A 2.5 year old boy is brought by the parents because of the concern that he is not developing appropriately. Child often is unable to engage with others using eye contact and does not play with other children. He has continuously bangs his chin against the wall and remains confined to himself most of the time. What is the most likely diagnosis?

**Core Concept**
The child's symptoms suggest a developmental disorder characterized by impaired social interaction, communication, and repetitive behaviors, which are hallmarks of Autism Spectrum Disorder (ASD).

**Why the Correct Answer is Right**
The child's inability to engage with others using eye contact, lack of play with other children, and repetitive behaviors such as banging his chin against the wall are indicative of ASD. These symptoms are often accompanied by delays in language development and cognitive impairment. The pathophysiology of ASD is complex and not fully understood, but it is believed to involve genetic and environmental factors that affect brain development.

**Why Each Wrong Option is Incorrect**
**Option A:** Rett Syndrome is a genetic disorder that affects girls almost exclusively, characterized by intellectual disability, loss of speech, and repetitive hand movements. This child's symptoms do not align with Rett Syndrome.
**Option B:** Attention Deficit Hyperactivity Disorder (ADHD) is a neurodevelopmental disorder characterized by symptoms of inattention, hyperactivity, and impulsivity. While children with ADHD may exhibit social difficulties, they typically do not have the same level of repetitive behaviors seen in ASD.
**Option C:** Sensory Processing Disorder (SPD) is a condition that affects the way the brain processes sensory information. While some children with SPD may exhibit repetitive behaviors, it is not typically associated with the same level of social impairment as ASD.
**Option D:** Fragile X Syndrome is a genetic disorder that causes intellectual disability, behavioral and learning challenges, and various physical characteristics. While it can cause developmental delays, it is not typically associated with the same level of social impairment as ASD.

**Clinical Pearl / High-Yield Fact**
Autism Spectrum Disorder is characterized by a spectrum of symptoms, and there is no single diagnostic test. A comprehensive diagnostic evaluation, including a detailed medical history, physical examination, and assessment of developmental and behavioral symptoms, is essential for an accurate diagnosis.

**Correct Answer:** C.

✓ Correct Answer: D. Autism