Congenital hypothyroidism and IQ increase: a quarter century follow-up

Congenital hypothyroidism: From paracelsus to molecular diagnosis

Endemic cretinism was noted in alpine Europe as early as the 13th century. However, it was only in 1848 that a commission, sponsored by the King of Sardinia, first formally demonstrated its link to goiter. An important landmark was the publication of a report in 1871 describing several cases of nongoitrous hypothyroidism that were clearly distinguished from the endemic form of the disease, for which the author suggested the designation of "sporadic cretinism." Classification of the hypothyroid status was for a long time solely based on clinical observation. In the second half of the 20th century, the use of radionuclides (iodine radioisotope and technetium pertechnetate) allowed a more precise diagnosis and taxonomy into thyroid dysgenesis and dyshormonogenesis. This brief review summarizes the progress that has been achieved during the last 40 years in diagnosing the multiple variants of congenital hypothyroidism (CH). It becomes evident that while accurate diagnosis for CH is readily available, its exact etiology requires a precise molecular investigation as different genes are implicated in the differentiation, migration and growth of the thyroid gland.

Neuropsychologic development in early treated congenital hypothyroidism: analysis of literature data

The aim of this study was to determine the neuropsychologic development in patients with congenital (primary) hypothyroidism (CH) detected by screening and treated from early age. Seven studies were evaluated, including 675 CH patients and 570 controls. Criteria for inclusion of the studies were: 1) age of patients and controls > or = 5 y; 2) control group well defined in the original article. A meta-analysis of the data on the intellectual development was performed. All analyzed studies show a trend toward lower intelligence quotient (IQ) and--as far as investigated--poorer motor skills in CH patients compared with controls. Pooling of data showed a significant deficit of the mean IQ of 6.3 (95% confidence interval: 4.7-7.8). The most important independent risk factor for the eventual outcome appears to be the severity of CH (defined by initial thyroxine at the moment of diagnosis and by skeletal maturation); treatment variables do not seem to have an important effect the cognitive development. We conclude that CH, despite early detection and treatment, results in an IQ deficit; the severity of CH seems to be the most important individual risk factor. Our second conclusion is that, although biomedical risk factors are well investigated, the individual weight of these factors is yet largely unknown. This may be due to the variability of definitions and test tools, especially for the investigation of motor skills, that have been used.

Multicentre study of a new test for TSH-screening in blood spots

A multicentre study for the detection of congenital hypothyroidism by enzyme-immunoassay of thyrotropin in filter paper blood spots is described. The method is accurate, with good precision and adequate sensitivity. No interference due to common blood constituents has been observed. Moreover, the TSH determination can easily be performed by photometric measurement of enzyme activity. Large series of samples can be processed by automation using common laboratory analysers. Values show good agreement with those obtained by RIA methods. We present a method for screening for congenital hypothyroidism which can be performed in all clinical laboratories.

Personality traits and mental prognosis in patients with congenital hypothyroidism not treated from early life

Congenital hypothyroidism, if not treated in very early life, severely impairs the neuropsychological development of affected subjects. We have carried out a detailed analysis of cognitive functioning and personality traits in 18 congenital hypothyroid patients treated late and/or unproperly. Significant cognitive defects were observed, the most important being a defective learning ability and an impaired capacity to judge socially significant events and to project complex actions in a temporal perspective. A mental retardation (IQ less than 70) was observed in 8/18 (44.4%) of these patients, a moderate intellective deficit in 5/18 (27.8%) and an IQ greater than 85 in the remaining 5 patients (27.8%). These data indicate that the mental defect of congenital hypothyroid patients may be overestimated. The patients personality was characterized by dependence on the mother, worrying about their body, maladjustment and socialization problems. Since the intellective prognosis of these patients may significantly improve when the environmental conditions are optimized, social and psychological help must always be suggested.

A comparison between the neurological and intellectual abnormalities in children and adults with congenital hypothyroidism

Standardised intellectual, motor and behavioural tests have been undertaken in a group of 73 children and 43 adults with congenital hypothyroidism in a regional study in the north of England. These provide comprehensive data with which to compare the results of studies of children diagnosed by screening and indicate the degree of abnormalities persisting into adult life in those patients diagnosed before screening was introduced. The mean IQ scores of the hypothyroid children and adults were 1-2 standard deviations (SD) below the population means. Longitudinal IQ data indicate persistence of intellectual abnormalities, though there was an increase in IQ score in several patients. The mean motor scores were reduced by 1-2 SD in the children and 1-3 SD in the adults. Behavioural problems and personality difficulties mainly of a neurotic nature also persisted into adult life.

Outcome for congenital hypothyroidism

In a study designed to provide retrospective control data for a neonatal thyroid screening programme, the problems of 141 hypothyroid children were examined. The mean IQ (Weschler intelligence scale) was 79.5 for children with congenital hypothyroidism but was normal in 6 children diagnosed before age 6 weeks. Diagnostic delay was associated with a steady decline in mean IQ but there was an improvement in some late diagnosed cases. A strong association was found between IQ and parental social class. Twenty five percent of the children were mentally retarded and 29% were at special schools; 54% of children at normal schools and 43% at special schools showed deviant behaviour. Other problems included clumsiness (26.2%) and squints (26.2%), and these were more common in children with a lower IQ. Congenital hypothyroidism is associated with persistent morbidity in many aspects of cerebral function. The adverse effects of prenatal hypothyroidism are largely reversible if treated before age 6 weeks.

Congenital hypothyroidism: age at start of treatment versus outcome

We studied 27 patients with congenital hypothyroidism by neurological and psychometric methods. 7 healthy siblings served as a control group for the psychometric evaluation. In 7 patients treatment had been started before the age of 1 month and in 10 patients after the age of 3 months. Our findings suggest that the progressive loss of intelligence potential starts from birth but if treatment is begun before the age of 1 month, then intelligence remains within normal range. The neurological damage seems to originate partly before birth, but more serious injuries arise if treatment is delayed beyond the age of 3 months.

Growth of intelligence: failure and catch-up associated respectively with abuse and rescue in the syndrome of abuse dwarfism

IQ change in association with change of environment occurred in a sample of 34 patients with a diagnosis of abuse dwarfism. Low and persistent impairment of IQ was associated with abuse. By contrast, IQ elevation was associated with rescue. Multiple regression analysis revealed that duration of rescue was the primary variable associated with IQ elevation; age and IQ level at rescue were secondary. IQ elevation was gradual and progressive over the years, as rescue was maintained. In abuse, the mean IQ was 66 (range, 36-101), and after rescue it was 90 (range 48-133). The greatest magnitude of change, from IQ 36 to 120, was in a girl between the ages of 3 yr 8 months and 13 yr 11 months.

Neonatal screening for congenital hypothyroidism

Presently active screening programs for the detection of congenital hypothyroidism are highly effective in the diagnosis of intrinsic disease of the thyroid associated with both hypothyroxinemia and elevated serum TSH. For other disorders of thyroid function, which are numerically less important, the programs are hampered by a high rate of false positive results. The physician's response to notification of suspect status for a given infant must be guided by an understanding of the specific nature of the screening program in his area.

Neuropsychological study in treated thyroid dysgenesis

Neuropsychological assessment was carried out in 57 patients aged 3.0 to 17.5 years (mean 8.5) with thyroid dysgenesis under adequate long-term therapy. Starting age of hypothyroidism as estimated by bone age at diagnosis was prenatal in 32 cases, close to birth in 13 cases and postnatal of 1-12 months in 12 cases. Hypothyroidism of prenatal onset results in severe neuropsychological disorders and mental retardation if not treated early. Only some signs of "minimal brain dysfunction" which compensate with advancing age and normal IQ are found in these children if therapy is started before one month of age. Hypothyroidism starting at birth does not result in mental retardation but neuropsychological disorders are found. They are more frequent if treatment is started after 6 months of age. Children who become hypothyroid between 1 and 12 months of age are usually not mentally retarded and show minor neuropsychological disorders.