1. SECTIONS:
2. preface & acknowledgements
3. genetics at a glance
4. contacts, support & testing
5. testing & pregnancy
6. newborn screening
7. cancer in the family
8. cardiovascular conditions
9. chromosomal conditions
10. clotting & bleeding conditions
11. cystic fibrosis
12. diabetes
13. fragile X syndrome and other causes of developmental delay
14. haemoglobinopathies
15. hereditary haemochromatosis
16. neurofibromatosis
17. neurological conditions
18. psychiatric conditions
19. genetics in practice
20. emerging genetic technologies
21. glossary

Primary congenital hypothyroidism

 

1. Affects approximately 1 in 4000 babies.
2. Primary hypothyroidism is due to an absent, ectopic or malfunctioning thyroid gland.
3. About 80% of cases result from an absent or ectopic thyroid. About 20% of cases are due to dyshormonogenesis, a collection of metabolic disorders affecting the production of thyroid hormone.
4. Congenital hypothyroidism is not usually inherited, but rather occurs sporadically. Therefore, other family members are not usually at increased risk.

 

Common clinical features

1. Newborns may be asymptomatic at birth. Early neonatal signs are prolonged jaundice (>7 days), umbilical hernia, constipation, macroglossia, feeding problems and hypotonia.
2. Without treatment, developmental delay and growth retardation occur. One form of dyshormonogenesis (Pendred syndrome) is associated with deafness.

 

Test

1. Thyroid stimulating hormone (TSH) is assayed by an immunoassay.
2. Elevated levels of TSH are an indication of primary hypothyroidism.
3. Further serum thyroid function tests are required for diagnosis. In addition, a thyroid scan and audiology test may be performed in some tertiary centres.
4. If the thyroid gland is normally sized and placed, transient hypothyroidism might be present, and follow-up testing may be recommended.

 

Treatment

1. Thyroxine is taken orally for life.
2. Regular blood tests are required to monitor thyroxine and TSH levels.
3. Supervision by a paediatrician is recommended.

 

Implications for other family members

1. 95% of these cases occur sporadically and subsequent pregnancies are not at increased risk.
2. 5% of cases are due to a single mutation. These are inherited as autosomal recessive conditions with a 1 in 4 risk of recurrence in subsequent pregnancies.

 

Other amino acidopathies:

1. These conditions result from other defects in the metabolism of amino acids in which organic acids are not produced. This may be a defect in a transporter or an enzyme of amino acid metabolism.
2. These conditions are rare but can be life threatening.
3. Treatment consists of a low-protein diet, supplements and medications.
4. Early treatment is associated with reduced mortality and morbidity.

 

Test

1. Mass spectometry is used to detect abnormal metabolites in the blood.
2. Results are usually available within 24 to 48 hours of sample receipt at the laboratory.
3. Additional testing may be necessary for confirmation of diagnosis.

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