Growth in neurofibromatosis 1 microdeletion patients

Identification of an NF1 Microdeletion with Optical Genome Mapping

Neurofibromatosis type 1 (NF1) is a clinically heterogeneous neurocutaneous disorder inherited in autosomal dominant manner. Approximately 5-10% of the cases are caused by NF1 microdeletions involving the NF1 gene and its flanking regions. Microdeletions, which lead to more severe clinical manifestations, can be subclassified into four different types (type 1, 2, 3 and atypical) according to their size, the genomic location of the breakpoints and the number of genes included within the deletion. Besides the prominent hallmarks of NF1, patients with NF1 microdeletions frequently exhibit specific additional clinical manifestations like dysmorphic facial features, macrocephaly, overgrowth, global developmental delay, cognitive disability and an increased risk of malignancies. It is important to identify the genes co-deleted with NF1, because they are likely to have an effect on the clinical manifestation. Multiplex ligation-dependent probe amplification (MLPA) and microarray analysis are the primary techniques for the investigation of NF1 microdeletions. However, based on previous research, optical genome mapping (OGM) could also serve as an alternative method to identify copy number variations (CNVs). Here, we present a case with NF1 microdeletion identified by means of OGM and demonstrate that this novel technology is a suitable tool for the identification and classification of the NF1 microdeletions.

Imagawa-Matsumoto syndrome: SUZ12-related overgrowth disorder

The SUZ12 gene encodes a subunit of polycomb repressive complex 2 (PRC2) that is essential for development by silencing the expression of multiple genes. Germline heterozygous variants in SUZ12 have been found in Imagawa-Matsumoto syndrome (IMMAS) characterized by overgrowth and multiple dysmorphic features. Similarly, both EZH2 and EED also encode a subunit of PRC2 each and their pathogenic variants cause Weaver syndrome and Cohen-Gibson syndrome, respectively. Clinical manifestations of these syndromes significantly overlap, although their different prevalence rates have recently been noted: generalized overgrowth, intellectual disability, scoliosis, and excessive loose skin appear to be less prevalent in IMMAS than in the other two syndromes. We could not determine any apparent genotype-phenotype correlation in IMMAS. The phenotype of neurofibromatosis type 1 arising from NF1 deletion was also shown to be modified by the deletion of SUZ12, 560 kb away. This review deepens our understanding of the clinical and genetic characteristics of IMMAS together with other overgrowth syndromes related to PRC2. We also report on a novel IMMAS patient carrying a splicing variant (c.1023+1G>C) in SUZ12. This patient had a milder phenotype than other previously reported IMMAS cases, with no macrocephaly or overgrowth phenotypes, highlighting the clinical variation in IMMAS.

Head circumference and anthropometric changes and their relation to plexiform and skin neurofibromas in sporadic and familial neurofibromatosis 1 Brazilian adults: a cross-sectional study

BACKGROUND

Neurofibromatosis 1 (NF1) is a common autosomal dominant syndrome with complete penetrance and highly variable expressivity. The cutaneous neurofibroma (Cnf) and plexiform neurofibroma (Pnf), café-au-lait spots, and freckle-like lesions are common in NF1, but many other manifestations can occur. We aimed to evaluate head circumference, height, weight, body mass index (BMI), head circumference-to-height ratio (HCHR) and waist-hip ratio (WHR) in adult NF1 Brazilian individuals versus a paired control group and investigate their correlation with the presence of clinically visible Pnfs, and number of "skin neurofibromas" (Snf), which include both cutaneous and subcutaneous neurofibromas.

METHODS

A case-control study was conducted with 168 individuals, 84 with NF1 and 84 without NF1, paired by sex and age. Head circumference and anthropometric measurements, Snf quantification, evaluation of clinically visible Pnf and familial inheritance were accessed.

RESULTS

Prevalence of macrocephaly was significantly higher in NF1 women. Height and weight were significantly lower in both males and females with NF1. HCHR was higher in the NF1 group than in the control group for both sexes. BMI was significantly lower in men with NF1. Waist and hip circumferences were significantly reduced in NF compared with the controls, but the mean WHR was significantly lower only in NF1 women. No correlation was found between the Snf and head circumference and anthropometric measurements, sex or family history. The presence and larger size of clinically visible plexiform neurofibromas were associated with normal stature (p = 0.037 and p = 0.003, respectively).

CONCLUSIONS

NF1 individuals have increased prevalence of macrocephaly, short stature, low BMI, and reduced abdominal fat. There is no relation between head circumference and anthropometric data with family history, or neurofibromas.

Atypical NF1 Microdeletions: Challenges and Opportunities for Genotype/Phenotype Correlations in Patients with Large NF1 Deletions

Patients with neurofibromatosis type 1 (NF1) and type 1 NF1 deletions often exhibit more severe clinical manifestations than patients with intragenic NF1 gene mutations, including facial dysmorphic features, overgrowth, severe global developmental delay, severe autistic symptoms and considerably reduced cognitive abilities, all of which are detectable from a very young age. Type 1 NF1 deletions encompass 1.4 Mb and are associated with the loss of 14 protein-coding genes, including NF1 and SUZ12. Atypical NF1 deletions, which do not encompass all 14 protein-coding genes located within the type 1 NF1 deletion region, have the potential to contribute to the delineation of the genotype/phenotype relationship in patients with NF1 microdeletions. Here, we review all atypical NF1 deletions reported to date as well as the clinical phenotype observed in the patients concerned. We compare these findings with those of a newly identified atypical NF1 deletion of 698 kb which, in addition to the NF1 gene, includes five genes located centromeric to NF1. The atypical NF1 deletion in this patient does not include the SUZ12 gene but does encompass CRLF3. Comparative analysis of such atypical NF1 deletions suggests that SUZ12 hemizygosity is likely to contribute significantly to the reduced cognitive abilities, severe global developmental delay and facial dysmorphisms observed in patients with type 1 NF1 deletions.

Impacts of NF1 Gene Mutations and Genetic Modifiers in Neurofibromatosis Type 1

Neurofibromatosis type 1 (NF1) is a tumor predisposition genetic disorder that directly affects more than 1 in 3,000 individuals worldwide. It results from mutations of the NF1 gene and shows almost complete penetrance. NF1 patients show high phenotypic variabilities, including cafe-au-lait macules, freckling, or other neoplastic or non-neoplastic features. Understanding the underlying mechanisms of the diversities of clinical symptoms might contribute to the development of personalized healthcare for NF1 patients. Currently, studies have shown that the different types of mutations in the NF1 gene might correlate with this phenomenon. In addition, genetic modifiers are responsible for the different clinical features. In this review, we summarize different genetic mutations of the NF1 gene and related genetic modifiers. More importantly, we focus on the genotype–phenotype correlation. This review suggests a novel aspect to explain the underlying mechanisms of phenotypic heterogeneity of NF1 and provides suggestions for possible novel therapeutic targets to prevent or delay the onset and development of different manifestations of NF1.

Severe Phenotype in Patients with Large Deletions of NF1

Complete deletion of the NF1 gene is identified in 5-10% of patients with neurofibromatosis type 1 (NF1). Several studies have previously described particularly severe forms of the disease in NF1 patients with deletion of the NF1 locus, but comprehensive descriptions of large cohorts are still missing to fully characterize this contiguous gene syndrome. NF1-deleted patients were enrolled and phenotypically characterized with a standardized questionnaire between 2005 and 2020 from a large French NF1 cohort. Statistical analyses for main NF1-associated symptoms were performed versus an NF1 reference population. A deletion of the NF1 gene was detected in 4% (139/3479) of molecularly confirmed NF1 index cases. The median age of the group at clinical investigations was 21 years old. A comprehensive clinical assessment showed that 93% (116/126) of NF1-deleted patients fulfilled the NIH criteria for NF1. More than half had café-au-lait spots, skinfold freckling, Lisch nodules, neurofibromas, neurological abnormalities, and cognitive impairment or learning disabilities. Comparison with previously described "classic" NF1 cohorts showed a significantly higher proportion of symptomatic spinal neurofibromas, dysmorphism, learning disabilities, malignancies, and skeletal and cardiovascular abnormalities in the NF1-deleted group. We described the largest NF1-deleted cohort to date and clarified the more severe phenotype observed in these patients.

Evaluation of clinical findings and neurofibromatosis type 1 bright objects on brain magnetic resonance images of 60 Turkish patients with NF1 gene variants

Neurofibromatosis type 1 (NF1) is caused by mutations in the NF1 gene. This retrospective study aims to evaluate the clinical manifestations and brain magnetic resonance images (MRI) analysis in 60 genetically confirmed NF1 patients. The results of next-generation sequencing (NGS), Sanger sequencing, and MLPA of NF1 gene were evaluated. A total of 54 different variants were identified. Fourteen out of them were novel variants (25.9%). Patients who complied with NIH criteria had most frequently frameshift variants (11/32 patients), and those with only CALMs had missense variants (9/28 patients). Neurofibromatosis type 1 bright objects (NBOs) on T2-weighted MRI were detected in 42 patients (42/56; 75%). These brain lesions were detected mostly in basal ganglia and in cerebellar vermis. NBOs were detected more in the patients who complied with NIH criteria (80.6%) compared to those who were only CALMs (68%). While frameshift variants (33.3%) were the most common type variants in the patients who had NBOs, the most common variants were splicing (35.7%) and missense (35.7%) variants in the patients whose MRIs were normal. Frameshift variants (11/28 patients; 39.3%) were the most common in the patients with more than one brain locus involvement. Therefore, we consider that frameshift variants may be associated with increased incidence of NBOs and involvement of more than one brain locus. In addition, NBOs may occur less frequently in the patients with splicing variants. To our knowledge, this is the first study evaluated the relationship between NF1 gene variants and NBOs. Future studies may help us understand the etiology of NBOs.

Clinical characterization of children and adolescents with NF1 microdeletions

PURPOSE

An estimated 5-11% of patients with neurofibromatosis type 1 (NF1) harbour NF1 microdeletions encompassing the NF1 gene and its flanking regions. The purpose of this study was to evaluate the clinical phenotype in children and adolescents with NF1 microdeletions.

METHODS

We retrospectively analysed 30 children and adolescents with NF1 microdeletions pertaining to externally visible neurofibromas. The internal tumour load was determined by volumetry of whole-body magnetic resonance imaging (MRI) in 20 children and adolescents with NF1 microdeletions. Furthermore, the prevalence of global developmental delay, autism spectrum disorder and attention deficit hyperactivity disorder (ADHD) were evaluated.

RESULTS

Children and adolescents with NF1 microdeletions had significantly more often cutaneous, subcutaneous and externally visible plexiform neurofibromas than age-matched patients with intragenic NF1 mutations. Internal neurofibromas were detected in all 20 children and adolescents with NF1 microdeletions analysed by whole-body MRI. By contrast, only 17 (61%) of 28 age-matched NF1 patients without microdeletions had internal tumours. The total internal tumour load was significantly higher in NF1 microdeletion patients than in NF1 patients without microdeletions. Global developmental delay was observed in 28 (93%) of 30 children with NF1 microdeletions investigated. The mean full-scale intelligence quotient in our patient group was 77.7 which is significantly lower than that of patients with intragenic NF1 mutations. ADHD was diagnosed in 15 (88%) of 17 children and adolescents with NF1 microdeletion. Furthermore, 17 (71%) of the 24 patients investigated had T-scores ≥ 60 up to 75, indicative of mild to moderate autistic symptoms, which are consequently significantly more frequent in patients with NF1 microdeletions than in the general NF1 population. Also, the mean total T-score was significantly higher in patients with NF1 microdeletions than in the general NF1 population.

CONCLUSION

Our findings indicate that already at a very young age, NF1 microdeletions patients frequently exhibit a severe disease manifestation which requires specialized long-term clinical care.

Neurofibromatosis type 1 of the child increases birth weight

Neurofibromatosis type 1 (NF1) is associated with reduced adult height, but there are no cohort studies on birth size. This retrospective study includes a cohort of 1,410 persons with NF1 and a matched comparison cohort from the general population. Figures for birth size were retrieved from the administrative registers of Finland, and the data were converted to standard deviation scores (SDS), defined as standard deviation difference to the reference population. The birth weight among infants with NF1 was higher than among infants without the disorder (adjusted mean difference [95% confidence interval]: 0.53 SDS [0.19–0.87]), as was the head circumference at birth (0.58 SDS [0.26–0.90]). The birth length of the NF1 infants did not differ significantly from the comparison cohort. The birth weight in the group consisting of NF1 and non‐NF1 infants of NF1 mothers was lower than among infants of mothers in the comparison cohort (−0.28 SDS [−0.51 to −0.06]), as was the birth length (−0.22 SDS [−0.45 to 0.00]). In conclusion, the birth weight and head circumference of persons with NF1 are significantly higher than those of persons without the disorder. NF1 of the mother reduces birth weight and birth length of the infant.

Phenotypic expression of a spectrum of Neurofibromatosis Type 1 (NF1) mutations identified through NGS and MLPA

Neurofibromatosis Type 1 (NF1) is caused by mutations of the NF1 gene. The aim of this study was to identify the genetic causes underlying the disease, attempt possible phenotype/genotype correlations and add to the NF1 mutation spectrum. A screening protocol based on genomic DNA was established in 168 patients, encompassing sequencing of all coding exons and adjoining introns using a custom targeted next generation sequencing protocol and subsequent confirmation of findings with Sanger sequencing. MLPA was used to detect deletions/duplications and positive findings were confirmed by RNA analysis. All novel findings were evaluated according to ACMG Standards and guidelines for the interpretation of sequence variants with the aid of in-silico bioinformatic tools and family segregation analysis. A germline variant was identified in 145 patients (86%). In total 49 known and 70 novel variants in coding and non-coding regions were identified. Seven patients carried whole or partial gene deletions. NF1 patients, present with high phenotypic variability even in cases where the same germline disease causing variant has been identified. Our findings will contribute to a better knowledge of the genetic causes and the phenotypic expression related to the disease.

Possible modifier genes in the variation of neurofibromatosis type 1 clinical phenotypes

Neurofibromatosis type 1 (NF1) is the most common neurogenetic disorder worldwide, caused by mutations in the (NF1) gene. Although NF1 is a single-gene disorder with autosomal-dominant inheritance, its clinical expression is highly variable and unpredictable. NF1 patients have the highest known mutation rate among all human disorders, with no clear genotype-phenotype correlations. Therefore, variations in NF1 mutations may not correlate with the variations in clinical phenotype. Indeed, for the same mutation, some NF1 patients may develop severe clinical symptoms whereas others will develop a mild phenotype. Variations in the mutant NF1 allele itself cannot account for all of the disease variability, indicating a contribution of modifier genes, environmental factors, or their combination. Considering the gene structure and the interaction of neurofibromin protein with cellular components, there are many possible candidate modifier genes. This review aims to provide an overview of the potential modifier genes contributing to NF1 clinical variability.

Growth hormone excess in children with neurofibromatosis type-1 and optic glioma

In children with neurofibromatosis type 1 (NF1) and optic pathways glioma (OPG), growth hormone (GH) excess has been rarely reported and mainly associated to central precocious puberty. The aim of our study is to evaluate the prevalence of GH excess, the association with central precocious puberty, the relation with tumor site and the evolution over time in a large cohort of children with NF1 and OPG. Sixty-four NF1 children with OPG were evaluated. Patients with stature and/or height velocity >2 SD for age were studied for GH secretion. Seven out of 64 children (10.9%) with NF1 and optic pathways glioma showed GH excess, isolated in 5 cases and associated to central precocious puberty in 2. All the children with GH excess had a tumor involving the chiasma. Children with GH excess underwent medical treatment with lanreotide and a minimum clinical/biochemical follow up of 2 years is reported. The present study demonstrates that GH excess should be considered as a relative frequent endocrine manifestation in NF1 patients, similarly to central precocious puberty. Therefore, these patients should undergo frequent accurate auxologic evaluations. On the other hand, an increase in height velocity in children with NF1, even despite normal ophthalmological exams, can suggest the presence of OPG and therefore represents an indication to perform brain MRI.

Emerging genotype-phenotype relationships in patients with large NF1 deletions

The most frequent recurring mutations in neurofibromatosis type 1 (NF1) are large deletions encompassing the NF1 gene and its flanking regions (NF1 microdeletions). The majority of these deletions encompass 1.4-Mb and are associated with the loss of 14 protein-coding genes and four microRNA genes. Patients with germline type-1 NF1 microdeletions frequently exhibit dysmorphic facial features, overgrowth/tall-for-age stature, significant delay in cognitive development, large hands and feet, hyperflexibility of joints and muscular hypotonia. Such patients also display significantly more cardiovascular anomalies as compared with patients without large deletions and often exhibit increased numbers of subcutaneous, plexiform and spinal neurofibromas as compared with the general NF1 population. Further, an extremely high burden of internal neurofibromas, characterised by >3000 ml tumour volume, is encountered significantly, more frequently, in non-mosaic NF1 microdeletion patients than in NF1 patients lacking such deletions. NF1 microdeletion patients also have an increased risk of malignant peripheral nerve sheath tumours (MPNSTs); their lifetime MPNST risk is 16–26%, rather higher than that of NF1 patients with intragenic NF1 mutations (8–13%). NF1 microdeletion patients, therefore, represent a high-risk group for the development of MPNSTs, tumours which are very aggressive and difficult to treat. Co-deletion of the SUZ12 gene in addition to NF1 further increases the MPNST risk in NF1 microdeletion patients. Here, we summarise current knowledge about genotype–phenotype relationships in NF1 microdeletion patients and discuss the potential role of the genes located within the NF1 microdeletion interval whose haploinsufficiency may contribute to the more severe clinical phenotype.