Classic Ataxia-Telangiectasia
The primary features of classic A-T:
Progressive gait and truncal ataxia with onset between ages one and four years
Progressively slurred speech
Oculomotor apraxia (inability to follow an object across visual fields)
Choreoathetosis (writhing movements)
Oculocutaneous telangiectasia (usually evident by age 6 years)
Frequent infections (with accompanying evidence of serum and cellular immunodeficiencies)
Hypersensitivity to ionizing radiation with increased susceptibility to cancer (usually leukemia or lymphoma)
Other features:
Premature aging with strands of gray hair
Endocrine abnormalities including insulin-resistant diabetes mellitus and premature ovarian failure (i.e., normal menarche followed by irregular menses and loss of ovarian function before age 40 years) [Author, personal observation]
Although the clinical manifestations of A-T in its late stages vary little from family to family, the age of onset and rate of progression can vary considerably even within a family with multiple affected individuals. For clinical reviews, see Boder [1985], Woods & Taylor [1992], Gatti [2001], Taylor & Byrd [2005], and Verhagen et al [2012].
Neurologic. The most obvious characteristic of classic A-T is progressive cerebellar ataxia. Shortly after learning to walk, children with A-T begin to stagger. Although the neurologic status of some children appears to improve from age two to four years, ataxia subsequently progresses. (The transient improvement is probably attributable to the rapid learning curve of young children.)
The ataxia begins as purely truncal but within several years involves peripheral coordination as well. Writing and drawing are affected by age five years.
By age ten years, most children become confined to a wheelchair.
Slurred speech and oculomotor apraxia are noted early. Both horizontal and vertical saccadic eye movements are affected [Farr et al 2002, Onodera 2006, Yakusheva et al 2007]. Drooling is common.
Choreoathetosis is found in almost all individuals with A-T. Myoclonic jerking and intention tremors are present in about 25%.
All teenagers with classic A-T need help with dressing, eating, washing, and toileting.
Muscle strength is normal at first but wanes with disuse, especially in the legs. Contractures in the fingers and toes are common in older individuals. Deep tendon reflexes are decreased or absent in older individuals; plantar reflexes are upgoing or absent
Intelligence is typically normal; however, learning difficulties are common. Slow motor and verbal responses make it difficult for individuals to complete "timed" IQ tests. Many American and British individuals with classic A-T have finished high school with good grades; some have finished college or university, often with the assistance of aides and attentive parents and sibs.
Dystonia and adult-onset spinal muscular atrophy have also been observed (see Non-Classic Forms of Ataxia-Telangiectasia).
Immunodeficiency, present in 60%-80% of individuals with classic A-T, is variable and does not correlate well with the frequency, severity, or spectrum of infections. The most consistent immunodeficiency reported in classic A-T is poor antibody response to pneumococcal polysaccharide vaccines [Sanal et al 1999, Nowak-Wegrzyn et al 2004]. Serum concentration of the immunoglobulins IgA, IgE, and IgG2 is often reduced. NK lymphocyte levels are occasionally elevated, most notably in individuals from Costa Rica [Regueiro et al 2000].
The immunodeficiency is not progressive, and some evidence suggests that T-cell lymphopenia may normalize after age 20 years [Boder 1985, Woods & Taylor 1992, Regueiro et al 2000, Gatti 2001, Pashankar et al 2006, Staples et al 2008].
Of note, immune status was more seriously impaired in 80 individuals with A-T and two null ATM alleles: both T- and B-cell lymphopenia and more frequent recurrent sinopulmonary infections were observed [Staples et al 2008]. Children with lymphopenia tend to have the most deleterious pathogenic variants, lowest (enzymatic) ATM kinase levels, most severe phenotypes, most frequent sinopulmonary infections, and poorest prognosis [Verhagen et al 2012].
Infection. In contrast to the spectrum of infection observed in most immunodeficiency disorders, the spectrum of infection in classic A-T does not include opportunistic infections. The frequency and severity of infections correlate more with ATM kinase levels and general nutritional status than with immune status.
Some individuals with classic A-T develop chronic bronchiectasis.
While individuals with frequent infections may occasionally benefit from prophylactic antibiotics and/or intravenous immunoglobulin (IVIG) replacement therapy [Nowak-Wegrzyn et al 2004], longevity has increased substantially even in those not receiving IVIG.
Pulmonary. In older individuals, pulmonary failure, with or without identifiable infections, is a major cause of failing health and death [Lockman et al 2012]. Life-threatening lymphocytic infiltration of the lung has been reported [Tangsinmankong et al 2001].
Other findings. Liver enzyme levels are often elevated in A-T, without apparent liver pathology. (Thus, liver biopsy is usually not revealing.)
Cancer. The risk for malignancy in individuals with classic A-T is 38%.
Leukemia and lymphoma account for about 85% of malignancies. Younger children tend to have acute lymphocytic leukemia (ALL) of T-cell origin and older children are likely to have an aggressive T-cell leukemia. Lymphomas are usually B-cell types.
As individuals with classic A-T are living longer, other cancers and tumors including ovarian cancer, breast cancer, gastric cancer, melanoma, leiomyomas, and sarcomas have also been observed.
Life expectancy. Over the past 25 years, for reasons that are unclear, the life expectancy of individuals with A-T has increased considerably. Most affected individuals now live beyond age 25 years. Some have survived into their 50s [Dörk et al 2004; Crawford et al 2006; Author, unpublished observations].
Pathology. The cerebellum atrophies early in the course of classic A-T, being visibly smaller on MRI by age seven or eight years, with concomitant loss of Purkinje cells and depletion of granule cells [Sardanelli et al 1995, Tavani et al 2003, Wallis et al 2007, Lin et al 2014].
At autopsy, virtually all affected individuals have a small embryonic-like thymus, lacking Hassall's corpuscles.
Microscopic nucleomegaly (i.e., irregular size and shape of nuclei) is a classic histologic characteristic of A-T cells and is used by pathologists in interpreting tissue changes in organs from persons with A-T. Nucleomegaly is easily appreciated in tissues where the architecture is otherwise very uniform, such as renal tubules and seminal ducts. Nucleomegaly most likely reflects perturbed cell cycle checkpoints and poor fidelity of DNA repair mechanisms and DNA processing.
Heterozygotes
The cancer risk of individuals heterozygous for an ATM pathogenic variant is approximately four times that of the general population, primarily because of the increased risk for breast cancer [Swift et al 1991, Stankovic et al 1998, Bretsky et al 2003, Bernstein et al 2006, Renwick et al 2006, Concannon et al 2008, Tavtigian et al 2009, van Os et al 2016].
Cancer risk probably depends on multiple factors including tumor type, age at cancer onset, and whether the individual is heterozygous for a missense or a truncating variant [Gatti 2001, Concannon 2002, Scott et al 2002, Spring et al 2002].
ATM variants associated with breast cancer tend to be missense changes whereas ATM missense variants in individuals with A-T only are uncommon (<10%) [Gatti et al 1999, Bernstein et al 2003, Tavtigian et al 2009]. Meta-analyses estimate a relative risk of three- to fourfold that in comparable general populations.
ATM pathogenic variants have been reported in both tumor cells and germline cells in several types of leukemia and lymphoma, including acute lymphoblastic leukemia (ALL), chronic lymphocytic leukemia (CLL), T-cell prolymphocytic leukemia (T-PLL), and mantle zone lymphoma [Stankovic et al 1998, Stilgenbauer et al 2000, Oguchi et al 2003, Eclache et al 2004].
T-cell ALL-associated ATM pathogenic variants are similar to those seen in individuals with A-T [Liberzon et al 2004, Pylkäs et al 2007].