六、治疗和结果
T3是具备生物活性的甲状腺激素，由T4脱碘而来，由于脑组织优先选择应用T4来补充对T3的需求，因此治疗先天性甲减的最重要目标就是补充T4来修复甲减对脑发育的损伤[2]。
从理论上来讲，对遗传缺陷性甲减或者是后天获得性甲减的儿童的治疗原则是相似的，都是通过口服补充T4，每日剂量也应该随着快速增加的体重而不断增加，并通过定期复查TSH和FT4来调整剂量。由于在婴儿体内T4的半衰期要短于儿童和成人[1]，所以其日需求量要偏高。但尽管半衰期偏短，每日1次给药也足以维持稳定的FT4和TSH水平。对于甲状腺性先天性甲减的患者，经过T4充分治疗之后的血清FT4水平要比正常人或经过治疗的自身免疫性甲状腺病患者要偏高，血清FT3水平则无明显差异。FT4的这种差异可能与胎儿时期的甲减状态持续时间有关[45]。
在新生儿甲减筛查已普及的地区，目前普遍认同的观点是，甲状腺激素在产前的胎儿脑发育中并非必不可少，先天性甲减患者一般不会进展为神经发育迟缓，因此推荐出生后再开始补充甲状腺激素。有证据表明，在胎儿甲状腺发育成熟之前，母体的T4完全可以满足胎儿对甲状腺激素的需求。因此当患儿存在先天性甲减时，母体的T4可以延缓甲减症状的出现，减轻甲状腺肿，预防脑发育中严重和不可逆的损伤[3]。
未经治疗的先天性甲减会有脑发育损伤的风险，影响成年后的认知和运动功能。然而未经治疗的轻度先天性甲减的风险仍不明确，仅有有限证据表明早期的补充T4会改善认知功能。谨慎起见，建议对所有发现甲减的婴儿，无论是严重还是轻微的都要立即给予治疗[46]。等到3～4岁时再停药重新评估先天性甲减的诊断，如可确诊再进一步明确病因。
对于甲状腺性先天性甲减患者，TSH可以作为是否建立正常甲状腺功能的主要评价指标，但对于中枢性先天性甲减患者则需要应用FT4来评估治疗效果。研究表明中枢性先天性甲减患者的血清FT4应保持在年龄参考范围的上限[45，47]。
在大多数累及甲状腺激素合成的遗传缺陷中，在TSH仅轻微增高时，甲状腺也会出现增生和结节。而如果T4补充较早的话，并且血清TSH水平维持正常时，甲状腺增生则不会出现。
遗传缺陷的类型也决定了治疗的选择，比如对于碘化物循环障碍的患儿，给予大量的碘可以维持甲功正常，但事实上给予T4更为方便。对于甲状腺激素抵抗的患儿，治疗选择取决于其严重程度以及外周组织和垂体对甲状腺激素的反应性，对抵抗明显的还是应给予T4的治疗。对于甲状腺激素跨膜转运障碍的患儿，T4或T3的治疗获益还不明确。
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