Abstract: AbstractObjective：To report one case of male focal dermal hypoplasia (FDH) caused by mosaic mutation of PORCN for clinical diagnosis reference. Methods：The clinical manifestations, laboratory measurements and gene sequencing results were summarized.PORCN mutations from Pubmed, Wanfang Database and China National Knowledge Infrastructure up to September 30th, 2017 were searched, the related features along with the clinical and gene mutation spectrums of the survived FDH male cases were summarized.Results：A 12 years and 2 months old boy with height 142 cm (-1.4 SD) and weight 36.1 kg was referred to our clinic due to short stature. The serum IGF1 level was 323.8 ng·mL-1 and IGFBP3 level was 4.9 μg·mL-1.No abnormalities were found in his pituitary and bilateral testes and adrenal gland. However, typical features were found as short left fourth toe, skin hypopigmentation at his left leg and abdomen along Blaschko line, and fat herniation in buttocks and penis. Bipedal X-ray showed that the 1st, 4th, 5th metatarsal of left foot, left great toe and the 4th phalanges were small, the phalanges of left great toe were short with small end. Six steroid sex hormones were within normal range. WISC-R intellectual test demonstrated that language and total scores are marginally low. Mosaic c.178G> A mutation of PORCN gene was detected by whole exon sequencing and confirmed by Sanger sequencing, then the diagnosis of FDH was made. A total of 205 reported patients confirmed having PORCN mutations were reported in 36 literatures and only 22 were males(3 cases died soon after birth). The most frequently reported symptoms were skin hypoplasia (72.7%),skeletonabnormalities (66.8%) and craniofacial anomalies (58.5%). The survived male patients were all mosaic or postzygotic mosaic mutations except one 46, XXY Klinefelter syndrome whose clinical manifestations showed great heterogeneity but all with skin hypoplasia.Conclusion：The FDH patient we reported not only presented with limb and skin abnormalities, but also with mental retardation. Male patients could be misdiagnosed by Sanger sequencing because of the failure of detection of mosaic mutation and great heterogeneity of clinical manifestations.WES test could significantly improve the positive rate of diagnosis for those suspected male patients.