Postzygotic mosaicism in basal cell naevus syndrome

Detection of PTCH1 Copy-Number Variants in Mosaic Basal Cell Nevus Syndrome

Basal cell nevus syndrome (BCNS) is an inherited disorder characterized mainly by the development of basal cell carcinomas (BCCs) at an early age. BCNS is caused by heterozygous small-nucleotide variants (SNVs) and copy-number variants (CNVs) in the Patched1 (PTCH1) gene. Genetic diagnosis may be complicated in mosaic BCNS patients, as accurate SNV and CNV analysis requires high-sensitivity methods due to possible low variant allele frequencies. We compared test outcomes for PTCH1 CNV detection using multiplex ligation-probe amplification (MLPA) and digital droplet PCR (ddPCR) with samples from a BCNS patient heterozygous for a PTCH1 CNV duplication and the patient's father, suspected to have a mosaic form of BCNS. ddPCR detected a significantly increased PTCH1 copy-number ratio in the index patient's blood, and the father's blood and tissues, indicating that the father was postzygotic mosaic and the index patient inherited the CNV from him. MLPA only detected the PTCH1 duplication in the index patient's blood and in hair and saliva from the mosaic father. Our data indicate that ddPCR more accurately detects CNVs, even in low-grade mosaic BCNS patients, which may be missed by MLPA. In general, quantitative ddPCR can be of added value in the genetic diagnosis of mosaic BCNS patients and in estimating the recurrence risk for offspring.

Mutations of PTCH1 gene in two pedigrees with bifid rib-basal cell nevus-jaw cyst syndrome

Two male patients with bifid rib-basal cell nevus-jaw cyst syndrome (BCNS) were admitted to Department of Stomatology, the First Affiliated Hospital of Bengbu Medical College due to radiological findings of multiple low density shadows in the jaw. Clinical and imaging findings showed thoracic malformation, calcification of the tentorium cerebellum and falx cerebrum as well as widening of the orbital distance. Whole exon high-throughput sequencing was performed in two patients and their family members. The heterozygous mutations of c.C2541C>A(p.Y847X) and c.C1501C>T(p.Q501X) in PTCH1 gene were detected in both patients. Diagnosis of BCNS was confirmed. The heterozygous mutations of PTCH1 gene locus were also found in the mothers of the two probands. Proband 1 showed clinical manifestations of low intelligence, and heterozygous mutations of c.C2141T(p.P714L) and c.G3343A(p.V1115I) were detected in FANCD2 gene. Proband 2 had normal intelligence and no FANCD2 mutation. The fenestration decompression and curettage of jaw cyst were performed in both patients. Regular follow-up showed good bone growth at the original lesion, and no recurrence has been observed so far.

Genetic profiling of basal cell carcinomas detects postzygotic mosaicism in basal cell naevus syndrome

Basal cell naevus syndrome (BCNS) is associated with germline mutations in the PTCH1 gene. Postzygotic mosaicism can also cause BCNS. Here we describe two patients, one with multiple basal cell carcinomas (BCCs) and one with clinical BCNS, who had no PTCH1 mutation in DNA extracted from blood. In both patients, we performed genetic analysis on different BCCs, revealing the presence of a shared PTCH1 mutation in all tumours. Our findings show that in patients with symptoms of BCNS and initial absence of a PTCH1 mutation in blood, genetic profiling of BCCs can detect postzygotic mosaicism. What's already known about this topic? Basal cell naevus syndrome (BCNS) is associated with germline mutations in the PTCH1 gene, but it can also be caused by low-grade postzygotic mosaicism in PTCH1. What does this study add? In patients suspected of having BCNS or patients with multiple basal cell carcinomas (BCCs) with a special distribution on the body and no mutation detected in blood, it is worthwhile to search for a shared PTCH1 mutation in their BCCs as this can detect postzygotic mosaicism. This information is important to ensure proper surveillance programmes, choose the right therapy and provide adequate genetic counselling.

New mutations and an updated database for the patched-1 (PTCH1) gene

BACKGROUND

Basal cell nevus syndrome (BCNS) is an autosomal dominant disorder characterized by multiple basal cell carcinomas (BCCs), maxillary keratocysts, and cerebral calcifications. BCNS most commonly is caused by a germline mutation in the patched-1 (PTCH1) gene. PTCH1 mutations are also described in patients with holoprosencephaly.

METHODS

We have established a locus-specific database for the PTCH1 gene using the Leiden Open Variation Database (LOVD). We included 117 new PTCH1 variations, in addition to 331 previously published unique PTCH1 mutations. These new mutations were found in 141 patients who had a positive PTCH1 mutation analysis in either the VU University Medical Centre (VUMC) or Maastricht University Medical Centre (MUMC) between 1995 and 2015.

RESULTS

The database contains 331 previously published unique PTCH1 mutations and 117 new PTCH1 variations.

CONCLUSION

We have established a locus-specific database for the PTCH1 gene using the Leiden Open Variation Database (LOVD). The database provides an open collection for both clinicians and researchers and is accessible online at http://www.lovd.nl/PTCH1.

Update on Genetic Conditions Affecting the Skin and the Kidneys

Genetic conditions affecting the skin and kidney are clinically and genetically heterogeneous, and target molecular components present in both organs. The molecular pathology involves defects of cell-matrix adhesion, metabolic or signaling pathways, as well as tumor suppressor genes. This article gives a clinically oriented overview of this group of disorders, highlighting entities which have been recently described, as well as the progress made in understanding well-known entities. The genetic bases as well as molecular cell biological mechanisms are described, with therapeutic applications.