Mosaic Neurofibromatosis Type 1 in Children: A Single-Institution Experience

Mosaicism in Tumor Suppressor Gene Syndromes: Prevalence, Diagnostic Strategies, and Transmission Risk

A mosaic state arises when pathogenic variants are acquired in certain cell lineages during postzygotic development, and mosaic individuals may present with a generalized or localized phenotype. Here, we review the current state of knowledge regarding mosaicism for eight common tumor suppressor genes-NF1, NF2, TSC1, TSC2, PTEN, VHL, RB1, and TP53-and their related genetic syndromes/entities. We compare and discuss approaches for comprehensive diagnostic genetic testing, the spectrum of variant allele frequency, and disease severity. We also review affected individuals who have no mutation identified after conventional genetic analysis, as well as genotype-phenotype correlations and transmission risk for each tumor suppressor gene in full heterozygous and mosaic patients. This review provides new insight into similarities as well as marked differences regarding the appreciation of mosaicism in these tumor suppressor syndromes.

Challenges in the diagnosis of neurofibromatosis type 1 (NF1) in young children facilitated by means of revised diagnostic criteria including genetic testing for pathogenic NF1 gene variants

Neurofibromatosis type 1 (NF1) is the most frequent disorder associated with multiple café-au-lait macules (CALM) which may either be present at birth or appear during the first year of life. Other NF1-associated features such as skin-fold freckling and Lisch nodules occur later during childhood whereas dermal neurofibromas are rare in young children and usually only arise during early adulthood. The NIH clinical diagnostic criteria for NF1, established in 1988, include the most common NF1-associated features. Since many of these features are age-dependent, arriving at a definitive diagnosis of NF1 by employing these criteria may not be possible in infancy if CALM are the only clinical feature evident. Indeed, approximately 46% of patients who are diagnosed with NF1 later in life do not meet the NIH diagnostic criteria by the age of 1 year. Further, the 1988 diagnostic criteria for NF1 are not specific enough to distinguish NF1 from other related disorders such as Legius syndrome. In this review, we outline the challenges faced in diagnosing NF1 in young children, and evaluate the utility of the recently revised (2021) diagnostic criteria for NF1, which include the presence of pathogenic variants in the NF1 gene and choroidal anomalies, for achieving an early and accurate diagnosis.

Clinical features and disease severity in patients with mosaic neurofibromatosis type 1: a single-center study and literature review

Background

The mosaic form of neurofibromatosis type 1 (NF1) is called mosaic NF1 (MNF1). No specific MNF1 follow-up guidelines exist. It is debatable if patients with MNF1 should be clinically examined and undergo follow-up in accordance with the standard NF1 guidelines, as MNF1 patients more often may develop more benign phenotypes and thereby less disease-associated complications including cognitive impairment. We discussed the need for a specific MNF1 follow-up guideline with focus on frequency of plexiform neurofibromas and NF1-associated complications.

Method

A systematic retrospective data collection in a MNF1 cohort from one of two Danish national centers of NF1 Expertise was completed. Data collected included demographics, clinical features including NF1 diagnostic criteria and NF1-associated complications. Recent literature in the field was reviewed.

Results

We identified 17 patients with MNF1 with a median age of 37 years [4; 66]. Eleven (65%) were females. Five patients (30%) had a plexiform neurofibroma. The median age at detection of plexiform neurofibroma was 30 years [14; 60]. Nine (53%) had at least one NF1-related complication; scoliosis, hypertension, ADHD, learning disability, language delay, autism and delay in gross and fine motor function development. We reviewed nine articles. In total, 126 cases were described within three case-series. Nineteen (15%) had a plexiform neurofibroma and in total, 23 NF1-associated complications were reported including language delay, learning disability and skeletal abnormalities. Furthermore, from the literature it was evident that the diagnosing of MNF1 varies among physicians and across countries.

Conclusion

Patients with MNF1 present with plexiform neurofibromas and other NF1-related complications with a frequency requiring that follow-up of MNF1 patients should be in accordance with the standard NF1 guideline in both childhood and adulthood. Physicians should be aware of cognitive impairment as a complication to MNF1. To develop a specific MNF1 follow-up guideline, there is a need for an international consensus on the diagnostic criteria for MNF1 and a follow-up study conducted in a larger MNF1 cohort.

The Clinical Spectrum of Mosaic Neurofibromatosis in Children and Adolescents

BACKGROUND

Segmental neurofibromatosis was initially described by Miller and Sparks (1977) as manifestations of neurofibromatosis limited to a dermatomal, localized distribution. Now termed mosaic neurofibromatosis, previous literature described this disease in children and adolescents with individual case reports and small-numbered case series. This study presents a large series of children and adolescents with mosaic neurofibromatosis.

METHODS

A retrospective chart review of a single institution medical record database was performed on all cases of mosaic neurofibromatosis diagnosed between the years 1998 and 2017. Eligible subjects were determined by 2 criteria: (1) segmental or unilateral expression of one of more signs of NF I according to those outlined in the NIH criteria and (2) were under 18 years of age at the time of diagnosis. Select information extracted include location of clinical features, NF manifestations (neurofibromas, plexiform neurofibromas, café-au-lait spots, freckling, Lisch nodules), presence of a diffuse area of cutaneous hyperpigmentation, and other significant medical conditions.

RESULTS

Sixty-eight cases met established criteria. Average age at diagnosis was 8.28 ± 4.47 years. Thirty-seven (54%) were male and 31 (46%) were female. Localization of the dermatologic manifestations is as follows: left side in 28 (41%) cases, right side in 32 (47%) cases, and bilateral in 8 (11%) cases. Café-au-lait lesions appeared in 64 (94%) of cases and 14 (21%) had axillary and inguinal freckling.

CONCLUSIONS

This study expands our understanding of the disease characteristics seen in children and adolescents with mosaic neurofibromatosis and confirms the need to focus on pigmentary changes in children with mosaic neurofibromatosis.