Normally, during fetal development there's a region of the brain called the olfactory placode.

正常情况下，在胎儿发育期间，大脑中有一个区域被称为嗅觉基板。

In Kallmann syndrome, there's a defect in the migration of the neurons coming out of the olfactory placode.

在Kallmann综合征中，神经元迁移出嗅觉基板存在缺陷。

These neurons migrate down from the olfactory placode and get embedded in the cribriform plate, which is a bone plate that separates the nasal cavity from the brain, forming the olfactory bulb.

这些神经元从嗅觉基板迁移下来，并嵌入筛板中，即将鼻腔与大脑隔开的骨板，从而形成嗅球。