TPST2 and Primary hypothyroidism: We also reported that Tpst2-/- mice have mild-moderate primary hypothyroidism, whereas Tpst1-/- mice are euthyroid [18] consistent with the observations by Sasaki et al. that a spontaneous mutation in the Tpst2 gene is responsible for an autosomal recessive form of primary hypothyroidism in the grt/grt mouse [19].