Clinical diagnosis and genetic counseling of atypical ataxia‑telangiectasia in a Chinese family.

Ataxia‑telangiectasia (A‑T) is an autosomal recessive chromosome breakage disorder caused by mutations in the ATM serine/threonine kinase (ATM) gene. Typically, it presents in early childhood with progressive cerebellar dysfunction, accompanied by immunodeficiency and oculocutaneous telangiectasia. In the present study, the clinical and genetic findings of a Chinese family affected with A‑T in two live siblings, the proband (II‑2) and his elder brother (II‑1), as well as a fetus (II‑3) were reported. General health, clinical neurological, electrophysiological (motor and sensory nerve conduction) and magnetic resonance imaging evaluations revealed that patients II‑1 and II‑2 had similar symptoms of ataxia, dysarthria, conjunctival hyperemia and elevated serum α‑fetoprotein, whereas patient II‑1 had earlier A‑T onset at 2 years old and more serious problems with movement and intelligence. Targeted sequencing followed by Sanger sequencing revealed that these two patients carried the compound heterozygotes of a novel nonsense mutation c.5170G>T (p.Glu1724Ter) and a known nonsense mutation c.748C>T (p.Arg250Ter) in the ATM gene. Each mutation was inherited from an asymptomatic parent, which therefore confirmed the diagnosis of A‑T. Given this, proband's mother performed prenatal diagnosis in her third pregnancy. Unfortunately, the fetus had the same causal mutations as its siblings and the pregnancy was terminated. The findings of the present study expanded the mutation spectrum of the ATM gene and may help in understanding the genetic basis of A‑T, in order to guide genetic counseling and prenatal diagnosis.