What is the primary condition occurring in an 18-month-old male with symptoms of hypotonia and self-harm?

The primary condition presented in the scenario is Lesch-Nyhan syndrome. This X-linked recessive disorder is characterized by a deficiency of the enzyme hypoxanthine-guanine phosphoribosyltransferase (HPRT), leading to an accumulation of uric acid in the body. While the typical age of onset for observable symptoms is often later than 18 months, early presentations can include developmental delays, hypotonia, and neurological features.

Self-harm behaviors, which may include biting of the lips or fingers, are notably associated with Lesch-Nyhan syndrome. These behaviors stem from a combination of the underlying neurological dysfunction and behavior regulation issues seen in affected individuals.

Understanding the neurodevelopmental context of such behaviors differentiates Lesch-Nyhan syndrome from conditions like Fragile X syndrome or cerebral palsy, which may involve hypotonia and developmental delays without the specific feature of self-harm. In the case of Amyoplasia, typically associated with arthrogryposis, the symptoms primarily focus on limb mobility issues rather than behavioral manifestations like self-harm.