiting/results
Clear explanation: screening ≠ diagnosis
Key Communication Principles
Honest and straightforward
Nondirective
Respect client autonomy
Report all results
Support regardless of decisions
13. Impact on the Family
Emotional stress and anxiety
Ethical, legal, and social implications (ELSI)
Financial strain
Decision-making pressure
Long-term planning needs
14. Genetic Counseling
Recommended for:
Age ≥35
History of pregnancy loss
Assisted reproduction
Prior child with genetic disorder
Known carrier status
Exposure to toxins or infections
Final Exam Pearls ✨
All clients should be offered screening
Screening ≠ diagnosis
Maternal age matters
Nurses educate, support, and refer
Client choice is central