Okay, let's tackle this question. The baby is one month old with vomiting, irritability, jaundice, hepatomegaly, and abnormal LFTs after starting cereals and fruit juices. The key here is the age and the dietary change.

First, I need to think about metabolic disorders that present in infants. Galactosemia comes to mind because it's a classic condition where babies can't process galactose, leading to liver issues, jaundice, and other symptoms. The introduction of lactose-containing foods like cereals (if they have milk) or fruit juices (maybe apple juice has galactose?) could trigger symptoms.

The enzyme deficiency in galactosemia is galactose-1-phosphate uridyltransferase. Without this, galactose builds up, causing toxicity. The symptoms align: jaundice, liver problems, and the timing after introducing new foods.

Now, other options: maybe fructose intolerance or tyrosinemia. Fructose intolerance would present after fructose intake, but the question mentions cereals and fruit juices. If the juice is apple or grape, maybe fructose, but galactosemia is more classic with early presentation. Tyrosinemia type I can cause liver issues but usually has more specific features like renal tubular dysfunction.

The USG showing hepatomegaly and abnormal LFTs point to a metabolic liver issue. The key is the age and the dietary trigger. Galactosemia is typically diagnosed in the first few weeks of life, and introducing lactose (from milk in cereals) would exacerbate it.

So the correct answer is galactose-1-phosphate uridyltransferase deficiency. The other options don't fit as well. The clinical pearl here is to remember that galactosemia presents early, and dietary history is crucial.

**Core Concept**
This question tests the recognition of **galactosemia**, a metabolic disorder caused by deficiency of **galactose-1-phosphate uridyltransferase**, leading to galactose toxicity. It typically presents in infants after lactose intake (e.g., formula or dairy), causing jaundice, liver dysfunction, and vomiting.

**Why the Correct Answer is Right**
Galactose-1-phosphate uridyltransferase deficiency impairs galactose metabolism, causing accumulation of galactose-1-phosphate and toxic metabolites. These damage the liver, kidneys, and brain. In this case, the infant's symptoms (jaundice, hepatomegaly, irritability) post-dietary introduction of lactose-containing foods (cereals, juices) align with classic galactosemia. Early diagnosis prevents cataracts, sepsis, and intellectual disability.

**Why Each Wrong Option is Incorrect**
**Option A:** *Fructokinase deficiency* (essential fructosuria) is asymptomatic and does not cause liver damage.
**Option B:** *Glucose-6-phosphatase deficiency* (von Gierke disease) causes hypoglycemia, lactic acidosis, and glycogen accumulation but presents in infancy, not typically triggered by dietary changes.
**Option C:** *Pyruvate dehydrogenase deficiency* causes lactic acidosis and neurological symptoms, unrelated to dietary galactose/fructose.

**Clinical

✓ Correct Answer: B. Aldolase-B