The Xq26 locus has importance in human growth with multiple genes and regions playing important roles, which potentially leads to macrosomia or microsomia if disrupted. One region of Xq26.2 comprises the genes GPC3 and GPC4; deletion or duplication of this region has been recently been shown to result in overgrowth, specifically Simpson–Golabi–Behmel syndrome. We describe a male patient with two maternally inherited Xq26 microduplications; the first was 0.8 Mb at Xq26.2 affecting only GPC3 and GPC4, and the second, a distal 0.6 Mb duplication at Xq26.3 affecting seven genes. Rather than having Simpson–Golabi–Behmel syndrome, our patient had microcephaly and undergrowth, with development that was within normal limits at 25 months of age. This finding suggests that the molecular pathway leading to overgrowth secondary to GPC3/GPC4 haploinsufficiency can be overpowered by a disruption to the distal Xq26.3 region. Of the genes in that region, we propose that SLC9A6 is the most likely to play an important role as mutations in this gene lead to Christianson syndrome, in which patients may have microcephaly and weight loss.

中文翻译：

---

Xq26 重复通过包括 GPC3/GPC4 在内的竞争途径导致生长不足或过度生长

Xq26 基因座在人类生长中具有重要意义，多个基因和区域发挥重要作用，如果被破坏，可能会导致巨大儿或小儿。Xq26.2 的一个区域包含基因 GPC3 和 GPC4；该区域的缺失或重复最近已被证明会导致过度生长，特别是 Simpson-Golabi-Behmel 综合征。我们描述了一名男性患者，有两个母系遗传的 Xq26 微重复；第一个是 Xq26.2 处的 0.8 Mb 仅影响 GPC3 和 GPC4，第二个是 Xq26.3 处的远端 0.6 Mb 重复，影响七个基因。我们的患者没有 Simpson-Golabi-Behmel 综合征，而是小头畸形和发育不良，在 25 个月大时发育在正常范围内。这一发现表明，导致继发于 GPC3/GPC4 单倍体不足的过度生长的分子途径可以被远端 Xq26.3 区域的破坏所压制。在该区域的基因中，我们认为 SLC9A6 最有可能发挥重要作用，因为该基因的突变导致克里斯蒂安森综合征，患者可能患有小头畸形和体重减轻。