Ch01: Child Development & Genetics

Preparatory Mindset

Child development is the backbone of paediatrics — growth and development milestones are the "vital signs" of childhood, and every paediatric exam has at least one milestone question or OSCE station. The mindset: know the key milestones by age (the "can't walk by 18 months = assess" rule, the social smile, sitting, crawling, first words, the pincer grasp), understand the primitive reflexes and when they disappear, and recognise that motor milestones are a poor predictor of cognition — speech and language predict better. For OSCE: a developmental assessment station asks you to take a developmental history (four domains: gross motor, fine motor/vision, hearing/speech/language, social/emotional/behaviour), plot growth, and flag deviations for referral. Genetics adds the dysmorphology dimension — a child with multiple anomalies → think syndrome → karyotype/microarray.

Core Concepts

1. Why development matters

• Development = acquisition of skills across four domains: gross motor, fine motor & vision, hearing & speech & language, social & emotional & behaviour.
• Developmental screening compares the child's achievements against age limits (the age by which most children have achieved a milestone) — a child missing a milestone beyond the limit needs assessment.
• Speech/language development is a better predictor of cognitive function than motor development (motor delay correlates poorly with later IQ; speech delay correlates better).
• Early detection (e.g., hearing impairment → language) improves outcomes — screening matters.

2. Key developmental milestones (by median age)

The rule to remember: "Any child not walking by 18 months should be assessed and examined." — but note *normal late walkers exist* (many walk 12-18 months); the red flag is no independent walking at 18 months.

Other key ages: head control 4 mo, sitting 6-9 mo, first words 12 mo, two-word phrases 2 yr, sentences 3 yr.

3. Primitive reflexes and their disappearance

Persistence of primitive reflexes beyond their expected disappearance → CNS pathology (cerebral palsy, hypotonia, kernicterus).

4. Growth parameters

• Weight: doubles by ~5 months, triples by 1 year; 2-3 kg/year after.
• Length/height: ~50 cm at birth, 75 cm at 1 year, ~2× birth length by 4 years.
• Head circumference: fastest in infancy — growth of head circumference in first 2 years reflects brain growth; crossing centiles = investigate (macro/microcephaly).
• Teething: first tooth ~6 months; ~20 deciduous teeth by 2.5-3 years.
• Plot on WHO growth charts (weight/height/head circumference for age); crossing centiles downward = growth concern.

5. Developmental assessment (OSCE format)

1. History — each domain, with age-appropriate questions (birth history, hearing, vision, schooling, social interaction).
2. Examination — observe, plot growth, check for dysmorphism, neurological exam (reflexes).
3. Screening tools — ASQ (Ages & Stages), Denver II, M-CHAT (autism screen).
4. Red flags requiring referral: not walking at 18 months, no speech by 2 years, loss of skills (regression → consider autism, metabolic, neurodegenerative), asymmetric motor skills (hemiplegia), persistent primitive reflexes, no social smile by 3 months.

6. Developmental disorders (high-yield)

7. Paediatric genetics (essentials)

• Karyotype: chromosomal number/structure (trisomy 21 — Down; Turner 45,X; Klinefelter 47,XXY).
• Microarray (aCGH): microdeletions/duplications (22q11 — DiGeorge).
• Single-gene disorders: autosomal dominant (achondroplasia, NF1), recessive (CF, thalassaemia, sickle cell), X-linked (DMD, haemophilia).
• Down syndrome (trisomy 21): most common chromosomal anomaly — intellectual disability, characteristic facies (flat occiput, upslanting palpebral fissures, epicanthic folds, protruding tongue), single palmar crease, congenital heart disease (~50% — AVSD, VSD), duodenal atresia, atlantoaxial instability, early Alzheimer — screening (NT + combined test; NIPT; amniocentesis).
• Maternal age >35 increases trisomy risk; consanguinity increases recessive disorders.
• Dysmorphic child + anomalies → referral for genetic evaluation (microarray first-line).

High-Yield Points

Topic Summary

Child development is assessed across four domains (gross motor, fine motor/vision, speech/language, social/emotional) with age-limit milestones — social smile 6 wk, head control 4 mo, sitting 6-9 mo, pincer 9 mo, first words 12 mo, phrases 2 yr, sentences 3 yr. Not walking by 18 months = assess. Primitive reflexes (Moro, grasp, rooting) disappear by 3-6 months; persistence suggests CNS pathology. Growth is tracked on WHO charts (weight triples by 1 yr). Speech/language predicts cognition better than motor skills. Developmental disorders — GDD, ID, ASD (regression = red flag), CP (spastic most common), ADHD — and genetics (Down syndrome + CHD, karyotype/microarray) complete the picture.