Definition:

Spondylometaphyseal dysplasia with cone-rod dystrophy (SMD-CRD) is a rare presumed autosomal-recessive disorder with postnatal growth deficiency leading to profound short stature; rhizomelia with bowing of the lower extremities; platyspondyly with anterior vertebral protrusions; progressive metaphyseal irregularity and cupping with shortened tubular bones; and early-onset, progressive visual impairment associated with a pigmentary maculopathy and electroretinographic evidence of cone-rod dysfunction. Spondylometaphyseal dysplasias (SMDs) are a heterogeneous group of disorders radiologically characterized by platyspondyly and metaphyseal dysplasia. Extra-skeletal abnormalities associated with SMDs are uncommon. In 2004, a unique form of SMD associated with cone-rod dystrophy (CRD) was described and defined as SMD-CRD. Loss-of-function mutations in PCYT1A have been reported as the cause of SMD-CRD.