What is the primary effect of leptin receptor deficiency in neonates?

Leptin is a hormone produced by adipocytes (fat cells) that plays a crucial role in regulating energy balance by inhibiting hunger, which in turn helps to regulate body weight. The primary effect of leptin receptor deficiency in neonates is severe obesity. When leptin receptors are deficient or malfunctioning, the body is unable to respond to leptin's signals effectively. This leads to an unregulated appetite and increased food intake because the sensation of satiety that normally helps control eating behavior is significantly impaired. As a result, neonates with this deficiency tend to overeat, leading to excessive weight gain and ultimately severe obesity, often beginning in infancy.

The other options do not accurately describe the primary consequence of leptin receptor deficiency. For instance, increased metabolism and reduced appetite would typically be outcomes of an effective leptin signaling pathway, not a deficiency. Additionally, heightened immune response is not a well-documented effect of leptin receptor deficiency.