[Achondrogenesis type II-hypochondrogenesis: radiological features.Case report].

We present a case of lethal dysplasia in the neonatal period. The abnormality was suspected after ultrasonography of a pregnant woman presenting weak fetal movements revealed shortening of the extremities, voluminous cranium and polyhydramnios. Clinical and radiological findings showed platyspondylic dwarfism with short extremities, narrow thorax and hydropic appearance. The infant died on the third day of life from progressive respiratory distress. In the absence of histological, chondro-osseus and molecular studies, detailed clinical and radiological studies, as well as the lethal evolution during the neonatal period, guided the diagnosis of hypochondrogenesis. This entity, together with achondrogenesis II (and other dysplasias), forms part of the same spectrum of collagen type II abnormalities produced by a defect in the gene (COL2A1) that codifies collagen II, located in chromosome 12 I(12q13.1-13.2). When a heterozygote is produced, transmission is dominant autosomal. The phenotype shows wide variation and severity depends on the mechanism and location of the mutation. The definitive diagnosis is given by cytomolecular studies, while individualization of the different entities is based on histological data from the cartilage; clinical findings and skeletal radiology serve as a guide.