Sema3d and PHPT (IMAGE) Duke-NUS Medical School Caption Four small parathyroid glands located in the neck behind the larger thyroid are responsible for managing healthy blood calcium levels. Primary hyperparathyroidism is marked by excessive parathyroid hormone secretion due to parathyroid hyperplasia, which leads to increased serum calcium levels and causes kidney stones, neuropsychiatric disorders and bone abnormalities. Researchers in Singapore and India, led by Duke-NUS Medical School, found that a signalling protein required for parathyroid gland development, called semaphorin3d (Sema3d), protects the glands from excessive growth by inhibiting cell proliferation. Credit Duke-NUS Medical School Usage Restrictions Image may only be used with the above prescribed caption or similar and the credit. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.