Genetic analysis of Café-au-Lait skin cells and their potential to develop into FD/MAS affected bones

Fibrous Dysplasia (FD) is a rare bone disease, characterized by a mutated
G-protein alpha subunit (GNAS) gene. This mutation leads to abnormal bone
matrix synthesis and thus to fibro-osseous bone lesions. Café-au-Lait skin
macules are characteristic for patients with the McCune-Albright Syndrome, a
variant of FD (FD/MAS). Patients with FD/MAS can experience intense pain and
encounter a high risk of bone fractures and bone deformities during their whole
life. On top of this, hyperfunctional endocrinopathies reduce their quality of
life as well. To date, no cure exists.
Relatively little research has been conducted on this disease because of the
invasiveness of bone biopsies, the risk of further expansion of the lesion
after taking the biopsy, and the low number of patients. However, Micha et al.
(2016) have recently shown the suitability of fibroblasts from skin biopsies to
study aberrant bone formation in patients with Fibrodysplasia Ossificans
Progressiva (FOP), another rare bone disease. To accomplish this, they
transdifferentiated these fibroblasts towards the osteogenic lineage. We
hypothesize that the same approach using skin biopsies from *Café* spots
(hyperpigmented skin), control sites, i.e. *Lait* spots (non-hyperpigmented
skin) and those from birthmarks of FD/MAS patients (outside the Café spots)
will allow us to study abnormal bone formation of FD/MAS patients.
Three 4 mm diameter skin biopsies (see above) per FD/MAS patient will be taken.
The intended goal is to recruit five participants within three months. The
Fibrous Dysplasia association, with whom the VUmc has close contact, will be
asked to help in the recruitment. Recruitment will be done via the Amsterdam
University Medical Centers, location VUmc, expertise center in rare bone
diseases. The epidermal layer and dermis will be separated and studied for the
presence of the GNAS mutation. Subsequently, osteogenic transdifferentiation
possibilities of the cultured cells will be evaluated. To identify how FD/MAS
affects osteoblastic differentiation, the functionality of the osteogenic cells
resulting from transdifferentation will be compared between the three skin
biopsy groups (*Café* region, *Lait* region and birthmark).

Objectives:
(1) To find out in which skin layer (epidermis or dermis) and which skin cell
type the Gs* mutation resides.
(2) To determine osteogenic transdifferentiation- and mineralization
characteristics of osteogenic cells that result from transdifferentiated skin
cells.
And to identify whether there is a link between pigmentation and the outcome of
(the functionality of) osteogenic transdifferentation of skin cells.

Single center, non-randomized, analytical observational, cross-sectional pilot
study

Participating patients will visit the hospital for skin biopsies. Patients may
experience some pain after the skin biopsy. A pain reliever such as paracetamol
(acetaminophen) can reduce pain. Sometimes a bruise develops. A minimal chance
of infection is present. Small scars can form on the sites of biopsy
collection. Participants are not restricted during their normal daily
activities after the biopsy is taken. Our risk assessment is: low risk.