Pallister–Killian syndrome (PKS) is a rare genetic developmental disorder characterized, by intellectual disability, seizures, streaks of hypo- or hyperpigmentation and characteristic dysmorphic features. PKS is characterized by the presence of cytogenetic abnormality in form of a supernumerary isochromosome 12p, in a tissue limited mosaicism. The isochromosome 12p is usually not detected in karyotype done from peripheral blood. Presence of patchy pigmentary skin lesions suggest the possibility of mosaicism and karyotype from skin is done which clinches the diagnosis. We describe an infant with severe hypotonia in whom trisomy 12p was detected by chromosomal microarray performed on peripheral blood. The karyotype from blood was normal and combining this information with three copies of 12p in microarray suggests the possibility of tetrasomy12p in mosaic form. The infant did not have any skin patchy pigmentary changes and malformations and hence, the diagnosis of PKS was not clinically suspected. Cytogenetic microarray is the first test for evaluation of cases with developmental delay and intellectual disability, PKS diagnosis may come as a surprise in unsuspected cases without characteristic skin pigmentary abnormality and malformations.

中文翻译：

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细胞遗传学微阵列诊断出患有 Pallister-Killian 综合征的低渗婴儿，无色素性皮肤改变和畸形

Pallister-Killian 综合征 (PKS) 是一种罕见的遗传发育障碍，其特征是智力障碍、癫痫发作、色素减退或色素沉着过度和特征性畸形特征。PKS 的特征是在组织受限的嵌合体中以多出的 12p 等染色体的形式存在细胞遗传学异常。外周血核型通常检测不到 12p 等染色体。斑片状色素性皮肤病变的存在表明可能存在嵌合体和来自皮肤的核型，从而确定了诊断。我们描述了一名患有严重肌张力减退症的婴儿，通过对外周血进行的染色体微阵列检测发现了 12p 三体。血液的核型是正常的，将此信息与微阵列中 12p 的三个拷贝相结合，表明镶嵌形式的四体 12p 的可能性。该婴儿没有任何皮肤斑片状色素改变和畸形，因此临床上不怀疑 PKS 的诊断。细胞遗传学微阵列是评估发育迟缓和智力障碍病例的第一个测试，在没有特征性皮肤色素异常和畸形的意外病例中，PKS 诊断可能会令人惊讶。