Smith-Kingsmore syndrome with nystagmus as the initial symptom

Smith-Kingsmore syndrome (SKS) is a rare autosomal dominant disorder caused by de novo mutations of gene MTOR in most cases and germline mosaicism in a few cases. The first case of SKS was reported in 2013. The incidence of SKS remains unknown. The clinical manifestations of SKS are diverse, and common features are macrocephaly, intellectual disability, and seizures. Some patients with SKS have special facial features.

The case was a 5-month-old baby girl, who was admitted to the hospital for nystagmus, delayed development for 2 months, and intermittent convulsions for 2 days. The patient had a head circumference of 42 cm (+ 2SD), and showed facial deformity, low limb muscle tension, large areas of pigmentation, as well as mosaic patchy and strip-like pigment loss in her trunk and limbs. Meanwhile, her development was lagging behind peers. Physical examination did not reveal other abnormalities. She was diagnosed with SKS based on whole-exome sequencing combined with clinical symptoms and signs. She successively received treatment with adrenocorticotropic hormone, methylprednisolone sodium succinate, topiramate, levetiracetam, and zonisamide to reduce the number of convulsions in a short time, but drug resistance appeared thereafter. After combined treatment with multiple antiseizure medications, the patient still had seizures, but the amplitude of limb movement during the seizures was reduced compared to that before treatment.

This case expanded the phenotypic spectrum of SKS for diagnosis. We also review the related literature to promote the awareness, diagnosis, clinical management, and follow-up of SKS patients with MTOR mutations.