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Synopsis: We report an adolescent girl with Down syndrome, who presented with hyperthyroidism. Autoimmune thyroid disorders may occur in children with Down syndrome, with hypothyroidism developing more frequently. Hyperthyroidism may also be associated with Down syndrome, and must not be missed.
Children with Down syndrome, or trisomy-21 may have coexistent autoimmune disorders (1,2). A variety of T cell abnormalities have been described in Down syndrome: increased Ia positive T cells and a premature increase in the 3G5 age related T cell subset (3). Among thyroid disorders, hypothyroidism has been reported more often than hyperthyroidism (4,5,6,7,8).
We describe a case of a girl with Down syndrome who presented with hyperthyroidism.
Case report: A 15 year old girl of Down syndrome diagnosed in the neonatal period, presented with symptoms of thyrotoxicosis: increased appetite, hair loss, difficulty in initiating sleep and lack of weight gain. A student of standard nine, her school performance had been adequate, except in mathematics. She attained menarche spontaneously, but had been amenorrheic for six months.
On examination, she had tachycardia (140 beats/min), a grade 1 goitre (35 gm), hand tremor and hyperkinesis. She had physical features of Down syndrome. Systemic examination was normal. Thyroid hormones were elevated: T3 3.1 ng/ml [N: 0.6-2.2 ng/ml], T4 18.4 ug/dl [N: 5-13 ug/dl] and TSH was 0.2 miu/ml [N: 0.3 -6.8 miu/ml]. 131 I radioiodine uptake was increased: 64% at two hours, 51% at 24 hours and 47% at 48 hours. Thyroid microsomal antibody was positive at 1:400 dilutions, and anti thyroglobulin antibody at 1:160. She was started on 25 mg of carbimazole a day with which there was clinical improvement. Her menstruation resumed, and she is euthyroid 12 months after initiation of antithyroid therapy.
Discussion: This girl with Down syndrome had the clinical, functional, biochemical and immunological features of hyperthyroidism. Most large series studying thyroid function in Down syndrome report that hypothyroidism is more common (4,5,6,7,8): only 1.4%(9) to 5% (6) of individuals with thyroid dysfunction have hyperthyroidism, whereas the prevalence of subclinical hypothyroidism is nearly 30% (7,10).
An Italian study showed that patients with Down syndrome who were positive for
antithyroid antibody were more likely to develop clinically evident thyroid
disease (5). This appears logical in view of the T cell abnormalities in Down
syndrome (3). In contrast, a five-year annual follow up study in Australia
suggested that thyroid dysfunction in Down syndrome may be related to
inappropriate TSH secretion, or thyroid insensitivity to TSH (3). Similarly, an
American study concluded that thyroid dysfunction in Down syndrome is a common
heterogeneous disorder, which cannot be solely explained by autoimmunity (6).
The few HLA studies in hyperthyroid individuals with Down syndrome reported the
presence of HLA BW46 (11), and HLA A3, A9, B8, B15, DR3, DR5 when other
autoimmune disorders coexisted (2).
In the past, attempts were made to correlate maternal thyroid disease causing Down syndrome in the offspring (12). Most recent studies have shown no such association (7).
In summary, children with Down syndrome must be screened for thyroid dysfunction,
starting early in life; though hypothyroidism is more common, hyperthyroidism
can also occur, and must not be missed.
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