Molecular genetic testing for Neurofibromatosis type 1 (NF1).

LM Messiaen, PhD, T Callens, N Goderis, G Mortier, MD, PhD, F Speleman, PhD, A De Paepe, MD, PhD

Dpt. Medical Genetics, Ghent University Hospital, Belgium

AIM NF1 patients show neurofibromas, pigmentation anomalies and a variety of complications, including an increased risk for malignant peripheral nerve sheath tumors, optic gliomas and leukemias. We wanted to develop a sensitive and efficient mutation analysis for NF1, being one of the most common autosomal dominant disorders with 50% of patients being de novo cases. METHODS We developed a multi-tiered approach including: 1) protein truncation test (PTT) followed by sequencing of the region of interest; 2) FISH to detect total gene deletions; 3) sequencing of the complete cDNA to detect missense mutations; 4) Southern blot and cytogenetic analysis. RESULTS Using this cascade of techniques we identified 191 mutations in 200 unrelated NF1 patients. About 70% of the patients included were sporadic cases. The mutational spectrum is very complex. By PTT alone, 161 mutations were identified, one of them showing somatic mosaicism for a nonsense mutation. 30% of mutations are splicing errors, mostly outside the AG/GT 3’ and 5’ splice sites. 19 missense or small in-frame deletions, 4 total gene deletions and 1 translocation t(14;17)(q32;q11.2) were found. Most families carry a "private" mutation, but a limited number of recurrent mutations exist. Using this sensitive approach, we started to study the molecular basis of segmental NF and other clinical subtypes. CONCLUSIONS This approach is very sensitive and efficient and allows help with the diagnosis in sporadic patients or in young patients with NF1-related symptoms but not yet fulfilling the N.I.H. diagnostic criteria. It also provides the means to prepare for prenatal/pre implantation diagnosis, especially in sporadic patients.

KEY WORDS: mutation, segmental NF, prenatal.

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Paper presented at the International Symposium on Predictive Oncology and Intervention Strategies; Paris, France; February 9 - 12, 2002; in the section on Familial and Hereditary Cancer.