NKX2-1-related disorders range from benign hereditary chorea (BHC) to choreoathetosis, congenital hypothyroidism, and neonatal respiratory distress (also known as brain-lung-thyroid syndrome). Childhood-onset chorea, the hallmark of NKX2-1-related disorders, may or may not be associated with respiratory distress syndrome or congenital hypothyroidism. Chorea generally begins in early infancy or about age one year (most commonly) or in late childhood or adolescence, and progresses into the second decade after which it remains static or (rarely) remits. Pulmonary disease, the second most common manifestation, can include respiratory distress syndrome in neonates, interstitial lung disease in young children, and pulmonary fibrosis in older persons. The risk for pulmonary carcinoma is increased in young adults with an NKX2-1-related disorder. Thyroid dysfunction, the result of dysembryogenesis, can present as congenital hypothyroidism or compensated hypothyroidism. The risk for thyroid cancer is unknown and may not be increased. In one review, 50% of affected individuals had the full brain-lung-thyroid syndrome, 30% had involvement of brain and thyroid only, and 13% had isolated chorea only.

For a general phenotypic description and a discussion of genetic heterogeneity of pulmonary surfactant metabolism dysfunction, see SMDP1 (265120).

Pulmonary surfactant metabolism dysfunction-2 (SMDP2) is a rare autosomal dominant disease associated with progressive respiratory insufficiency and lung disease with a variable clinical course. The pathophysiology of the disorder is postulated to involve intracellular accumulation of a structurally defective SPC protein (Thomas et al., 2002). For a general phenotypic description and a discussion of genetic heterogeneity of pulmonary surfactant metabolism dysfunction, see SMDP1 (265120).