Prevalence of abnormal thyroid function tests in a Down's syndrome population

Thyroid function in Down syndrome

Down syndrome is the most commonly encountered human chromosomal disorder. Down syndrome is associated with thyroid dysfunction including: hypothyroidism, both congenital and acquired, and hyperthyroidism. A genetic predisposition and a propensity to acquire autoimmune disorders seem to be possible factors, though their causal relation remains unclear. The aim of the review is to describe what is currently known about the association between Down syndrome and thyroid dysfunction.

Down syndrome, insulin-dependent diabetes mellitus and hyperthyroidism: a rare association

The association between Down syndrome (DS) and autoimmune endocrinopathies is well established. These disorders become increasingly frequent as children grow older and the onset of one often predisposes to the development of others. However, there are few cases in the literature reporting the simultaneous onset of type 1 diabetes mellitus and hyperthyroidism in children with DS. We describe a case of an 8-year-old girl with DS who presented at the emergency department with hyperglycaemia and ketosis as a primary manifestation of type 1 diabetes mellitus. During the initial investigation, hyperthyroidism was detected, with thyroid-stimulating hormone<0.01 µUI/mL, positive antithyroid antibodies and an increase in thyroid gland on ultrasound. The authors present this case to underline the usefulness of monitoring thyroid function at the diagnosis of diabetes, even without apparent clinical manifestations, and to alert for the possibility of autoimmune endocrine dysfunction in children with DS.

Down syndrome and thyroid function

Thyroid dysfunction in children with Down syndrome (DS) can occur as early as birth. As children with DS age, their risk for thyroid autoimmunity manifested as autoimmune hypothyroidism or Graves disease increases. The optimal timing and method for thyroid screening in children with DS remains controversial. The American Academy of Pediatrics recommends annual screening in this population. Consensus is needed to establish working definitions of euthyroidism and mild hypothyroidism in all infants, but especially in those with DS.

Fifteen-year follow-up of thyroid status in adults with Down syndrome

BACKGROUND

The natural history of thyroid function in adults with Down syndrome is relatively unknown with limited long-term follow-up data.

METHOD

This study investigated annual thyroid function tests in 200 adults with Down syndrome over a 15-year period.

RESULTS

For healthy adults with Down syndrome there is a gradual increase in thyroxine and possible gradual decline in thyroid-stimulating hormone with age. The 15-year incidence for definite hypothyroidism remains low and subclinical hypothyroidism is not a precursor for the onset of definite hypothyroidism.

CONCLUSIONS

The incidence of thyroid dysfunction is markedly less than would be expected from prevalence studies. Subclinical hypothyroidism is not necessarily a precursor to definite hypothyroidism. Prevalence studies have overstated the association between thyroid dysfunction and Down syndrome. Routine screening for adults with Down syndrome who are euthyroid can be reduced to every 5 years rather than the 1-2 years, as is the present policy.

Increase in incidence of medically treated thyroid disease in children with Down Syndrome after rerelease of American Academy of Pediatrics Health Supervision guidelines

OBJECTIVE

The purpose of this work was to estimate the incidence of medically treated thyroid disease in children with Down syndrome enrolled in Tennessee Medicaid (TennCare) during 1995-2005 and to determine whether rates increased after rerelease of American Academy of Pediatrics guidelines in 2001.

PATIENTS AND METHODS

We conducted a population-based retrospective cohort study in which we identified children with Down syndrome by using TennCare files and birth certificates. We included 1- to 18-year-olds who were continuously enrolled in TennCare and did not fill a prescription for thyroid medication during a 90-day prestudy period. The rate of medically treated thyroid disease (prescription filled for thyroid medication) was the main outcome. We used Poisson regression to estimate rates of medically treated thyroid disease according to study year, age, gender, race, region of residence, and payer type.

RESULTS

During the 11-year study period, 1257 children with Down syndrome (28% black, 72% white) met inclusion criteria. Overall, 10.8% filled a new prescription for thyroid medication. Rates of medically treated thyroid disease per 1000 child-years were 13.25 (1995-1997), 13.34 (1998-1999), 13.62 (2000-2001), 22.37 (2002-2003), and 22.51 (2004-2005). After adjusting for child age and race, there was an increased rate of medically treated thyroid disease in 2002-2003 and 2004-2005 compared with 1995-1997. In a comparison cohort of children without Down syndrome, there was a smaller increase in the rate of medically treated thyroid disease when comparing 2002-2003 and 2004-2005 with 1995-1997.

CONCLUSIONS

Over the 11-year period, 10.8% of children with Down syndrome filled a new prescription for a thyroid medication. A 73% increase in the incidence of medically treated thyroid disease occurred after rerelease of American Academy of Pediatrics guidelines, which may have influenced screening.

Successful aging in a 70-year-old man with down syndrome: a case study

The authors present a case study of a 70-year-old man with Down syndrome ("Mr. C.") who they followed for 16 years and who does not exhibit declines in cognitive or functional capacities indicative of dementia, despite having well-documented, complete trisomy 21. The authors describe the age-associated changes that occurred over 16 years as well as provide detailed information regarding Mr. C.'s health and genetic status. To further emphasize Mr. C.'s successful aging, the authors compared his longitudinal performance profile with that of 2 peers of comparable level of intellectual functioning: 1 similar-aged man with clinical Alzheimer's disease and a younger man who was healthy. The authors present potential explanations for the phenotypic variability observed in individuals with Down syndrome.

Thyroid dysfunction in Down's syndrome and screening for hypothyroidism in children and adolescents using capillary TSH measurement

Thyroid dysfunction is more common in individuals with Down's syndrome (DS) than in the general population, whose clinical features can mask the presenting signs and symptoms of hypothyroidism. Biochemical screening is necessary; however, venepuncture may be difficult.

AIMS

To assess the prevalence of thyroid dysfunction in children and adolescents with DS and the feasibility of screening for hypothyroidism using capillary dried blood spot thyroid stimulating hormone (TSH) from infancy.

METHODS

394 children (217 boys, 177 girls) were clinically assessed for thyroid dysfunction and 305 children (aged 4 months to 18.9 years) were screened for hypothyroidism by capillary whole blood TSH sample.

RESULTS

Thyroid dysfunction was detected in 4.6%, with 50% unscreened since neonatal screening. Parents reported minimal distress by fingerprick screening.

CONCLUSION

DS is associated with an increased prevalence of thyroid dysfunction, particularly in preschool children. Biochemical screening is essential and capillary whole blood TSH sampling for hypothyroidism is feasible, less invasive and acceptable.

Natural history of thyroid function in adults with Down syndrome--10-year follow-up study

BACKGROUND

The natural history of thyroid function in adults with Down syndrome (DS) is unknown.

METHOD

This study investigated annual thyroid function tests in 200 adults with DS over a 10-year period.

RESULTS

Transient and persistent thyroid dysfunction was common. The 5- and 10-year incidence of definite hypothyroidism was 0.9%-1.64% and 13.6%, respectively. Subclinical hypothyroidism was not found to be an early sign for definite hypothyroidism.

CONCLUSIONS

Routine screening for adults with DS who are euthyroid can be reduced to every 5 years rather than the present policy of every 1-2 years.

Longitudinal study of thyroid function in Down's syndrome in the first two decades

AIMS AND METHODS

Thyroid function tests were initially carried out on 122 children with Down's syndrome aged 6-14 years and then repeated four to six years later in 103 adolescents (85% of the group of 122) when they were aged 10-20 years (median 14.4 years). At the second test two were hypothyroid and two with isolated raised thyroid stimulating hormone (IR-TSH) were receiving thyroxine.

RESULTS

At the first test there were 98 (80%) euthyroid children: 83 were retested and four (5%) had IR-TSH. At the first test 24 had IR-TSH: 20 were retested and 14 (70%) had become normal. Seventeen with IR-TSH on initial testing had a thyrotrophin releasing hormone test within three months; TSH had become normal in eight (47%) of these children. There was no association between reported clinical symptoms and IR-TSH, but there were clear symptoms in one of the two with definite hypothyroidism.

CONCLUSIONS

The likelihood ratio for a positive result on second testing when raised TSH and positive antibody status on first testing are combined is 20. This suggests initial testing results could be used as a basis to select a subgroup for further testing at say five yearly intervals unless new symptoms emerge in the interim. It also suggests that yearly screening (as recommended by the American Academy of Pediatrics, 2001) is probably not justified in the first 20 years of life.

[Graves' disease in patients with Down syndrome]

Three patients showing the rare association of Down syndrome and Graves' disease are reported. While two of the patients were asymptomatic, the third showed goiter, nervousness, weight loss, and tachycardia. In addition to the typical features of hyperthyroidism, this patient showed right heart failure and hypertransaminasemia, which disappeared with antithyroid treatment. Because Graves' disease is rare in children, and the clinical presentation was unusual in one of our patients, we report three patients with Graves' disease and Down syndrome, and emphasize the importance of periodic evaluation of thyroid function in children with Down syndrome not only to detect hypothyroidism.

The genetics of Hashimoto's disease

Despite strong epidemiologic evidence in favor of a genetic component in the etiology of HT, few hereditary risk factors have been consistently identified. These factors include the HLA and CTLA-4 genes. The mechanisms by which these genes confer increased susceptibility to HT are unclear. The identification of these genes has failed to explain completely the large hereditary effect observed in families of patients. More substantial genetic determinants must be hidden in the folds of the human genome and will most likely be detected in the near future. The powerful approach of linkage analysis will be supported by advancements in the description of the human genome and by technologic improvements in the ability to process large amounts of biologic data. Knowledge of such determinants will provide predictive tools to be used on clinical grounds and invaluable insight into the pathogenesis of this puzzling disease.