Mayatepek and Flock (1998) described the inability to synthesize LTC4, thought to be due to a primary deficiency of LTC4 synthase (LTC4S; 246530), in an infant with a fatal developmental syndrome. The infant presented with muscular hypotonia, psychomotor ... Mayatepek and Flock (1998) described the inability to synthesize LTC4, thought to be due to a primary deficiency of LTC4 synthase (LTC4S; 246530), in an infant with a fatal developmental syndrome. The infant presented with muscular hypotonia, psychomotor retardation, failure to thrive, and microcephaly. The course of the disease was rapidly progressive and the infant died at the age of 6 months. The patient was the daughter of consanguineous Turkish parents. Mayatepek et al. (2000) reported another patient with LTC4S deficiency, a girl born at 33 weeks' gestation to consanguineous Italian parents. She had generalized muscular hypotonia with lack of facial expression from the first day of life. After the first week of life, she developed symmetric extension in the lower extremities, including stretching of the trunk musculature. During the course of the disease, severe muscular hypotonia and failure to thrive with tendency to microcephaly became rapidly progressive. There were no pyramidal tract signs, and deep tendon reflexes were not present. She had no psychomotor development and there was no visual contact at any time. It was impossible to extubate the patient, and the infant died at 6 months of age.