Clinical characteristics.

Nijmegen breakage syndrome (NBS) is characterized by progressive microcephaly, early growth deficiency that improves with age, recurrent respiratory infections, an increased risk for malignancy (primarily lymphoma), and premature ovarian failure in females. Developmental milestones are attained at the usual time during the first year; however, borderline delays in development and hyperactivity may be observed in early childhood. Intellectual abilities tend to decline over time. Recurrent pneumonia and bronchitis may result in respiratory failure and early death. Other reported malignancies include solid tumors (e.g., medulloblastoma, glioma, rhabdomyosarcoma).

Diagnosis/testing.

The diagnosis of NBS is established in a proband with characteristic clinical features and biallelic pathogenic variants in NBN on molecular genetic testing and/or absent nibrin protein on immunoblotting assay.

Management.

Treatment of manifestations: Standard antimicrobial therapies for infections; immunoglobulin replacement therapy in individuals with severe hypogammaglobulinemia and frequent infections; acellular vaccines; standard treatment of bronchiectasis and pulmonary infections; chemotherapy protocols for lymphoid malignancies adapted to individual tolerance; treatment of solid tumors adapted to individual tolerance; consideration of hematopoietic stem cell transplantation; hormone replacement therapy for females who have hypergonadotropic hypogonadism.

Surveillance:

• For affected individuals. Periodic follow up to monitor physical growth, infection frequency, and developmental progress; lifelong monitoring of immune biomarkers; monitor for malignancy and particularly in those with weight loss, fever, weakness, enlargement of peripheral lymph nodes, dyspnea, cough, and hepatosplenomegaly (assessment should be considered using ultrasonography, MRI, biopsy); monitor pubertal progression in both sexes and for premature ovarian insufficiency in females; monthly breast self-examination when hormone replacement therapy is administered; assess cognitive developmental and intellectual abilities before starting school and follow up periodically.
• For heterozygous adults. Monitor for malignancy, particularly breast cancer in women and prostate cancer in men.

Agents/circumstances to avoid: Because the cells from individuals with NBS are radiosensitive in vitro, doses of radiation used in radiotherapy need to be reduced. Unnecessary exposure to imaging studies that use ionizing radiation (plain radiograph, CT scan) should be avoided and use of MRI and/or ultrasound considered. Live vaccines (e.g., live vaccines for tuberculosis, measles, mumps, rubella, and varicella) should not be given.

Evaluation of relatives at risk: It is appropriate to offer molecular genetic testing for the familial NBN pathogenic variants to apparently asymptomatic adult relatives of an affected individual in order to identify family members who are heterozygous for an NBN pathogenic variant and would benefit from monitoring for malignancy.

Genetic counseling.

NBS is inherited in an autosomal recessive manner. At conception, each sib of an affected individual has a 25% chance of inheriting both pathogenic variants and being affected, a 50% chance of inheriting one pathogenic variant and being a heterozygote, and a 25% chance of inheriting neither of the familial NBN pathogenic variants. Heterozygotes are not at risk for NBS. However, heterozygous NBN pathogenic variants may be associated with an increased risk for breast cancer in women and prostate cancer in men. Carrier testing for at-risk family members and prenatal and preimplantation genetic testing are possible if the pathogenic variants in the family are known.

Suggestive Findings

Nijmegen breakage syndrome (NBS) should be suspected in individuals with the following clinical and supportive laboratory findings.

Clinical features

• Disproportionate microcephaly that is progressive
• Craniofacial features that include a sloping forehead, upward-slanted palpebral fissures, prominent nose, relatively large ears, and retrognathia
• Growth deficiency that is more pronounced from birth until age two years, with mild improvement thereafter
• Recurrent infections including pneumonia, bronchitis, sinusitis, otitis media, and mastoiditis
• Malignancies, predominantly of lymphoid origin
• Decline in intellectual ability, from normal or borderline-normal during early childhood to moderate intellectual disability in older individuals

Supportive laboratory findings

• Immunodeficiency involving the humoral and cellular systems [Wolska-Kuśnierz et al 2015]:
  • The most frequent deficit was of IgG found in 62% of affected individuals and IgA deficiency in 57%.
  • Deficiencies of IgG subclasses are frequent even when the IgG serum concentration is normal (IgG4, IgG2, and IgG3, in decreasing order).
  • The most commonly reported defects in cellular immunity include reduced absolute numbers of total B cells (CD19+/CD20+), CD3+ T cells, and CD4+ T cells; these are observed in 80%-89% of affected individuals.
  • The in vitro proliferation of T and B lymphocytes to antigen and/or mitogenic stimuli is moderately or severely reduced in majority of affected individuals, compared to age-matched healthy controls.
• Chromosome instability
  • Inversions and translocations involving chromosomes 7 and 14 are observed in PHA-stimulated lymphocytes in 10%-50% of metaphases.
  • The breakpoints most commonly involved are 7p13, 7q35, 14q11, and 14q32, which are the loci for immunoglobulin and T-cell receptor genes.
• Radiation sensitivity. Cells from individuals with NBS have a decrease in colony-forming ability following exposure to ionizing radiation and radiomimetics in vitro.
  Note: This test requires that a lymphoblastoid cell line be established. Because the process is more commonly performed in a research lab than in a clinical lab, the test may not be widely available clinically.

Establishing the Diagnosis

The diagnosis of NBS is established in a proband with suggestive findings and biallelic pathogenic (or likely pathogenic) variants in NBN identified by molecular genetic testing (see Table 1) and/or absent nibrin protein on an immunoblotting assay.

Note: Per ACMG/AMP variant interpretation guidelines, the terms "pathogenic variant" and "likely pathogenic variant" are synonymous in a clinical setting, meaning that both are considered diagnostic and can be used for clinical decision making [Richards et al 2015]. Reference to "pathogenic variants" in this GeneReview is understood to include any likely pathogenic variants.

Clinical Description

Nijmegen breakage syndrome (NBS) is characterized by progressive microcephaly, growth deficiency that improves with age, recurrent sinopulmonary infections, an increased risk for lymphoma, and premature ovarian failure in females. Developmental milestones are attained at the usual time during the first year; however, borderline delays in development and hyperactivity may be observed in early childhood. Intellectual abilities tend to decline over time. Secondary malignancies including solid tumors have been reported in several individuals.

Growth. Children with NBS are generally born with weight below normal for gestational age and microcephaly (i.e., head circumference >2 SD below the mean for age and sex). Microcephaly progresses with age – in contrast to linear growth, which may improve with age, causing disproportionate head dimensions compared to the rest of the body. Microcephaly is occasionally masked by hydrocephaly or developmental abnormalities of the brain [Szczałuba et al 2012].

Growth deficiency in the first years of life results in length/height that is usually below the third centile by age two years. Thereafter, linear growth velocity tends to normalize; however, many individuals remain shorter than their peers (i.e., affected individuals do not experience catch-up growth). Some adults, both females and males, can achieve height within lower-normal ranges [Chrzanowska et al 2012].

Craniofacial features. The craniofacial features discussed in Suggestive Findings are found in the majority of affected individuals and become more pronounced with age as microcephaly progresses.

Infections. Respiratory infections are the most common; recurrent pneumonia and bronchitis may result in bronchiectasis, and even in pulmonary failure and early death. Chronic diarrhea and urinary tract infections may also occur. The spectrum and frequency of infections and autoimmune complications in a large group of individuals with NBS was reported by Wolska-Kuśnierz et al [2015]. Correlation of the severity of respiratory tract infections with some humoral and cellular immune parameters was also presented. Most respiratory tract infections were caused by community-acquired pathogens; only about 5% of individuals suffered from opportunistic infections [Wolska-Kuśnierz et al 2015]. Another study showed low frequency of protective IgG antibodies to HBsAg after vaccination with Engerix-B^®, indicating a very weak specific response [Gregorek et al 2002].

Buchbinder et al [2019] reported the presence of rubella-positive cutaneous and visceral granulomas following rubella vaccination in individuals with NBS. One individual with NBS had pulmonary granulomas with no evidence of an infectious pathogen or any manifestations of systemic granulomatosis of lymphoid malignancy [Marczak et al 2018].

Malignancy. According to Chrzanowska et al [2012], 40% of affected individuals reported to date have developed malignancies before age 20 years. Malignancies are primarily lymphomas [Gładkowska-Dura et al 2008, Wolska-Kuśnierz et al 2015]. Approximately 45% of lymphomas are of B-cell origin and 55% are T-cell lymphomas. Although complete clinical remission (for >5 years) can be successfully achieved, in a proportion of affected individuals outcome is complicated by relapse or the development of a second malignancy [Dembowska-Baginska et al 2009, Bienemann et al 2011].

Several children have developed solid tumors, including medulloblastomas, glioma, rhabdomyosarcomas, and bilateral ovarian germ cell tumor (in a female) [Chrzanowska et al 1997, Hiel et al 2001, Bakhshi et al 2003, Distel et al 2003, Meyer et al 2004, Sharapova et al 2021, Krawczyk et al 2022]. Radiotherapy of central nervous system tumors (medulloblastoma) caused severe complications and death in three individuals with NBS [Chrzanowska et al 1997, Bakhshi et al 2003, Distel et al 2003].

A recent study of 241 individuals with NBS showed improved long-term survival in those treated with hematopoietic stem cell transplantation (HSCT) during first malignancy remission [Wolska-Kusnierz et al 2021]. In a second study of 136 individuals with NBS – 62 of whom developed malignancies – seven individuals were treated with HSCT due to leukemia/lymphoma; six, who were cancer-free, were transplanted due to immunodeficiency [Sharapova et al 2021].

Psychomotor and intellectual development. Developmental milestones are attained at the usual time during the first year. Normal or borderline intellectual development and psychomotor hyperactivity may be observed in early childhood / preschool age. Intellectual abilities tend to decline, with mild-to-moderate intellectual disability during childhood. Affected children are described as having a cheerful, shy personality with good interpersonal skills.

Fertility. Results of a longitudinal study demonstrated the presence of hypergonadotropic hypogonadism in a large cohort of affected females, all of whom were homozygous for the common c.657_661del5 pathogenic variant [Chrzanowska et al 2010a].

No detailed studies of fertility in males with NBS have been published; however, puberty initiation and progress are comparable to healthy boys [Chrzanowska et al 2010b]. Warcoin et al [2009] described two adult sibs, a male with oligo-terato-asthenozoospermia and a female with premature ovarian failure, who had biallelic truncating variants in NBN but none of the other clinical features of NBS.

Other findings

• Irregular skin pigmentation in the form of irregular hyperpigmented or hypopigmented macules is seen in most affected individuals. In some affected individuals, progressive sarcoid-like granulomas are observed [Yoo et al 2008, Pasic et al 2012].
• Congenital malformations, usually observed in single cases, include anomalies of the central nervous system (e.g., hydrocephaly, schizencephaly, arachnoid cysts), choanal atresia, cleft lip and palate, tracheal hypoplasia, preaxial or postaxial polydactyly, horseshoe kidney, hydronephrosis, hypospadias, anal stenosis/atresia, and congenital hip dysplasia.

Genotype-Phenotype Correlations

The common pathogenic variant c.657_661del5 and most other loss-of-function variants result in typical features of NBS. However, exceptions have been reported. There are two reports of families in which biallelic truncating variants in NBN occur in individuals with milder features:

• Varon et al [2006] described a woman age 53 years with NBS who was homozygous for the NBN truncating allele c.741_742dupGG. She had a somewhat milder phenotype, including microcephaly, chromosome instability, immunodeficiency, and primary amenorrhea. (Her sister, with similar clinical manifestations, had died at age 20 years of malignant lymphoma [Maraschio et al 1986]). However, analysis of transcripts from the woman's cells indicated a highly prevalent alternatively spliced form of NBN lacking exons 6 and 7 (where the pathogenic variant is located). This transcript codes for a 73-kd form of NBN with an internal deletion.
• Warcoin et al [2009] described a family in which two healthy adult sibs, a sister and brother, had biallelic truncating variants in NBN (p.Tyr110Ter and p.Trp375Ter). Neither sib had short stature, reduced head circumference, or dysmorphic facial features; however, both were referred for fertility defects (premature ovarian failure and oligo-terato-asthenozoospermia) and were subsequently found to have the cellular phenotypes typical of NBS, including chromosome instability, hypersensitivity to ionizing radiation, and impaired checkpoint responses.

Nomenclature

The Nijmegen breakage syndrome (NBS) was described by Weemaes et al [1981].

Three Czech families with Seemanová syndrome [Seemanová et al 1985] were later identified as having NBS.

Prevalence

No reliable estimates of worldwide prevalence exist, but it is likely to approximate 1:100,000 live births.

NBS is most common in Eastern European / Slavic populations. Studies in Poland, the Czech Republic, and Ukraine have suggested that the carrier frequency of the common allele approaches 1:155 in these populations [Varon et al 2000, Seemanová et al 2004]. The highest reported prevalence is in the Sorbian population, an isolated Slavic group from southeastern Germany, in whom the carrier frequency is estimated at 1:34 [Maurer et al 2010]. In a cohort of 136 individuals with NBS from Belarus, Ukraine, Russia, and Latvia, the highest prevalence was found in Belarus and Ukraine (2.3 and 1.3 in 1 million, respectively), with the highest incidence in western Belarus and western Ukraine (>2:100,000) [Sharapova et al 2021].

Evaluations Following Initial Diagnosis

To establish the extent of disease and needs in an individual diagnosed with NBS, the evaluations summarized in Table 4 (if not performed as part of the evaluation that led to the diagnosis) are recommended.

Treatment of Manifestations

Surveillance

Carriers (heterozygotes)

• Parents. As obligate carriers, parents should be monitored for malignancy, in particular breast cancer in women and prostate cancer in men. No consensus tumor screening protocols for carriers have been published.
• At-risk sibs. Evidence of cancer risk in young carriers is insufficient to warrant screening in childhood.

Agents/Circumstances to Avoid

Because the cells from individuals with NBS are as radiosensitive in vitro as those from individuals with ataxia-telangiectasia (another chromosome instability syndrome), conventional doses of radiation used in radiotherapy could be lethal in individuals with NBS. Family members should be made aware of the risk associated with radiotherapy so that they can discuss appropriate treatment options if a malignancy is diagnosed.

Similarly, unnecessary exposure to ionizing radiation should be avoided; instead of radiograph or CT scan, MRI and/or ultrasound examination are strongly recommended.

Live vaccines (e.g., live vaccines for tuberculosis, measles, mumps, rubella, and varicella) should not be given.

Evaluation of Relatives at Risk

It is appropriate to offer molecular genetic testing for the NBN pathogenic variants identified in the proband to apparently asymptomatic adult relatives of an affected individual in order to identify family members who are heterozygous for an NBN pathogenic variant and would benefit from monitoring for malignancy (see Clinical Description, Heterozygotes and Surveillance, Carriers).

See Genetic Counseling for issues related to testing of at-risk relatives for genetic counseling purposes.

Therapies Under Investigation

Search ClinicalTrials.gov in the US and EU Clinical Trials Register in Europe for access to information on clinical studies for a wide range of diseases and conditions. Note: There may not be clinical trials for this disorder.

Mode of Inheritance

Nijmegen breakage syndrome (NBS) is inherited in an autosomal recessive manner.

Risk to Family Members

Parents of a proband

• The parents of an affected child are presumed to be heterozygous for an NBN pathogenic variant.
• Molecular genetic testing is recommended for the parents of a proband to confirm that both parents are heterozygous for an NBN pathogenic variant and to allow reliable recurrence risk assessment. If a pathogenic variant is detected in only one parent and parental identity testing has confirmed biological maternity and paternity, the following possibilities should be considered:
  • One of the pathogenic variants identified in the proband occurred as a de novo event in the proband or as a postzygotic de novo event in a mosaic parent [Jónsson et al 2017].
  • Uniparental isodisomy for the parental chromosome with the pathogenic variant resulted in homozygosity for the pathogenic variant in the proband.
• Heterozygotes are not at risk for NBS; however, in some populations, there is clear evidence of increased cancer risk among individuals heterozygous for an NBN pathogenic variant (e.g., c.657_661del5) (see Clinical Description, Heterozygotes). Heterozygous parents should be monitored for malignancy, particularly breast cancer in women and prostate cancer in men (see Surveillance).

Sibs of a proband

• If both parents are known to be heterozygous for an NBN pathogenic variant, each sib of an affected individual has at conception a 25% chance of inheriting biallelic pathogenic variants and having NBS, a 50% chance of inheriting one pathogenic variant and being heterozygous, and a 25% chance of inheriting neither of the familial NBN pathogenic variants.
• Heterozygotes are not at risk for NBS; however, in some populations there is clear evidence of increased cancer risk among individuals heterozygous for an NBN pathogenic variant (e.g., c.657_661del5) (see Clinical Description, Heterozygotes). Adult heterozygous sibs should be monitored for malignancy, particularly breast cancer in women and prostate cancer in men (see Surveillance).

Offspring of a proband. To date, individuals with NBS are not known to reproduce.

Other family members. Each sib of the proband's parents is at a 50% risk of being heterozygous for an NBN pathogenic variant and at increased risk for malignancy (see Clinical Description, Heterozygotes).

Heterozygote Detection

Heterozygote testing for at-risk relatives requires prior identification of the NBN pathogenic variants in the family.

Related Genetic Counseling Issues

See Management, Evaluation of Relatives at Risk for information on evaluating at-risk relatives for the purpose of early diagnosis and treatment.

Family planning

• The optimal time for determination of genetic risk and discussion of the availability of prenatal/preimplantation genetic testing is before pregnancy.
• It is appropriate to offer genetic counseling (including discussion of potential risks to offspring and reproductive options) to young adults who are heterozygotes or are at risk of being heterozygotes.

Prenatal Testing and Preimplantation Genetic Testing

Once the NBN pathogenic variants have been identified in an affected family member, prenatal and preimplantation genetic testing for NBS are possible.

Differences in perspective may exist among medical professionals and within families regarding the use of prenatal testing. While most centers would consider use of prenatal testing to be a personal decision, discussion of these issues may be helpful.

Molecular Pathogenesis

NBN encodes nibrin, also known as p95. Nibrin is ubiquitously expressed. There is no sequence homology between nibrin and other known proteins. However, nibrin contains a forkhead-associated domain and two breast cancer carboxy-terminal domains, which are involved in cellular responses to DNA damage. In normal fibroblasts, nibrin is associated with two other proteins involved in DNA repair, hMre11 and hRad50. On exposure to ionizing radiation, the associated proteins hMre11, hRad50, and nibrin form nuclear foci at sites where DNA repair has taken place. Nibrin targets the NBN/Mre11/Rad50 complex to sites of double-strand breaks and interacts with ATM kinase to coordinate cell cycle arrest with DNA repair [Carney et al 1998, Matsuura et al 2004, Falck et al 2005].

Most known NBN pathogenic variants are predicted to result in truncation of the nibrin protein. All known NBS-related pathogenic variants occur in exons 6-10; presumably reflecting a requirement for production of a C-terminal protein fragment of nibrin that occurs by translational reinitiation mechanism [Maser et al 2001]. The requirement that protein termination and reinitiation occur in the same reading frame potentially limits the pathogenic variants that can give rise to NBS.

Mechanism of disease causation. Loss of function

Author History

Krystyna H Chrzanowska, MD, PhD (2017-present)
Patrick Concannon, PhD; University of Florida Genetics Institute (1999-2014)
Ilja Demuth, PhD (2014-present)
Martin Digweed, PhD; Universitätsmedizin Berlin (2014-2017)
Richard Gatti, MD; University of California Los Angeles (1999-2014)
Raymonda Varon, PhD (2014-present)

Revision History

• 30 November 2023 (sw/aa) Revision: added information about cancer surveillance for heterozygotes in Evaluation of Relatives at Risk; deleted ATM from Differential Diagnosis
• 18 August 2022 (sw) Comprehensive update posted live
• 2 February 2017 (ma) Comprehensive update posted live
• 8 May 2014 (me) Comprehensive update posted live
• 1 March 2011 (me) Comprehensive update posted live
• 14 June 2005 (me) Comprehensive update posted live
• 14 March 2003 (me) Comprehensive update posted live
• 17 May 1999 (me) Review posted live
• 5 January 1999 (pc) Original submission

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