We describe the patient of a 23-year-old female with Laron syndrome who was the first case of GH-receptor gene mutation detected in Japan. Her height and weight were 125.0 cm (-6.6 SD) and 56.0kg. Her father and one of her three brothers were 158 cm (-2.2 SD) and 160 cm (-1.9 SD) in height, respectively, but her mother and remaining two brothers were of normal height. Serum growth hormone (GH) concentration was high in basal levels (9.6-23.6ng/ml) and reached extremely high levels responding to the provocative tests of insulin hypoglycemia and arginine infusion (60.8 and 104.8ng/ml, respectively). Serum IGF-I concentration was low (42ng/ml), serum GH-binding protein level was undetectable at less than 1.16ng/ml, and serum IGF-binding protein-3 level was 0.51μg/ml (normal: 2.59-4.26).
Each exon and flanking part of intron of the GH-receptor gene from the genomic DNA by PCR was sequenced. A G to A mutation was identified at the first position of intron 4. This mutation was homozygous and could possibly cause an abnormal splice site resulting in a production of abnormal GH-receptor protein.