Phelan-McDermid syndrome (PMS) is a 22q13.3 deletion syndrome. Most PMS patients show global developmental delay and some of them suffer from developmental regression. The deleted region contains ARSA, which is responsible for metachromatic leukodystrophy (MLD). Here we report an extremely rare case of PMS characterized by unusual, rapidly progressive developmental regression due to additional pathogenic mutation in ARSA. Considering the 1 in 100 chance of an MLD carrier, co-occurrence of PMS and MLD in a patient is possible if either parent carries a heterozygous ARSA mutation. Therefore, MLD should be ruled out in PMS patients with severe neurological phenotype.

中文翻译：

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一例退化性 Phelan-McDermid 综合征患者异染性脑白质营养不良的诊断

Phelan-McDermid 综合征 (PMS) 是一种 22q13.3 缺失综合征。大多数 PMS 患者表现出整体发育迟缓，其中一些患有发育倒退。删除的区域包含 ARSA，它负责异染性脑白质营养不良 (MLD)。在这里，我们报告了一个极其罕见的 PMS 病例，其特征是由于 ARSA 中的额外致病突变导致的异常、快速进行性发育退化。考虑到 MLD 携带者的几率为 100 分之一，如果父母一方携带杂合 ARSA 突变，则患者可能同时发生 PMS 和 MLD。因此，对于具有严重神经表型的 PMS 患者，应排除 MLD。