MedGen

Allan-Herndon-Dudley syndrome (AHDS), an X-linked disorder, is characterized in males by neurologic findings (hypotonia and feeding difficulties in infancy, developmental delay / intellectual disability ranging from mild to profound) and later-onset pyramidal signs, extrapyramidal findings (dystonia, choreoathetosis, paroxysmal movement disorder, hypokinesia, masked facies), and seizures, often with drug resistance. Additional findings can include dysthyroidism (manifest as poor weight gain, reduced muscle mass, and variable cold intolerance, sweating, elevated heart rate, and irritability) and pathognomonic thyroid test results. Most heterozygous females are not clinically affected but may have minor thyroid test abnormalities. [from GeneReviews]

Incomplete or underdevelopment of a tissue or organ. [from NCI]

Underdevelopment of the musculature. [from HPO]

Severe mental retardation is defined as an intelligence quotient (IQ) in the range of 20-34. [from HPO]

Inflammation of the thyroid gland. [from HPO]

A rare metabolic myopathy with characteristics of muscle cramping and/or stiffness after exercise (especially during heat exposure), post-exertional rhabdomyolysis and myoglobinuria and elevation of serum creatine kinase. Caused by mutation in the SLC16A1 gene. [from SNOMEDCT_US]

X-linked intellectual developmental disorder-100 (XLID100) is an X-linked recessive disorder characterized by a neurodevelopmental phenotype with impaired intellectual development with or without epilepsy. The phenotypic spectrum also includes hydrocephalus, either isolated or associated with other congenital anomalies, predominantly of the brain, kidneys, and urinary tract (summary by Kalantari et al., 2021). [from OMIM]

CASK disorders include a spectrum of phenotypes in both females and males. Two main types of clinical presentation are seen: Microcephaly with pontine and cerebellar hypoplasia (MICPCH), generally associated with pathogenic loss-of-function variants in CASK. X-linked intellectual disability (XLID) with or without nystagmus, generally associated with hypomorphic CASK pathogenic variants. MICPCH is typically seen in females with moderate-to-severe intellectual disability, progressive microcephaly with or without ophthalmologic anomalies, and sensorineural hearing loss. Most are able to sit independently; 20%-25% attain the ability to walk; language is nearly absent in most. Neurologic features may include axial hypotonia, hypertonia/spasticity of the extremities, and dystonia or other movement disorders. Nearly 40% have seizures by age ten years. Behaviors may include sleep disturbances, hand stereotypies, and self biting. MICPCH in males may occur with or without severe epileptic encephalopathy in addition to severe-to-profound developmental delay. When seizures are present they occur early and may be intractable. In individuals and families with milder (i.e., hypomorphic) pathogenic variants, the clinical phenotype is usually that of XLID with or without nystagmus and additional clinical features. Males have mild-to-severe intellectual disability, with or without nystagmus and other ocular features. Females typically have normal intelligence with some displaying mild-to-severe intellectual disability with or without ocular features. [from GeneReviews]