Vitamin D plays an important role in calcium homeostasis and bone mineralization. Inefficient inactivation of vitamin D leads to a condition called idiopathic infantile hypercalcemia (IIH). In the last decade mutations in CYP24A1, the gene responsible for vitamin D inactivation, were described as the main molecular cause of IIH.

In this study, we present a family with two daughters diagnosed with IIH due to two different mutations in CYP24A1 gene. Based on next-generation sequencing (NGS), the elder daughter was diagnosed as carrying the mutations CYP24A1: c.1186C > T; (p.Arg396Trp) and c.428_430del; (p.Glu143del). Within this context, we were able to presymptomatically diagnose her newborn sister using Sanger sequencing technique.

Screening for CYP24A1 mutations in families with IIH history helps preventing disease manifestations in newborn siblings. Thus, NGS combined with Sanger sequencing validation opens up the perspective of preventive medicine with great impact on IIH management, where stopping vitamin D administration is enough to prevent disease manifestation, in most cases.

维生素D在钙稳态和骨骼矿化中起重要作用。维生素D的无效灭活会导致一种称为特发性婴儿高钙血症（IIH）的疾病。在最近十年中，CYP24A1突变（引起维生素D失活的基因）被描述为IIH的主要原因。

在这项研究中，我们介绍了一个有两个女儿的家庭，这些女儿由于CYP24A1基因的两个不同突变而被诊断出患有IIH 。根据下一代测序（NGS），大女儿被诊断出携带CYP24A1突变：c.1186C> T；（p.Arg396Trp）和c.428_430del; （第Glu143del页）。在这种情况下，我们能够使用Sanger测序技术对症状进行诊断。

在具有IIH历史的家庭中筛查CYP24A1突变有助于预防新生儿兄弟姐妹的疾病表现。因此，NGS与Sanger测序验证相结合，开辟了预防医学的前景，对IIH管理产生了重大影响，在大多数情况下，停止服用维生素D就足以预防疾病表现。