A new nonsense mutation in the NF1 gene with neurofibromatosis-Noonan syndrome phenotype

The gene diagnosis of neurofibromatosis type I with headache as the main symptom: A case report and review of the literature

Neurofibromatosis type I (NF1) is an autosomal dominant disease. Some NF1 patients experience atypical clinical manifestations, genetic testing is not widely available, and the types of mutations vary; thus, they are prone to misdiagnosis and missed diagnosis. Although headache is not included in the diagnostic criteria for NF1, the incidence of headache in NF1 patients is not low. We report an NF1 family in which the proband presented with prominent headache and atypical clinical presentation, with limited skin pigmentation. We identified a frameshift mutation (c.1541_1542del, p. Q514Rfs*) in the NF1 gene by whole-exome sequencing of this family, and the patients were diagnosed with NF1. We hope to attract the attention of clinicians to these patients and improve genetic testing as soon as possible to increase the diagnosis rate.

Chinese patient with neurofibromatosis-Noonan syndrome caused by novel heterozygous NF1 exons 1-58 deletion: a case report

BACKGROUND

Neurofibromatosis-Noonan syndrome (NFNS) is a rare autosomal dominant hereditary disease. We present a case of NFNS due to the heterozygous deletion of exons 1-58 of the NF1 gene on chromosome 17 in a 15-month-old boy.

CASE PRESENTATION

A 15-month-old boy was admitted for motor and language developmental delay, numerous café-au-lait spots, hypertelorism, left blepharoptosis, pectus excavatum, cryptorchidism, secondary atrial septal defect, and UBOs (undefined bright objects) revealed by cranial MRI T2FLAIR in basal ganglia and cerebellum. Using whole exome sequencing, we identified a de novo heterozygous deletion including exons 1-58 of the NF1 gene.

CONCLUSION

Although genetic tests are useful tools for diagnosis of NFNS, NF1, or NS, comprehensive analysis of genetic factors and phenotypes is indispensable in the clinical practice. To the best of our knowledge, this case presents the first Chinese NFNS case due to NF1 defects, and the NF1 exons 1-58 deletion-related phenotype is unlike any other reported case.

Novel association of neurofibromatosis type 1-causing mutations in families with neurofibromatosis-Noonan syndrome

Neurofibromatosis-Noonan syndrome (NFNS) is a rare condition with clinical features of both neurofibromatosis type 1 (NF1) and Noonan syndrome (NS). All three syndromes belong to the RASopathies, which are caused by dysregulation of the RAS-MAPK pathway. The major gene involved in NFNS is NF1, but co-occurring NF1 and PTPN11 mutations in NFNS have been reported. Knowledge about possible involvement of additional RASopathy-associated genes in NFNS is, however, very limited. We present a comprehensive clinical and molecular analysis of eight affected individuals from three unrelated families displaying features of NF1 and NFNS. The genetic etiology of the clinical phenotypes was investigated by mutation analysis, including NF1, PTPN11, SOS1, KRAS, NRAS, BRAF, RAF1, SHOC2, SPRED1, MAP2K1, MAP2K2, and CBL. All three families harbored a heterozygous NF1 variant, where the first family had a missense variant, c.5425C>T;p.R1809C, the second family a recurrent 4bp-deletion, c.6789_6792delTTAC;p.Y2264Tfs*6, and the third family a splice-site variant, c.2991-1G>A, resulting in skipping of exon 18 and an in-frame deletion of 41 amino acids. These NF1 variants have all previously been reported in NF1 patients. Surprisingly, both c.6789_6792delTTAC and c.2991-1G>A are frequently associated with NF1, but association to NFNS has, to our knowledge, not previously been reported. Our results support the notion that NFNS represents a variant of NF1, genetically distinct from NS, and is caused by mutations in NF1, some of which also cause classical NF1. Due to phenotypic overlap between NFNS and NS, we propose screening for NF1 mutations in NS patients, preferentially when café-au-lait spots are present.