Allan–Herndon–Dudley syndrome (AHDS)- this syndrome is characterized by congenital hypotonia that progresses to spasticity, poor head control ,dystonia , severe psychomotor delays ,muscle hypoplasia, generalized muscle weakness, and limited speech.
Importantly, these patients have elevated serum levels of free T3, low to below normal serum levels of free T4, and levels of thyroid stimulating hormone that are within the normal range.
The active form of thyroid hormone is T3, which binds to nuclear receptors.
The cellular influx and efflux of thyroid hormones are facilitated by transmembrane protein transporters. Of these transporters, monocarboxylate transporter 8 (MCT8) is the only one specific for the
transport of thyroid hormones and some of their derivatives.
Mutations in SLC16A2, the gene that encodes MCT8, lead to an X‑linked syndrome(Xq13) with severe neurological impairment and altered concentrations of thyroid hormones. MCT8 is highly expressed in liver and brain. Recent evidence has suggested that monocarboxylate transporter 8 (MCT8) is important for T3 uptake into central neurons. Loss-of-function mutations in this gene have been reported worldwide in patients with X-linked mental retardation (XLMR-AHDS)
6 patient was reported in WOlfSON hospital with marked hypotonia ,spasticity ,poor head control and dystonia All of them had developmental delay and disturbed Thyroid function that showed the typical pattern of MCT8 deficiency .Mutation on MCT8 gene was proven in all of them.This cases highlights the importance of determining TH levels ,especially T3,in patients wth early postnatal hypotonia,dystonia, and spasticity
