Prevention of intellectual disability through screening for congenital hypothyroidism: how much and at what level?
OBJECTIVE
Congenital hypothyroidism (CHT) is a common cause of preventable mental retardation, and the quantification of intellectual disability due to CHT is needed to assess the public health benefit of newborn screening.


METHODS
Review of published studies conducted among children born prior to the introduction of newborn screening for CHT and reporting cognitive test scores.


METHODS
Population-based studies.


METHODS
Children with clinically diagnosed CHT.


METHODS
Thyroid hormone substitution.


METHODS
Intelligence quotient (IQ) (mean and distribution).


RESULTS
The prevalence of recognised CHT rose from one in 6500 prior to screening to approximately one in 3000 with screening. In four population-based studies in high-income countries, among children with clinically diagnosed CHT 8-28% were classified as having intellectual disability (defined as an IQ <70) and the mean IQ was 85 (a leftward shift of 1 SD). Among children with subclinical CHT, the risk of overt intellectual disability was lower (zero in one study), but decreased intellectual potential and increased behavioural abnormalities were documented.


CONCLUSIONS
Although the prevalence of overt disability among children with CHT in the absence of screening may be less than previously estimated, the preventable burden of intellectual disability due to CHT is substantial and justifies newborn screening. However, changes in existing newborn screening protocols to capture more cases are unlikely to prevent overt cases of disability and should therefore be justified instead by the documentation of other benefits of early detection.
Centers for Disease Control and Prevention, 1600 Clifton Road, Atlanta, GA 30333, USA. sgrosse@cdc.gov
Scott D
SD
Grosse
Guy
G
Van Vliet
D003409:Congenital Hypothyroidism / Q000175:diagnosis* / Q000188:drug therapy / Q000453:epidemiology / Q000523:psychology; D020249:Hormone Replacement Therapy / Q000379:methods; D006801:Humans; D007231:Infant, Newborn; D008607:Intellectual Disability / Q000453:epidemiology / Q000209:etiology / Q000517:prevention & control*; D007360:Intelligence; D015997:Neonatal Screening / Q000379:methods*; D013963:Thyroid Hormones / Q000627:therapeutic use
D013963:Thyroid Hormones