An 8-year-old girl is referred to the child psychiatry clinic by her school teacher for concerns about learning difficulties and behavioural problems. The child's developmental history reveals that she achieved major milestones within normal limits until age 3 years, after which her parents noticed progressive loss of purposeful hand skills, loss of language, and onset of repetitive hand-wringing movements. She now has severe intellectual disability (IQ 25), does not speak, and engages in self-injurious behaviour. On examination, she has microcephaly, spasticity in all four limbs, and hyperreflexia. EEG shows generalized spike-and-wave discharges. Brain MRI reveals cerebral atrophy and white matter changes. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Rett Syndrome ### Key Clinical Features **Key Point:** Rett syndrome is characterized by **normal development for 6–18 months, followed by progressive regression** of motor and cognitive skills, loss of purposeful hand skills, and development of stereotyped hand movements (hand-wringing, hand-mouthing). ### Diagnostic Criteria for Rett Syndrome The case presents the **classic four-stage progression** of Rett syndrome: | Stage | Age | Features | |-------|-----|----------| | **Stage I: Early infantile** | 6–18 months | Normal development, subtle decrease in growth rate, loss of interest in environment | | **Stage II: Regression** | 1–4 years | **Rapid loss of purposeful hand skills, language regression, loss of social engagement** | | **Stage III: Pseudo-stationary** | 2–10 years | Stabilization of regression, emergence of seizures, spasticity, ataxia, stereotyped hand movements | | **Stage IV: Late motor deterioration** | >10 years | Progressive spasticity, rigidity, scoliosis, loss of ambulation | **High-Yield:** The **loss of purposeful hand skills** (replaced by stereotyped hand-wringing, hand-mouthing, or clapping) is **pathognomonic** for Rett syndrome and distinguishes it from other causes of intellectual disability. ### Neurobiological Basis **Mnemonic: MECP2** — **M**ethyl-**C**pG-**b**inding **P**rotein 2 gene mutation (X-linked dominant). MECP2 encodes a protein essential for normal brain development and synaptic plasticity. Loss of function leads to: - Impaired neuronal maturation - Abnormal synaptic transmission - Progressive neurodegeneration - Seizures (75% of cases by age 10) ### Clinical Features in This Case 1. **Normal development until age 3:** Rules out congenital intellectual disability 2. **Progressive loss of purposeful hand skills:** Hallmark of Rett syndrome 3. **Loss of language:** Expressive language regression is universal 4. **Stereotyped hand movements:** Hand-wringing, hand-mouthing, clapping (occur during waking hours) 5. **Severe intellectual disability (IQ 25):** Profound regression from previously normal cognition 6. **Microcephaly:** Acquired, develops after normal head growth in infancy 7. **Spasticity and hyperreflexia:** Motor system involvement 8. **Seizures (EEG abnormalities):** Present in 75–90% of cases 9. **MRI findings:** Cerebral atrophy and white matter changes reflect progressive neurodegeneration **Clinical Pearl:** Rett syndrome almost exclusively affects **females** because the mutation is X-linked dominant and usually lethal in males (they die in utero or early infancy). Affected females survive because of random X-inactivation (lyonization), which creates a mosaic pattern of normal and mutant cells. ### Differential Diagnosis | Disorder | Key Distinguishing Feature | |----------|---------------------------| | **Rett syndrome** | Loss of purposeful hand skills + stereotyped hand movements + normal development until 6–18 months | | **Childhood disintegrative disorder (CDD)** | Normal development until age 3–4 years, then regression; **NO stereotyped hand movements**; autism-like features | | **Fragile X syndrome** | X-linked but **no regression**; developmental delay from infancy; macrocephaly, long face, large ears | | **Krabbe disease** | Lysosomal storage disorder; onset typically <6 months; rapidly progressive; death by age 2–3 | **Warning:** Do not confuse Rett syndrome with childhood disintegrative disorder (CDD). Both involve regression, but CDD lacks the **pathognomonic hand stereotypies** and the specific pattern of hand skill loss seen in Rett syndrome. ### Diagnostic Confirmation - **Genetic testing:** MECP2 gene mutation (gold standard) - **EEG:** Generalized spike-and-wave discharges, background slowing - **MRI:** Cerebral atrophy, white matter changes, corpus callosum atrophy - **Clinical diagnosis:** Based on diagnostic criteria (normal development, regression, hand stereotypies, seizures, ataxia/spasticity) ### Management 1. **Seizure control:** Antiepileptic drugs (valproate, levetiracetam) 2. **Supportive care:** Physical therapy, occupational therapy, speech therapy 3. **Behavioral management:** Address self-injurious behavior 4. **Genetic counseling:** Autosomal dominant X-linked inheritance; recurrence risk low (unless mother is a carrier) [cite:Kaplan & Sadock Comprehensive Textbook of Psychiatry 11e Ch 44; DSM-5 Neurodevelopmental Disorders]