Griscelli syndrome

Griscelli syndrome is a rare autosomal childhood disorder characterised by albinism (hypopigmentation).

Types

 * Type I Griscelli syndrome -- MYO5A
 * Type II Griscelli syndrome is caused by the knock out of the gene for Rab27A and is characterised by hypopigmentation and immunodeficiency. Children with this syndrome die with a mean age of 5 years. The only cure is bone-marrow transplantation. To date approximately 10 children have received successful bone marrow transplants for type II Griscelli syndrome.
 * Type III Griscelli syndrome -- melanophilin, MYO5A

Presentation
Griscelli syndrome is defined by the characteristic hypopigmentation. This may be caused by the loss of three different genes, each of which has different additional effects, resulting in the three types of syndrome.

Pathophysiology
In melanocytes, melanosomes (vesicles containing the pigment melanin) are transported on microtubules. They are then bound by Rab27A which recruits Slac2-a and myosin Va. This complex then transfers the melanosomes from the microtubules to actin filaments. This transfer is necessary for the transport of melanosomes from the perinuclear area to the cell periphery. The loss of any one of these proteins interrupts melanosome transport and results in the hypopigmentation.

However, these three proteins do not work together in other cells and Rab27A effectors may be 'mix and match' For example the knockout of Rab27 causes the hypopigmentation but also immunodeficiency due to deficiencies in cytotoxic killing activity in cytotoxic T cells (something that also depends on vesicle transport). While, the knockout of myosin Va does not cause immunodeficiency, but it does cause neural defects. Though some neural problems (i.e brain damage) can be seen in Rab27A deficient children, this is thought to be a secondary effect of the immune problems, and not directly due to the lack of Rab27A.

Eponym
It is named for Claude Griscelli.