**Table 1.**

*Clinical and laboratory features of rare genetic disorders that can be discriminate with A-T.*

### *Ataxia Telangiectasia DOI: http://dx.doi.org/10.5772/intechopen.112005*

serum AFP levels in most people with AT remains unknown. Assessment of AFP levels can be a helpful tool in the early diagnosis of AT [45].

As the whole exome sequencing becomes increasingly standard clinical practice for individuals with unusual and/or unexplained symptoms, it is likely that more people with mild forms of AT will be diagnosed [136]. This will necessarily change our views on the phenotypic expression of AT. Prenatal genetic diagnosis is possible when prospective parents each have confirmed pathogenetic mutations in ATM. Preimplantation genetic diagnosis (PGD) can avoid the birth of an affected child in parents who have an affected child (or children) with AT. At least two such cases have been described in the literature so far [137, 138].

Additionally, the newborn screening (NBS) test for severe combined immunodeficiency (SCID), introduced in recent years, can identify children born with other immunodeficiencies, including AT, which involve a deficiency or absence of T and B lymphocytes [139, 140]. Despite the lack of effective treatments for AT, early diagnosis allows for genetic counseling and family education, as well as intensive supportive care. Genetic counseling can provide AT genetic testing for siblings and other family members and help interpret test results.

Differential diagnosis. There are some rare disorders that can be misdiagnosis with AT based on similar clinical and laboratory features. The most common disorders that are sometimes confused with AT are: cerebral palsy (CP) and Friedreich's ataxia (FA or FRDA). Each of these diseases can be distinguished from AT based on neurological examination and clinical history. CP, unlike AT, is a nonprogressive motor dysfunction resulting from early brain injury [141]. In addition, most children with CP manifest regional or diffuse spasticity in a pattern not seen in AT. Children with ataxia due to CP will not manifest laboratory abnormalities associated with AT. In FRDA, symptoms usually tend to present later between the ages of 10 and 16 and differ from AT in the absence of telangiectasias and oculomotor apraxia, the early absence of tendon reflexes, a normal AFP, the frequent presence of scoliosis, cardiomyopathy, and abnormal ECG features [84, 142].

Other disorders with childhood-onset ataxia include ataxia telangiectasia like disorder 2 (ATLD2), ataxia oculomotor apraxia type 1 (AOA1), ataxia oculomotor apraxia type 2 (AOA2), radiosensitivity, immunodeficiency, dysmorphic features, and learning difficulties (RIDDLE) syndrome (RNF168 deficiency), and spinocerebellar ataxia with axonal neuropathy (SCAN1).

Immunodeficiency is one of the common symptoms of Nijmegen breakage syndrome (NBS, with birds like face and microcephaly), ataxia telangiectasia like disorder 1 (ATLD1, due to meiotic recombination 11 homolog A (MRE11) deficiency), and RIDDLE syndrome that can be confused with AT. As in AT, elevated serum AFP levels are also present in AOA2 and RIDDLE syndrome. Therefore, knowledge of the gene mutation in a child with ataxia, immunodeficiency, telangiectasias, radiosensitivity, and elevated AFP can distinguish AT from other disorders with ataxia of childhood onset [11, 143]. A comparison of the clinical and laboratory features of these disorders is shown in **Table 1**.
