PEDIATRICS Vol. 121 No. 1 January 2008, pp. e199-e202 (doi:10.1542/10.1542/peds.2007-1247)
EXPERIENCE & REASON |
A Novel Monocarboxylate Transporter 8 Gene Mutation as a Cause of Severe Neonatal Hypotonia and Developmental Delay
a Third Department of Pediatrics, University of Athens School of Medicine, Attikon University Hospital, Athens, Greece
b Departments of Medicine
d Pediatrics
e Committees on Genetics and Molecular Medicine, and J.P. Kennedy Mental Retardation and Developmental Disabilities Center, University of Chicago, Chicago, Illinois
c Neurology Department, Penteli Children's Hospital, Athens, Greece
ABSTRACT
Monocarboxylate transporter 8 acts as a specific cell membrane transporter for thyroxine and especially triiodothyronine into target cells. It is expressed in brain neurons and in many other tissues. The monocarboxylate transporter 8 gene resides on chromosome Xq13.2. An 11-month-old male infant was referred because of severe hypotonia from early life and global developmental delay. Thyroid-function tests showed normal thyrotropin levels and the characteristic for the disorder, including high serum triiodothyronine and low thyroxine concentrations. Molecular analysis of the monocarboxylate transporter 8 gene showed that the patient was hemizygous for a novel missense mutation P537L. This case highlights the importance of determining thyroid hormone levels, especially triiodothyronine, in infants with severe neonatal hypotonia.
Key Words: monocarboxylate transporter 8 neonatal hypotonia developmental delay thyroid hormones
Abbreviations: TH—thyroid hormone CNS—central nervous system T3—3,3',5-triiodothyronine D1—type 1 5'-deiodinase D2—type 2 5'-deiodinase T4—thyroxine rT3—3,3',5'-triiododothyronine MCT8—monocarboxylate transporter 8 TFT—thyroid-function test L-T4—L-thyroxine
Accepted May 24, 2007.
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