[Neonatal hypothyroidism. pathophysiogenic, molecular and clinical aspects].

This review provides an updated summary on both the clinical and diagnostic aspects of neonatal hypothyroidism (NeH); as well as on the molecular and pathophysiologic processes known to be involved in the installment of this important hormonal deficiency. Current information regarding its etiology and pathogenesis has allowed classigying NeH in three major groups: endemic, transient, and sporadic hypothyroidism. The later corresponds to congenital hypothyroidism and encompasses a broad spectrum of hereditary disorders causing hypothyroidism in newborns and young children. These congenital disorders include hypothalamic-pituitary or thyroid dysgenesis and/or dyshormonogenesis, as well as hyporesponsiveness or resistance to either TRH, TSH or to thyroid hormones. The introduction of national screening programs for NeH have overcome the difficulties in the early diagnosis thus helping to prevent its serious and irreversible consequences on intellectual and physical development. Concomitantly, an increase in the need for complementary etiologic and molecular diagnosis has risen. The current capability to perform a fine and precise diagnose is crucial both for treatment of the affected infant and for genetic counseling of the family. Although incomplete, available epidemiological information in Mexico indicates that NeH prevalence can be as high as twice that in other developed world countries. On these bases, national public health policies and epidemiological surveyance must be strengthen not only to identify. diagnose and timely treat, but to prevent and eradicate endemic NeH.