A 3-year-old boy is brought to the developmental pediatrics clinic by his parents with concerns about delayed speech and social withdrawal. The child was developing normally until 18 months of age, when his parents noticed he stopped responding to his name, lost interest in playing with other children, and began repeating words without understanding their meaning. On examination, he makes poor eye contact, shows hand flapping when excited, and lines up toys in a row rather than engaging in pretend play. He has no significant medical history and normal hearing on audiometry. What is the most likely diagnosis?

Explanation

## Clinical Presentation Analysis **Key Point:** This case demonstrates Autism Spectrum Disorder (ASD) with a regressive course — normal development followed by loss of skills (regression) between 12–36 months of age. ### Core Features Present | Feature | Finding | ASD Criterion | |---------|---------|---------------| | Social communication | Loss of response to name, withdrawal from peers | Persistent deficit | | Restricted interests | Lining toys in rows (stereotyped play) | Restricted, repetitive behavior | | Repetitive behaviors | Hand flapping, echolalia (word repetition) | Stereotyped motor movements | | Onset | Normal until 18 months, then regression | Regressive ASD subtype | | Language | Loss of meaningful speech | Regression in communication | **High-Yield:** Regressive autism (loss of skills after 12–36 months) accounts for ~20–30% of ASD cases and is still classified as ASD under DSM-5, not as a separate disorder. ### Why This Is ASD and Not Alternatives 1. **Regression pattern** — The child had normal development, then lost social and communicative skills. 2. **Triad of deficits** — Social withdrawal + language regression + stereotyped behaviors (hand flapping, lining toys). 3. **Age of onset** — Regression in the 12–36 month window is characteristic of regressive ASD. 4. **Preserved hearing** — Rules out primary language disorder; the deficit is social-communicative. **Clinical Pearl:** Regressive autism was previously thought to be related to vaccines (now thoroughly disproven), but the regression is a genuine neurodevelopmental phenomenon. Parents often report a period of normal development followed by a plateau or loss of skills. **Mnemonic: RETT** — Remember that Rett Syndrome (X-linked) also shows regression, but it occurs in girls, includes characteristic hand stereotypies (hand wringing), and has a specific genetic cause (MECP2 mutation). This boy's presentation fits ASD, not Rett. ## DSM-5 Criteria for ASD **Key Point:** ASD is diagnosed on the basis of persistent deficits in social communication AND restricted, repetitive patterns of behavior, interests, or activities — regardless of whether onset was regressive or early. - Deficits in social-emotional reciprocity, nonverbal communication, and relationship development. - Restricted, repetitive behaviors (stereotyped movements, insistence on sameness, restricted interests, sensory sensitivities). - Symptoms present in early childhood (but may not fully manifest until social demands exceed capacity). - Symptoms cause clinically significant impairment. **High-Yield:** Regression does NOT change the diagnosis — it is still ASD. The specifier "with regression" may be noted in clinical documentation, but the diagnosis remains ASD.