Question: Which hormone concentrations are altered in patients with the Allan–Herndon–Dudley syndrome?

Context:
This syndrome is characterized by axial hypotonia, severe mental retardation, dysarthria, athetoid movements, spastic paraplegia, and a typical thyroid hormone profile. 
Our case and the review of the pertinent literature suggest that Allan-Herndon-Dudley syndrome should be suspected in males with the typical neurological and thyroid profile, even in cases with normal brain myelination.
Allan-Herndon-Dudley Syndrome (AHDS), an X linked condition, is characterized by congenital hypotonia that progresses to spasticity with severe psychomotor delays, in combination with altered thyroid hormone levels, in particular, high serum T3 levels. 
Mutations in the MCT8 gene are associated with Allan-Herndon-Dudley Syndrome (AHDS), consisting of severe psychomotor retardation and disturbed TH parameters.
Allan-Herndon-Dudley syndrome (AHDS), an X linked condition, is characterized by severe intellectual disability, dysarthria, athetoid movements, muscle hypoplasia and spastic paraplegia in combination with altered TH levels, in particular, high serum T3 levels. 
In two generations its presence was detected in the hemizygous state in two males with neurological abnormalities including mental retardation, axial hypotonia, hypertonia of arms and legs and athetoid movements. One of them presented normal thyroid hormone levels. 
Our results show the difficulty of distinguishing AHDS from patients with X-linked intellectual disability solely on the basis of clinical features and biochemical tests, and we advise screening for MCT8 mutations in either young or older patients with severe intellectual disability, axial hypotonia/dystonia, poor head control, spastic paraplegia, and athetoid movements even when they have normal thyroid hormone profiles.
Hemizygous MCT8 mutations in males cause severe psychomotor retardation, known as the Allan-Herndon-Dudley syndrome (AHDS), and abnormal serum TH levels.
Allan-Herndon-Dudley syndrome (AHDS) is a severe psychomotor retardation characterized by neurological impairment and abnormal thyroid hormone (TH) levels. 
The hallmarks of Allan-Herndon-Dudley syndrome, caused by MCT8 mutations, are severe psychomotor retardation and elevated T(3) levels.
Inactivating mutations in the gene encoding MCT8 are associated with a severe form of psychomotor retardation and abnormal serum TH levels (Allan-Herndon-Dudley syndrome). 
Mutations of this transporter determine a distinct X-linked psychomotor retardation syndrome (Allan-Herndon-Dudley syndrome (AHDS)) that is attributed to disturbed thyroid hormone levels, especially elevated T(3) levels.
This syndrome is characterized by abnormally high T3, low/normal T4 serum levels and slightly elevated serum TSH.
High D1 activity in liver and kidney increases T4 and rT3 deiodination, and contributes to the increased serum T3.
One of these, monocarboxylate transporter 8 (MCT8) is mutated in Allan-Herndon-Dudley syndrome, a severe mental retardation associated with abnormal thyroid hormone constellations. 
The endocrine phenotype showed low serum total and free thyroxine (T4), very elevated total and free triiodothyronine (T3) and normal thyrotropin (TSH) with blunted response to thyrotropin-releasing hormone (TRH). 
Monocarboxylate transporter 8 (MCT8, SLC16A2) is a thyroid hormone (TH) transmembrane transport protein mutated in Allan-Herndon-Dudley syndrome, a severe X-linked psychomotor retardation. 
The clinical importance of TH transporters is dramatically shown in patients with mutations in MCT8, suffering from severe X-linked psychomotor retardation in combination with disturbed TH levels, especially high serum T(3) levels, now referred as Allan-Herndon-Dudley Syndrome (AHDS). 
Therefore, the criterion for MCT8 mutation screening in these patients is the profile of increased T(3) and low-normal to low FT(4) serum levels.
However, T3 level was elevated.
AIM: Mutations in the SLC16A2 gene have been implicated in Allan-Herndon-Dudley syndrome (AHDS), an X-linked learning disability* syndrome associated with thyroid function test (TFT) abnormalities.
Dystonic cerebral palsy was the most common initial clinical diagnosis, and AHDS was suspected only retrospectively, considering the characteristically abnormal thyroid function tests, with high serum tri-iodothyronine (T(3)), as the most consistent finding.
Although dysmorphic features suggestive of AHDS are not always present, T(3) measurement is a reliable screening test.
Mutations in one of these, monocarboxylate transporter 8 (MCT8), have been identified as underlying cause for the Allan-Herndon-Dudley syndrome, an X-linked mental retardation in which the patients also present with abnormally high 3',3,5-triiodothyronine (T(3)) plasma levels.
With the discovery of monocarboxylate transporter 8 (MCT8) as a specific thyroid hormone transporter and the finding that mutations in this transporter lead to a syndrome of severe psychomotor retardation and elevated serum 3,3',5-tri-iodothyronine levels known as the Allan-Herndon-Dudley syndrome, the interest in this area of research has greatly increased. 
Elevated serum triiodothyronine and intellectual and motor disability with paroxysmal dyskinesia caused by a monocarboxylate transporter 8 gene mutation.
Additionally, the patient has a lesion in the left putamen region revealed by magnetic resonance imaging and elevated serum T3 levels.
The identified MCT8 gene mutation (R271H) is very likely to be the genetic cause for neuronal hypothyroidism despite elevated serum T3 levels.
Abnormal transport function is reflected by elevated free T3 and decreased free T4 levels along with clinical features characterized by neurological abnormalities including global developmental delay, central hypotonia, rotatory nystagmus, impaired hearing, spasticity and contractures of joints. We report a child with classical clinical features along with confirmatory deranged thyroid levels in blood.
Consistent with previous reports on MCT8 missense changes, the patient with c.1673G>A showed elevated serum T3 level. 
Moreover, we characterized a de novo translocation t(X;9)(q13.2;p24) in a female patient with full blown AHDS clinical features including elevated serum T3 levels.
Taken together, these data indicate that MCT8 mutations are not common in non-AHDS MR patients yet they support that elevated serum T3 levels can be indicative for AHDS and that AHDS clinical features can be present in female MCT8 mutation carriers whenever there is unfavorable nonrandom X-inactivation.
Endocrine functions other than thyroid hormone regulation and metabolism were intact, resulting in normal hypothalamic/pituitary function tests.
Conclusion: the characteristic thyroid hormone function tests and brain MRI findings may allow screening of high-risk populations for a better understanding of MCT8 pathophysiology.
Importantly, these patients have elevated serum levels of free T(3), low to below normal serum levels of free T(4), and levels of thyroid stimulating hormone that are within the normal range.
Pathogenic mutations in the MCT8 gene, which encodes a thyroid hormone transporter, results in elevated serum triiodothyronine (T3) levels, which were confirmed in four affected males of this family, while normal levels were found among obligate carriers.
In addition, the severe muscle hypoplasia observed in most AHDS patients may be a consequence of high serum T3 levels.
Abnormal transporter function is reflected in elevated free triiodothyronine and lowered free thyroxine levels in the blood. 
Mct8 transports thyroid hormones (T4 and T3), and the Allan-Herndon-Dudley syndrome is likely caused by lack of T3 transport to neurons during critical periods of fetal brain development. 

Answer: Thyroid hormone concentrations are altered in patients with the Allan-Herndon-Dudley syndrome. In particular, high serum T3 levels and low-normal to low T4 serum levels are common in the Allan-Herndon-Dudley syndrome. It is, an X linked condition, is characterized by severe intellectual disability, dysarthria, athetoid movements, muscle hypoplasia and spastic paraplegia in combination.
Exact answer: Thyroid