The phenotypic spectrum of ataxia-telangiectasia (A-T), a multisystem disorder, is a continuum ranging from classic A-T at the severe end and variant A-T at the milder end. Nonetheless, distinguishing between classic A-T and variant A-T on this spectrum helps understand differences in disease course, rate of progression, and life expectancy. Classic A-T is characterized by childhood onset of progressive neurologic manifestations (initially cerebellar ataxia, followed typically by extrapyramidal involvement and peripheral sensorimotor neuropathy), immunodeficiency (variably associated with abnormalities of humoral immunity, cellular immunity, or combined immune deficiency), pulmonary disease (resulting from recurrent infections, immune deficiency, aspiration, interstitial lung disease, and neurologic abnormalities), and increased risk of malignancy. Although it is generally accepted that intellectual disability is not common in A-T, disturbances in cerebellar as well as non-cerebellar brain areas and networks may result in cognitive deficits. Increased sensitivity to ionizing radiation (x-ray and gamma ray) can result in severe side effects from such treatments. Life expectancy is significantly reduced due to cancer, pulmonary disease, and infections. Variant A-T has a significantly milder disease course. While cerebellar ataxia can be absent, extrapyramidal movement disorders are common (typically dystonia and dystonic tremor) and most individuals have manifestations of axonal sensorimotor polyneuropathy. In contrast to classic A-T, immune function is generally normal, respiratory infections are not increased, and pulmonary disease is not a major feature. However, risk of developing malignancies is increased, particularly in premenopausal females who have an increased risk of developing breast cancer and hematologic malignancies.

Male patients with hypogonadotropic hypogonadism due to isolated luteinizing hormone (LH) deficiency have normal sexual differentiation but fail to develop spontaneous puberty. Absence of LH alters Leydig cell proliferation and maturation and impairs the onset of normal spermatogenesis, which requires high levels of intratesticular testosterone. Infertility and very low levels of spermatogenesis generally persist in affected men despite long-term exposure to gonadotropin therapy. Female patients exhibit normal pubertal development and menarche, followed by oligomenorrhea and anovulatory secondary amenorrhea (summary by Basciani et al., 2012). Congenital idiopathic hypogonadotropic hypogonadism (IHH) is a disorder characterized by absent or incomplete sexual maturation by the age of 18 years, in conjunction with low levels of circulating gonadotropins and testosterone and no other abnormalities of the hypothalamic-pituitary axis. Idiopathic hypogonadotropic hypogonadism can be caused by an isolated defect in gonadotropin-releasing hormone (GNRH; 152760) release, action, or both. Other associated nonreproductive phenotypes, such as anosmia, cleft palate, and sensorineural hearing loss, occur with variable frequency. In the presence of anosmia, idiopathic hypogonadotropic hypogonadism has been called 'Kallmann syndrome (KS),' whereas in the presence of a normal sense of smell, it has been termed 'normosmic idiopathic hypogonadotropic hypogonadism (nIHH)' (summary by Raivio et al., 2007). Because families have been found to segregate both KS and nIHH, the disorder is here referred to as 'hypogonadotropic hypogonadism with or without anosmia (HH).' For a general phenotypic description and discussion of genetic heterogeneity of hypogonadotropic hypogonadism, see 147950. Reviews Arnhold et al. (2009) noted that the clinical manifestations of female patients with hypogonadotropic hypogonadism due to mutations in LHB are very similar to those of women with hypergonadotropic hypogonadism due to inactivating mutations of the LH receptor (see 238320): all have female external genitalia, spontaneous development of normal pubic hair and breasts at puberty, and normal to late menarche followed by oligoamenorrhea and infertility. Pelvic ultrasound shows a small or normal uterus and normal or enlarged ovaries with cysts. However, women with LHB mutations can be treated with luteinizing hormone or chorionic gonadotropin (CG; 118860) replacement therapy; women with LH receptor mutations are resistant to LH, and no treatment is effective in recovering their fertility.

STRC-related autosomal recessive hearing loss (STRC-HL) comprises both nonsyndromic sensorineural hearing loss and sensorineural hearing loss with decreased fertility in males who have biallelic contiguous gene deletions involving STRC and CATSPER2. The hearing loss is mild to moderate, congenital, bilateral, and symmetric. Mean pure tone hearing loss averages 40-50 decibels (dB) at the time of diagnosis; hearing loss is not severe to profound in children or young adults. Of note, while many newborns with STRC-HL will be identified by newborn hearing screening (NBHS), some newborns with STRC-HL will not because some screening methods may not detect milder hearing loss. Males with biallelic contiguous gene deletions involving STRC and CATSPER2 are at risk for CATSPER2-related male infertility due to morphologic sperm abnormalities that affect sperm motility. In contrast, females with contiguous gene deletions do not have related fertility issues.