A 7-month-old child presented with neuro-developmental delay, loss of motor skills, increased stale reaction to noise, feeding difficulties & failure to thrive. On examination, macrocephaly was noted along with myoclonus and spasticity. There was no evidence of any corneal clouding or angiokeratomatas. On investigating fuher, CT scan reveals no hepatosplenomegaly and no cardiac involvement. Fundoscopy reveals – Which enzyme deficiency is responsible for above symptoms?

**Core Concept:** Enzyme deficiencies can lead to various clinical presentations depending on the specific enzyme involved. Neurodevelopmental delay, motor skills loss, and abnormal reflexes can be seen in certain enzymatic disorders. Macrocephaly and myoclonus are neurological symptoms, while feeding difficulties, failure to thrive, and spasticity are related to impaired growth and development.

**Why the Correct Answer is Right:** The clinical presentation described is consistent with a deficiency in the enzyme Gamma-aminobutyric acid (GABA) transaminase, also known as glutamate decarboxylase (GAD). This enzyme plays a crucial role in the synthesis of GABA, a neurotransmitter involved in regulating neuronal excitability and synaptic transmission. A deficiency in GAD leads to a decrease in GABA levels, which results in increased neuronal excitability, causing various symptoms.

**Why Each Wrong Option is Incorrect:**

A. GABA transaminase deficiency (Option D) is a rare condition, not commonly associated with the specific symptoms described.
B. Cystathionine beta-synthase deficiency (Option C) is linked to homocysteine elevation, not the neurological symptoms mentioned.
C. GABA transaminase deficiency (Option C) is not the correct answer as mentioned above.

**Clinical Pearl:** A thorough understanding of enzyme deficiencies and their associated symptoms is essential for accurate diagnosis and treatment. Enzyme deficiencies, including GABA transaminase deficiency, should be considered in infants presenting with neurological symptoms, growth impairment, and abnormal reflexes. Early diagnosis and treatment can significantly improve the child's prognosis and overall outcome.

✓ Correct Answer: A. Hexosaminidase A