Ataxia telangiectasia variant V1




Ataxia telangiectasia variant V1 is a very rare syndrome presenting at birth with microcephaly, dysmorphic facial features, becoming more noticeable with age, growth delay, and later-onset complications such as malignancies and infections. Also, it is a condition characterized by short stature, an unusually small head size (microcephaly), distinctive facial features, recurrent respiratory tract infections, an increased risk of cancer, intellectual disability, and other health problems.


  • Abnormal hair quantity
  • Abnormal immunoglobulin level
  • Abnormal nasal morphology
  • Abnormality of chromosome stability
  • Abnormality of the upper urinary tract
  • Attention deficit hyperactivity disorder
  • Cognitive impairment
  • Convex nasal ridge
  • Decreased body weight
  • Deep philtrum
  • Depressed nasal bridge
  • Hearing abnormality
  • Hemolytic anemia
  • Low anterior hairline
  • Malabsorption
  • Microcephaly
  • Recurrent respiratory infections
  • Short neck
  • Short stature
  • Sinusitis
  • Sloping forehead
  • Thrombocytopenia
  • Upslanted palpebral fissure
  • Urogenital fistula
  • Microcephaly
  • Prominent midface emphasized by sloping forehead and receding mandible
  • Upwardly slanted palpebral fissures
  • Long and beaked nose or short nose with anteverted upturned nostrils
  • Clefted lip/palate or choanal atresia has been described
  • Mild growth retardation
  • Premature ovarian insufficiency is common in females with the condition
  • Minor skeletal anomalies such as clinodactyly of the 5th fingers and partial syndactyly of the 2nd and 3rd toes (50% of patients)
  • Delayed speech development
  • Hair is usually sparse and thin in infancy but improves with age
  • Hair greying can appear as early as in 2nd or 3rd decade
  • Congenital renal anomalies (hypoplasia/aplasia, horseshoe or double kidney, ectopic/dystopid kidneys)
  • Immune deficiency with recurrent respiratory tract infections
  • Predisposition to malignancies (predominantly lymphoid)


It is a rare autosomal recessive congenital disorder causing chromosomal instability, probably as a result of a defect in the Double Holliday junction DNA repair mechanism and/or the Synthesis Dependent Strand Annealing mechanism for repairing double strand breaks in DNA. It is caused by mutations in the NBN gene (8q21-q24) which leads to partially functional truncated fragments of nubrin, the gene product involved in repairing double stranded DNA breaks. 


Early diagnosis is important to avoid severe recurrent infections due to increased immunodeficiency. Avoid unncessary radiation exposure for diagnostic purposes, due to increased sensitivity to IR radiation. Molecular testing confirms diagnosis. 

Differential diagnosis includes Fanconi anemia, Bloom syndrome, NBS-like disorder, ataxia-telangectasia-like disorder, LIG4 syndrome, NHEJ1 syndrome, and Seckel syndrome. 


There is no specific treatment/therapy for NBS. 


  • NIH
  • Genetics Home Reference