An 8-year-old male patient with Spondylo-Epiphyseal Tarda with Progressive Arthropathy (SEDT-PA) or Progressive Pseudo-rheumatoid Arthropathy of Childhood is reported. Abnormal gait, fatigability, and joint symptoms began at 3 years. Radiological changes were: generalized osteoporosis, platyspondyly, and enlarged epiphyses. The patient's mother showed reduced muscular massa, joint swelling, moderate osteoporosis, and normal vertebrae. SEDT-PA has an autosomal recessive mode of inheritance. In this case, as the propositus' mother showed minimal signs of the disease, either an X-linked trait or an autosomal dominant mutation with variable expressivity could also be assumed.