Paeds · genetics-dysmorphology-and-metabolism
Genetic history, pedigree construction and inheritance patterns
Also known as Family history taking · Pedigree construction · Inheritance patterns · Mode of inheritance · Recurrence risk · Standardised pedigree nomenclature
A fellowship approach to the genetic family history: draw a standardised three-generation pedigree using National Society of Genetic Counselors nomenclature, recognise each inheritance pattern from its shape (autosomal dominant, autosomal recessive, X-linked, mitochondrial, imprinting, anticipation, multifactorial), apply the recurrence-risk arithmetic that flows from it, and counsel the family honestly and non-directively — including the confounders (variable expressivity, reduced penetrance, gonadal mosaicism, consanguinity, anticipation) that change the numbers.
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Target exams
Red flags
- Two or more close relatives with the same condition, an affected sibling, or a condition in a sex-linked distribution is a genetic pattern until proven otherwise — draw the pedigree before reaching for a single test
- An acutely unwell neonate born to consanguineous parents is an inborn error of metabolism until excluded — halt catabolism, treat presumptively, and send the metabolic and genetic work-up
- A family history of sudden unexplained death, especially in the young, raises inherited cardiac arrhythmia or cardiomyopathy and demands cardiology assessment of the relatives
- An isolated case does not exclude autosomal recessive inheritance — small families, parental mosaicism, de novo change and reduced penetrance all hide the pattern
- Worsening severity or earlier onset across generations is anticipation from trinucleotide-repeat expansion until tested (fragile X, Huntington, myotonic dystrophy)
- An affected female in an X-linked recessive family is explained by skewed X-inactivation, a manifesting carrier, or gonadal mosaicism in a parent — not by a wrong diagnosis
- Always ask directly and respectfully about consanguinity and ethnicity; a first-cousin union roughly doubles the baseline risk of a congenital or genetic disorder
Life stages
Care settings
Clinical exam formats
Board mappings
- General and Community Paediatrics
- Growth and Development
- Genetics and Metabolism
- General Paediatrics - take a genetic family history, construct a pedigree and recognise inheritance patterns
- Child Development and Behaviour - assess developmental delay within its family and genetic context
- Genetics and Metabolism - counsel families on recurrence risk and reproductive options
- Genetics 13-15
- Clinical Applications
- Long Cases
- Short Cases
- Communication Stations
- 2. Genetics: chromosomal and multi-system disorders
- 3. Principles of genetic inheritance
- 4. Professional skills and knowledge: Patient management and communication
- Foundation of Practice (FOP)
- Theory and Science (TAS)
- Applied Knowledge in Practice (AKP)
- Communication
- History
- Clinical
- General Pediatrics Content Outline - D19 Genetics (6%)
- General Pediatrics Content Outline - principles of inheritance and genetic counselling
- Medical Knowledge 1: Congenital and Genetic Disorders
- Patient Care 4: Clinical Reasoning
- Systems-Based Practice 1: Patient Safety and care coordination
- Medical Expert
- Pediatrics: Genetics and Metabolism
- Communicator - genetic counselling and risk communication
A registrar is asked to assess a three-year-old with global developmental delay and is told, almost as an afterthought, that "there is something in the family." The fellowship task is not to reach for an exome first — it is to sit down and draw the pedigree. Three generations, both parental lines, the consanguinity double-line if it applies, the uncles who died in infancy, the maternal male cousin in a wheelchair, the ethnicity, the miscarriages. From that single sheet of paper the inheritance pattern declares itself, the investigation narrows, and the recurrence risk becomes a number the family can use. The pedigree is the foundation of all of clinical genetics, and it is the skill most often skipped. [1] [2]
The pedigree in one line: take four generations where possible and D.R.A.W. the answer — Document both parental lines with ethnicity and consanguinity, Recognise the pattern from the shape (vertical = dominant, horizontal or sibship = recessive, males only with carrier females = X-linked, maternal-only = mitochondrial), Apply the recurrence-risk arithmetic (1 in 2, 1 in 4, 1 in 4 overall for X-linked), and Weigh the confounders (variable expressivity, reduced penetrance, anticipation, gonadal mosaicism, non-paternity). Hold these four moves and the counselling falls out naturally. [1] [2]
Overview & Definition
A genetic family history is the structured collection of information about disease in a child's relatives, and a pedigree is its graphical representation, drawn in standardised symbols across at least three generations. The pedigree is not a decoration for the notes — it is a clinical investigation that reorganises a vague sense that "something runs in the family" into a recognisable inheritance pattern, a recurrence risk, and a rational plan for testing and counselling. The National Society of Genetic Counselors standardised pedigree nomenclature precisely so that any clinician, anywhere, could read the same family story from the same symbols. [1] [2]
The reason the pedigree is the foundation of clinical genetics is that the inheritance pattern governs everything that follows — which test to order, what the result means, what the risk is to siblings and future children, and what reproductive options exist. An autosomal dominant family is offered a different conversation from an autosomal recessive family, and both differ from an X-linked family in which the carrier sisters face their own reproductive decisions. Recognising the pattern early prevents the common error of ordering the wrong test, or the right test on the wrong relative. [1] [6]
Inheritance patterns are conventionally grouped into Mendelian (autosomal dominant, autosomal recessive, X-linked dominant, X-linked recessive), non-Mendelian (mitochondrial or maternal, genomic imprinting and parent-of-origin effects, anticipation from trinucleotide-repeat expansion, mosaicism), and multifactorial or polygenic inheritance, with chromosomal disorders forming a parallel category. The same paediatric presentation — developmental delay, a birth defect, a metabolic decompensation — can arise from any of these, and the pedigree is the instrument that distinguishes them. [2] [7]
References10ShowHide
- [1]Bennett RL, French KS, Resta RG, Doyle DL. Standardized human pedigree nomenclature: update and assessment of the recommendations of the National Society of Genetic Counselors. J Genet Couns, 2008.PMID 18792771
- [2]Bennett RL, Steinhaus KA, Uhrich SB, et al. Recommendations for standardized human pedigree nomenclature. Pedigree Standardization Task Force of the National Society of Genetic Counselors. Am J Hum Genet, 1995.PMID 7887430
- [3]Bittles AH, Black ML. Evolution in health and medicine Sackler colloquium: Consanguinity, human evolution, and complex diseases. Proc Natl Acad Sci U S A, 2010.PMID 19805052
- [4]Bittles AH. Endogamy, consanguinity and community disease profiles. Community Genet, 2005.PMID 15767749
- [5]Shieh JT, Bittles AH, Hudgins L. Consanguinity and the risk of congenital heart disease. Am J Med Genet A, 2012.PMID 22488956
- [6]Gelb BD. 2024 ASHG presidential address: Incomplete penetrance and variable expressivity: Old concepts, new urgency. Am J Hum Genet, 2025.PMID 40054435
- [7]Butler MG. Clinical Presentation, Genetics, and Laboratory Testing with Integrated Genetic Analysis of Molecular Mechanisms in Prader-Willi and Angelman Syndromes: A Review. Int J Mol Sci, 2026.PMID 41683698
- [8]Ryan NM, Heron EA. Evidence for parent-of-origin effects in autism spectrum disorder: a narrative review. J Appl Genet, 2023.PMID 36710277
- [9]Lecoquierre F, Drouot N, Coutant S, et al. Parental germline mosaicism in genome-wide phased de novo variants: Recurrence risk assessment. PLoS Genet, 2025.PMID 40163539
- [10]Verebi C, Gravrand V, Bienvenu T, et al. A retrospective cohort study and review of the literature about germline mosaicism in Duchenne muscular dystrophy. J Genet Couns, 2025.PMID 38895972