De Novo Mutations: New mutation not present in either parent. Important because negative family history does NOT rule out genetic disease. Examples: achondroplasia (85% de novo FGFR3), some BRCA variants, Turner syndrome.
Inheritance Patterns
Pattern
Key Features
Recurrence Risk
Examples
Autosomal Dominant
Affected in every generation; male & female equally; one affected parent usually present
Maternal inheritance only; affects both sexes but passed only via mother; variable expression (heteroplasmy)
Variable — all children of affected mother at risk
MELAS, Leber's optic neuropathy, MERRF
Penetrance vs Expressivity:Penetrance = proportion of people with the genotype who show any phenotype (e.g., BRCA1 has ~70% lifetime breast cancer penetrance). Expressivity = degree to which phenotype is expressed among those who show it (e.g., neurofibromatosis varies from a few spots to severe disease). Reduced penetrance can make a condition appear to "skip" generations mimicking recessive inheritance.
Pedigree Drawing Conventions
Standard Symbols
Circle = female; Square = male; Diamond = unknown sex
Sub-microscopic copy number variants (CNVs) genome-wide
Developmental delay/autism/dysmorphic features with normal karyotype
Sanger Sequencing
Single gene mutation confirmation
Known familial variant confirmation; targeted testing
NGS / Gene Panel
Multiple genes simultaneously for point mutations & small indels
Hereditary cancer panels (BRCA1/2 + others); cardiomyopathy panels
Whole Exome/Genome (WES/WGS)
All coding sequences (exome) or entire genome
Undiagnosed rare disease; research
NIPT (cfDNA)
Fetal chromosomal aneuploidy from maternal blood
Prenatal screening T21/T18/T13; high sensitivity; confirmatory karyotype needed
Consanguinity & GCC Context
Consanguinity — Definition & Genetics
Coefficient of Relationship (r)
First cousins: r = 1/8 → coefficient of inbreeding F = 1/16 (6.25%)
First cousins once removed: F = 1/32
Second cousins: F = 1/64
Uncle–niece or aunt–nephew: F = 1/8
Key Principle: Consanguinity does NOT create new mutations — it increases the probability that both parents carry the SAME recessive allele inherited from a common ancestor, thus dramatically raising the risk of autosomal recessive disease in offspring.
Risk Calculation
For a general AR condition with population carrier frequency q:
Non-consanguineous couple: Risk of AR child = q² (Hardy-Weinberg)
First-cousin couple: Risk = q² + Fq(1-q) ≈ substantially elevated when q is small
For rare conditions, consanguinity can increase risk 5–10 fold over background.
GCC Consanguinity Rates
UAE: ~40–50% of marriages consanguineous
Saudi Arabia: ~50–60%
Qatar: ~45–55%
Kuwait: ~40–50%
Global average: ~10–15%
Common Autosomal Recessive Conditions in GCC
Condition
Gene/Locus
GCC Prevalence
Key Feature
Sickle Cell Disease
HBB (Glu6Val)
Carrier rate up to 25% in some Gulf populations
Haemolytic anaemia, vaso-occlusive crises, organ damage
Beta-Thalassaemia
HBB mutations
Carrier 3–9% across GCC; higher in Eastern Province (Saudi)
Transfusion-dependent severe anaemia; iron overload
G6PD Deficiency
G6PD (X-linked)
5–25% males in GCC countries
Haemolytic anaemia triggered by oxidants, neonatal jaundice
PKU (Phenylketonuria)
PAH
1:4,000–1:10,000; elevated in consanguineous populations
Intellectual disability if untreated; low-phe diet essential
Nursing Role in Premarital Screening: Explain the purpose of testing (not to prevent marriage but to allow informed decision-making). Maintain confidentiality. Provide non-directive counselling — couples have the right to proceed with marriage even if both carry the same gene. Document consent. Refer to clinical genetics if results are complex. Provide written information in Arabic where possible.
Genetic Counselling Principles
Core Principles (NSGC Framework)
Non-directive: Counsellor presents information; patient/family makes own decisions
Autonomy: Respect patient's right to choose (including to not know)
Beneficence: Act in the patient's best interest
Non-maleficence: Avoid harm from disclosure or testing
Justice: Equal access to genetic services
Confidentiality: Results are private; complex tension with duty to warn relatives
Carrier Screening
Carrier screening identifies individuals who carry one copy of an AR gene variant. Carriers are unaffected but can pass the variant to offspring. When both parents are carriers, each pregnancy has a 25% chance of the condition.
Cascade Screening
After identifying an index case, systematic testing of biological relatives to find other carriers or affected individuals. Most cost-effective approach for conditions like familial hypercholesterolaemia, BRCA mutations, and hereditary haemoglobinopathies.
Common Genetic Conditions in GCC
Type
Genotype
Clinical Severity
Management
Alpha Thal Trait
-α/αα
Silent carrier; normal CBC
Genetic counselling
Alpha Thal Minor
--/αα or -α/-α
Mild microcytic anaemia; often misdiagnosed as iron-deficiency
EMERGENCY — ACS: New infiltrate on CXR + fever/respiratory symptoms. Most common cause of death in SCD adults. Treat: O₂, incentive spirometry, exchange transfusion, bronchodilators, antibiotics. Avoid fluid overload.
Stroke Prevention
TCD (transcranial Doppler) screening from age 2 annually
PCSK9 inhibitors (evolocumab/alirocumab) if LDL target not reached
LDL apheresis for homozygous FH
Lomitapide/inclisiran — newer agents
Target: >50% LDL reduction from baseline; LDL <1.8 mmol/L if high-risk CVD
Cascade Screening
Once a proband is identified, screen all first-degree relatives. Childhood screening from age 5–10 if parent has FH. Cost-effective and potentially life-saving as untreated HeFH carries 20× increased CAD risk.
Cancer Genetics
NICE NG151 Criteria — Offer BRCA Testing If:
Personal history of breast cancer + ANY of: diagnosed ≤40 years; bilateral breast cancer; triple-negative breast cancer ≤60yr; Jewish ancestry
Ovarian/fallopian tube/primary peritoneal cancer at any age
Male breast cancer
Family history score: Manchester or equivalent scoring ≥15% BRCA probability
Known family BRCA mutation — offer predictive testing
Pancreatic cancer + 1 close relative with breast/ovarian/pancreatic cancer
BRCA1 vs BRCA2 Cancer Risks (Lifetime)
Cancer
BRCA1
BRCA2
Female breast cancer
~70%
~70%
Ovarian cancer
~44%
~17%
Male breast cancer
~1–2%
~6–8%
Pancreatic cancer
Slight increase
~5%
Prostate cancer
Slight increase
~20% (aggressive)
Risk-Reducing Options for BRCA Carriers: Enhanced surveillance (annual MRI from age 25–30; mammogram from 30–40); Risk-reducing mastectomy (~95% risk reduction); Risk-reducing bilateral salpingo-oophorectomy (>90% ovarian cancer risk reduction — recommended by 35–40 for BRCA1, 40–45 for BRCA2); Chemoprevention (tamoxifen/raloxifene/anastrozole).
Loss of MMR function → microsatellite instability (MSI)
CRC risk: 40–70% lifetime (MLH1/MSH2 highest)
Endometrial cancer: 40–60% (MLH1/MSH2)
Also: ovarian, gastric, urinary tract, small bowel, brain (Turcot variant)
Amsterdam Criteria II
3–2–1 rule: ≥3 relatives with Lynch-associated cancer (one = first-degree relative of the other two); ≥2 successive generations; ≥1 case diagnosed <50 years; FAP excluded; tumours verified by pathology.
Universal Tumour Testing
All colorectal and endometrial cancers should undergo reflex MSI/IHC testing for MMR proteins. Loss of a specific MMR protein on IHC directs germline testing:
Loss of MLH1/PMS2: BRAF V600E / MLH1 promoter methylation first (somatic); if negative → germline MLH1 testing
Loss of MSH2/MSH6: directly to germline MSH2/MSH6/EPCAM
Surveillance
Colonoscopy every 1–2 years from age 25 (or 2–5yr before youngest affected relative)
Endometrial sampling/TVU annually from age 35 (consider RRSO after childbearing)
Aspirin 600mg/day reduces CRC risk in Lynch (CAPP2 trial)
Familial Adenomatous Polyposis (FAP)
Genetics
Autosomal dominant — APC gene (chromosome 5q22)
Hundreds to thousands of colorectal polyps developing in teens/20s
Near 100% risk of CRC by age 40 if untreated
Attenuated FAP (AFAP): fewer polyps (<100), later onset
Desmoid tumours (more common if APC mutation codon 1310–2000)
Osteomas (jaw); epidermoid cysts; CHRPE (congenital hypertrophy of RPE)
Gardner syndrome (FAP + soft tissue tumours)
Turcot syndrome (FAP + medulloblastoma)
Management
Annual flexible sigmoidoscopy/colonoscopy from age 12–14
Prophylactic colectomy recommended by late teens/early 20s (or when polyps >20 or high-grade dysplasia)
Options: proctocolectomy + IPAA (ileal pouch) or subtotal colectomy + IRA
Upper GI endoscopy every 1–5 years (Spigelman stage-dependent)
Li-Fraumeni Syndrome & Pre/Post-Test Counselling
Li-Fraumeni Syndrome
Autosomal dominant — TP53 gene ("guardian of the genome")
Childhood-onset sarcomas, adrenocortical carcinoma, brain tumours, breast cancer <30yr, leukaemia
~90% lifetime cancer risk
Whole-body MRI annually (Toronto Protocol)
Avoid radiation-based imaging/treatment where possible
Consider testing all close relatives if confirmed
Genetic Counselling: Pre & Post-Test
Pre-Test Counselling Must Include:
Purpose, nature and limitations of the test
Possible results (positive / negative / variant of uncertain significance — VUS)
Implications for patient and relatives
Emotional/psychological impact
Insurance and employment implications (discuss with patient)
Right to decline testing (autonomy)
Written information provided
Post-Test Counselling: Explain results in plain language. Provide written summary. Discuss surveillance/management options. Offer referral to clinical psychology. Address duty to warn family members — this is an ethical tension (see Tab 5).
Genomic Nursing Practice
Taking a Three-Generation Family History
Structure
Start with the proband (patient)
Ask about parents, siblings, children (first-degree relatives)
Ask about grandparents, aunts/uncles, cousins (second/third degree)
Record: age, health status, cause of death, age at diagnosis
Use standard pedigree notation (see Tab 1). Document in medical record. Flag to genetics team if red flags present.
Red Flags Requiring Genetics Referral
Cancer diagnosed at unusually young age (<50yr)
Multiple primary cancers in one individual
Bilateral cancers (both breasts, both kidneys)
Rare tumour type (adrenocortical carcinoma, male breast cancer)
Multiple affected family members with same or related cancers
Multiple congenital abnormalities in a child
Unexplained intellectual disability + dysmorphic features
Consanguineous parents + sick child
Recurrent pregnancy loss ≥3
Ethnic background with high-frequency recessive conditions
Informed Consent for Genetic Testing
Genetic testing requires enhanced consent beyond standard clinical consent due to the following unique features:
Unique Features of Genetic Information
Results have implications for blood relatives (not just patient)
Reveals permanent, immutable information about self
May reveal unexpected findings (misattributed paternity, unsuspected conditions)
Variants of Uncertain Significance (VUS) create ambiguity
Insurance/employment risk in some jurisdictions
Psychological impact can be significant
Consent Documentation Must Include
Nature of the test and what it can/cannot detect
Who will have access to results
How results will be communicated
Right to withdraw consent before analysis
Storage and future use of DNA/samples
Incidental findings policy — does the lab report unexpected findings?
Right NOT to know: Patients have the right to decline knowing their genetic test results or decline testing altogether. This must be respected even if results would benefit the patient clinically.
Duty to Warn Relatives — Ethical Tensions
The Ethical Conflict
When a patient carries a pathogenic variant (e.g., BRCA1, Lynch syndrome, Huntington's), close relatives may be at 50% risk. Should the nurse/genetics team breach confidentiality to warn them?
Competing Principles:
Confidentiality (patient): Patient may refuse to tell relatives
Beneficence (relatives): Relatives could benefit from testing and surveillance
Autonomy (relatives): Relatives have a right to know/right not to know
Professional Guidance (UK/International)
Recommended approach:
Explore reasons for non-disclosure with patient
Discuss benefits of family communication; offer to write letters for patient to share
Document discussions clearly
Seek ethics committee/clinical genetics input if patient refuses and relatives face serious harm
In GCC context: family-centred culture may support disclosure but patient consent still paramount
Breach of confidentiality justified ONLY if: serious harm is imminent, disclosure limited to minimum necessary, and all other means exhausted
Pharmacogenomics — CYP450 Polymorphisms
CYP2D6 — Codeine / Opioid Metabolism
Metaboliser Type
CYP2D6 Activity
Clinical Effect with Codeine
Poor Metaboliser (PM)
None
No conversion to morphine — no analgesia
Intermediate Metaboliser (IM)
Reduced
Reduced effect
Normal/Extensive (EM)
Normal
Standard effect
Ultra-Rapid Metaboliser (UM)
Very high
TOXIC morphine levels — respiratory depression, death
EXAM ALERT: CYP2D6 ultra-rapid metabolisers given codeine (including via breast milk) can develop fatal morphine toxicity. MHRA/FDA contraindicated codeine in breastfeeding mothers and children <12 yr due to this risk.
Taken at day 5 of life (day 5–8). Heel prick onto filter paper card.
GCC Newborn Screening Expansions
UAE/Saudi/Qatar: expanded panels typically include 20–50 conditions
G6PD — mandatory in UAE, Oman, Saudi; critical in GCC due to high prevalence
Congenital adrenal hyperplasia (17-OHP)
Biotinidase deficiency
Galactosaemia
Amino acid disorders (tandem MS)
Fatty acid oxidation disorders
Hearing screen (OAE/AABR) — separate but same newborn period
Nursing Role: Explain purpose/procedure to parents. Obtain consent. Correct timing (day 5). Label accurately. Ensure follow-up if screen positive. Positive screen = recall for diagnostic testing, not diagnosis itself.
GCC Exam Prep — MCQ Practice
Practice questions aligned with DHA, DOH, SCFHS, and QCHP examination style. Click "Show Answer" to reveal the explanation.
Interactive: Inheritance Pattern Identifier
Select the features observed in the pedigree:
Genetics MCQ Bank
1. A 28-year-old Emirati woman is found to be a carrier of the HBB sickle cell mutation during premarital screening. Her partner is also found to be a carrier. What is the probability that their first child will have sickle cell disease?
A. 100%
B. 75%
C. 50%
D. 25%
Correct: D — 25% When both parents are carriers (Aa × Aa), the offspring probability is: 25% AA (unaffected), 50% Aa (carrier), 25% aa (affected). This is classic autosomal recessive inheritance. UAE's mandatory premarital screening exists precisely to identify these couples and provide genetic counselling before marriage.
2. A 3-day-old male neonate in a Dubai hospital develops severe jaundice (bilirubin 380 μmol/L). His mother consumed fava bean stew during the third trimester. The most likely diagnosis is:
A. ABO incompatibility
B. Physiological jaundice
C. G6PD deficiency haemolytic jaundice
D. Biliary atresia
Correct: C — G6PD deficiency haemolytic jaundice G6PD deficiency is prevalent in GCC (up to 25% of males). Fava beans contain vicine and convicine — oxidants that trigger haemolysis in G6PD-deficient individuals. These can cross the placenta and transfer via breast milk. The severity and timing (day 3) are characteristic of G6PD haemolytic jaundice. Management: phototherapy urgently, exchange transfusion if rising despite phototherapy, avoid oxidant triggers, educate family. Part of UAE/Saudi mandatory newborn screening.
3. A pedigree shows that all affected individuals in three generations are female, and ALL children of an affected mother (both sons and daughters) show the condition. The father of affected individuals is always unaffected. This pattern most strongly suggests:
A. Autosomal dominant inheritance
B. X-linked dominant inheritance
C. Mitochondrial inheritance
D. Autosomal recessive inheritance
Correct: C — Mitochondrial inheritance Key feature: ALL children of an affected MOTHER are at risk (or affected) regardless of sex, but the condition is NEVER passed by an affected father — this is the hallmark of mitochondrial (maternal) inheritance. Mitochondria are inherited entirely from the oocyte, not from sperm. Examples: MELAS, MERRF, Leber's hereditary optic neuropathy. Note: X-linked dominant also affects daughters of affected fathers — not seen here — making mitochondrial the correct answer.
4. A Saudi nurse is caring for a 14-year-old with beta-thalassaemia major who is on a regular transfusion programme. Her serum ferritin is 3,500 ng/mL. Which nursing intervention is the PRIORITY?
A. Administer iron supplements to correct anaemia
B. Administer iron chelation therapy as prescribed
C. Increase transfusion frequency
D. Prepare for bone marrow biopsy
Correct: B — Iron chelation therapy In transfusion-dependent thalassaemia, each unit of blood deposits ~200–250mg iron. With no physiological iron excretion mechanism, iron accumulates in the heart, liver, and endocrine organs causing cardiomyopathy, hepatic fibrosis, and endocrinopathy. Target ferritin <1,000 ng/mL. Chelation agents: Desferrioxamine (DFO — SC infusion), Deferasirox (oral), Deferiprone (oral). Iron supplements (option A) are CONTRAINDICATED — they would worsen iron overload. HSCT (not BMBx) is the curative option.
5. A 35-year-old woman with a known BRCA1 pathogenic variant attends for pre-test counselling for her 25-year-old sister. What is the probability that the sister also carries the BRCA1 variant?
A. 100%
B. 75%
C. 50%
D. 25%
Correct: C — 50% BRCA1/2 mutations follow autosomal dominant inheritance. A parent who carries a BRCA1 mutation will pass it to 50% of their offspring. Siblings share 50% of their genes (first-degree relatives). Therefore, the sister has a 50% prior probability of having inherited the same BRCA1 variant — this is reduced to near certainty (positive) or near zero (negative) once genetic testing is completed. This is the rationale for cascade screening of first-degree relatives.
6. A patient is prescribed codeine 30mg for post-operative pain. 2 hours later, his respiratory rate drops to 8/minute and he becomes difficult to rouse. Which pharmacogenomic explanation is MOST likely?
A. CYP2D6 poor metaboliser — codeine not converted to morphine
B. CYP2D6 ultra-rapid metaboliser — excessive morphine production
C. CYP2C9 poor metaboliser — reduced drug clearance
D. TPMT deficiency — myelosuppression
Correct: B — CYP2D6 ultra-rapid metaboliser Codeine is a prodrug metabolised by CYP2D6 to morphine. Ultra-rapid metabolisers (1–2% Caucasian, up to 10–29% in some North African/Arabian populations) rapidly convert large amounts of codeine to morphine, causing respiratory depression and potential death. Management: NALOXONE immediately; support ventilation; avoid codeine and tramadol in known UMs. This is a black-box warning: codeine contraindicated in children <12yr and breastfeeding mothers. CYP2D6 UM prevalence is important in GCC nursing practice.
7. In a Qatari family with a child diagnosed with phenylketonuria (PKU), which statement about the inheritance pattern and carrier status is CORRECT?
A. The parents must both be affected with PKU to produce an affected child
B. Both parents are obligate carriers; they each have a 25% chance of an affected child with each pregnancy
C. Only the mother passes PKU to children
D. The condition is X-linked so only males are at risk
Correct: B PKU (PAH gene mutations) is autosomal recessive. For an affected child to be born, BOTH parents must carry at least one copy of the PKU mutation — making them obligate carriers. Each subsequent pregnancy has a 25% risk of PKU, 50% chance of being a carrier, and 25% chance of being unaffected non-carrier. Consanguinity (common in Qatar) significantly increases the probability of two carriers meeting. Newborn screening allows early dietary intervention (low-phenylalanine diet) preventing intellectual disability.
8. Regarding G6PD deficiency management, which of the following should a nurse instruct the patient to AVOID?
A. Paracetamol and amoxicillin
B. Primaquine, dapsone, nitrofurantoin, and fava beans
C. Metformin and lisinopril
D. Iron supplements and folic acid
Correct: B — Primaquine, dapsone, nitrofurantoin, and fava beans These are the classic oxidant triggers for G6PD haemolysis. The G6PD enzyme protects RBCs from oxidative damage by generating NADPH. Without functional G6PD, RBCs are vulnerable to oxidants. Primaquine (antimalarial) and dapsone are the most commonly tested drug triggers in licensing exams. Fava beans (ful medames) are culturally significant in the GCC/Arab world — patient education about this dietary trigger is critical. Paracetamol and amoxicillin (option A) are SAFE in G6PD deficiency.
9. Which genetic testing method is MOST appropriate to confirm a suspected diagnosis of DiGeorge syndrome (22q11.2 deletion) in a neonate with conotruncal heart defect and hypocalcaemia?
A. Standard karyotype (G-banding)
B. FISH for 22q11.2 deletion
C. Whole exome sequencing
D. Mitochondrial DNA analysis
Correct: B — FISH for 22q11.2 deletion DiGeorge/velocardiofacial syndrome is caused by a ~3Mb deletion at 22q11.2. This deletion is too small to be seen on standard karyotype (which has ~5–10Mb resolution). FISH using a probe specific for the 22q11.2 locus detects this deletion rapidly and reliably — it is the first-line test for suspected 22q11.2 deletion syndrome. Note: chromosomal microarray (CMA) would also detect this and is increasingly first-line in many centres. Whole exome sequencing would also eventually find it but is more expensive and time-consuming.
10. A nurse is providing pre-test genetic counselling for a woman considering BRCA1/2 testing. Which statement BEST reflects non-directive counselling?
A. "You should definitely have the test because early detection saves lives."
B. "I'll explain all the possible outcomes and support whatever decision you make."
C. "Since your mother had BRCA1, you must be tested immediately."
D. "If you don't test, you may be putting your children at risk."
Correct: B Non-directive counselling is a fundamental principle of genetic counselling. The counsellor's role is to provide accurate, balanced information about the test — what it can detect, possible results (positive, negative, VUS), implications for the patient and family, surveillance options, and psychological impact — and then support the patient in making their OWN autonomous decision. Options A, C, and D are all directive — they direct the patient toward a specific action rather than facilitating informed autonomous choice. Respecting the right not to know is equally important.
Quick Reference: Exam High-Yield Points
Must-Know Numbers
First cousin inbreeding coefficient: F = 1/16 (6.25%)
AR offspring risk (both carriers): 25%
AD offspring risk (one parent affected): 50%
X-linked recessive: sons of carrier mother at 50% risk
BRCA1 lifetime breast cancer risk: ~70%
Lynch syndrome CRC risk: 40–70% lifetime
HbA2 >3.5% = beta-thalassaemia trait
TCD velocity >200 cm/s = chronic transfusion in SCD
Classic GCC Exam Scenarios
Consanguineous couple + sick child → think AR condition
Fava beans + jaundice/anaemia → G6PD deficiency
Ferritin 3,500 in thalassaemia → chelation therapy (NOT iron)