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Ataxia-telangiectasia (A-T) - Patients develop progressive cerebellar ataxia by around the second year of life - patients are generally wheelchair bound after 10 years of age.  The ataxia typically precedes the development of cutaneous telangiectasias.  Other neurologic abnormalities include oculomotor apraxia, dysarthria, and choreoathetosis.  Older patients with Ataxia-Telangiectasia can develop cerebellar atrophy which can be a helpful clue for making a proper diagnosis.  



Ataxia-Telangiectasia like disorder


Ataxia-telangiectasia like disorder (ATLD) -  Patients also develop progressive cerebellar ataxia.  However, despite the name, these patients do not develop cutaneous telangiectasias.  


Dyskeratosis Congenita


Dyskeratosis congenita (Hoyeraal-Hreidarsson syndrome) - Patients with the severe infant-onset form of disease can have ataxia due to cerebellar hypoplasia.  Additional features include IUGR, severe enteropathy, failure to thrive, and a combined immunodeficiency.  



PNP Deficiency


PNP deficiency - The majority (2/3) patients develop early onset neurological abnormalities: these can include ataxia, mental retardation, spasticity, tremor, and hyperactivity.



Mevalonic Aciduria


Mevalonic aciduria - Patients are chacterized by recurrent febrile episodes similar to hyper IgD syndrome.  However, these patients also exhibit dysmorphic facial features (microcephaly, low-set posteriorly rotated ears, down slanted palpebral fissures), ataxia, mental retardation, cataracts, and failure to thrive.  Patients have greatly elevated mevalonic acid levels in the urine during and between attacks.   



Biotinidase Deficiency


Biotinidase deficiency - This condition results in impaired humoral and cell-mediated immunity.  Mucocutaneous candidiasis and systemic bacterial/viral infections occur.  Neurologic features include seizures, developmental delay, ataxia, and hypotonia.  Dermatitis, alopecia, and candidiasis also occur. The symptoms improve with dietary biotin supplementation.  



Chediak-Higashi Syndrome


Chediak-Higashi syndrome - Patients develop neurologic abnormalities including peripheral neuropathy (causing weakness and sensory deficits), cerebellar ataxia, seizures, cranial nerve palsies, and developmental delay.  Older patients who survive to the second or third decade may require a wheelchair due to poor balance and weakness. 



Griscelli Syndrome Type 2


Griscelli syndrome type 2 - Patients may have neurologic abnormalities such as ataxia, seizures, dysarthria, hemiplegia, and developmental delay. This disease is also characterized by mild neutropenia, impaired CD8 and NK cell cytotoxicity, oculocutaneous hypopigmentation, and a predisposition to develop hemophagocytic lymphohistiocytosis. 

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