Ramon Ruiz-Maldonando

Bio: Ramon Ruiz-Maldonando is an academic researcher. The author has contributed to research in topics: Griscelli syndrome & Hypotonia. The author has an hindex of 1, co-authored 1 publications receiving 56 citations.

Elejalde syndrome--a melanolysosomal neurocutaneous syndrome: clinical and morphological findings in 7 patients.

Abstract: Background Silvery hair and severe dysfunction of the central nervous system (neuroectodermal melanolysosomal disease or Elejalde syndrome) characterize this rare autosomal recessive disease. Main clinical features include silver-leaden hair, bronze skin after sun exposure, and neurologic involvement (seizures, severe hypotonia, and mental retardation). Large granules of melanin unevenly distributed in the hair shaft are observed. Abnormal melanocytes and melanosomes and abnormal inclusion bodies in fibroblasts may be present. Differential diagnosis with Chediak-Higashi syndrome and Griscelli syndrome must be done. Observations We studied pediatric patients with silvery hair and profound neurologic dysfunction. Immune impairment was absent. Age of onset of neurologic signs ranged from 1 month to 11 years; the signs included severe muscular hypotonia, ocular alterations, and seizures. Mental retardation since the first months of life was noted in 4 cases. Psychomotor development was normal in 3 cases, but suddenly the patients presented with a regressive neurologic process. Four patients died between 6 months and 3 years after the onset of neurologic dysfunction. One patient showed characteristic ultrastructural findings of Elejalde syndrome. Conclusions Elejalde syndrome is different from Chediak-Higashi and Griscelli syndrome and is characterized by silvery hair and frequent occurrence of fatal neurologic alterations. Psychomotor impairment may have 2 forms of presentation: congenital or infantile. Although Elejalde syndrome and Griscelli syndrome are similar, the possibility that they are 2 different diseases, although probably allelic related, is suggested.

Griscelli syndrome: a model system to study vesicular trafficking.

Abstract: Griscelli syndrome (GS) is a rare autosomal recessive disorder caused by mutations in either the myosin VA (GS1), RAB27A (GS2) or melanophilin (GS3) genes The three GS subtypes are commonly characterized by pigment dilution of the skin and hair, due to defects involving melanosome transport in melanocytes Here, we review how detailed studies concerning GS have contributed to a better understanding of the molecular mechanisms involved in vesicle transport and membrane trafficking processes Additionally, we demonstrate that the identification and biological analysis of novel disease-causing mutations highlighted the functional importance of the RAB27A-MLPH-MYO5A tripartite complex in intracellular melanosome transport As the small GTPase Rab27a is able to interact with multiple effectors, including Slp2-a and Myrip, we report on their presumed role in melanosome transport Furthermore, we summarize data suggesting that RAB27B and RAB27A are functionally redundant and hereby provide further insight into the pathogenesis of GS2 Finally, we discuss how the gathered knowledge about the RAB27A-MLPH-MYO5A tripartite complex can be translated into a possible therapeutic application to reduce (hyper)pigmentation of the skin

Hermansky–Pudlak Syndrome and Related Disorders of Organelle Formation

Abstract: Hermansky-Pudlak syndrome (HPS) consists of a group of genetically heterogeneous disorders which share the clinical findings of oculocutaneous albinism, a platelet storage pool deficiency, and some degree of ceroid lipofuscinosis. Related diseases share some of these findings and may exhibit other symptoms and signs but the underlying defect in the entire group of disorders involves defective intracellular vesicle formation, transport or fusion. Two HPS-causing genes, HPS1 and ADTB3A, have been isolated but the function of only the latter has been determined. ADTB3A codes for the beta 3A subunit of adaptor complex-3, responsible for vesicle formation from the trans-Golgi network (TGN). The many HPS patients who do not have HPS1 or ADTB3A mutations have their disease because of mutations in other genes. Candidates for these HPS-causing genes include those responsible for mouse models of HPS or for the 'granule' group of eye color genes in Drosophila. Each gene responsible for a subset of HPS or a related disorder codes for a protein which almost certainly plays a pivotal role in vesicular trafficking, inextricably linking clinical and cell biological interests in this group of diseases.

Hypomelanoses and hypermelanoses

Abstract: 9. Tezcan I et al: Successful bone marrow transplantation in a case of Griscelli disease which presented in accelerated phase with neurological involvement. Bone Marrow Transplant 24:931-933, 1999 10. Schuster F et al: Griscelli syndrome: Report of the first peripheral blood stem cell transplant and the role of mutations in the RAB27A gene as an indication for BMT. Bone Marrow Transplant 28:409-412, 2001

Evidence that Griscelli syndrome with neurological involvement is caused by mutations in RAB27A, not MYO5A.

Abstract: Griscelli syndrome (GS), a rare autosomal recessive disorder, is characterized by partial albinism, along with immunologic abnormalities or severe neurological impairment or both. Mutations in one of two different genes on chromosome 15q can cause the different subtypes of GS. Most patients with GS display the hemophagocytic syndrome and have mutations in RAB27A, which codes for a small GTPase. Two patients with neurological involvement have mutations in MYO5A, which codes for an actin-based molecular motor. The RAB27A and MYO5A gene products interact with each other and function in vesicle trafficking. We report the molecular basis of GS in a Muslim Arab kindred whose members have extremely variable neurological involvement, along with the hemophagocytic syndrome and immunologic abnormalities. The patients have normal MYO5A genes but exhibit a homozygous 67.5-kb deletion that eliminates RAB27A mRNA and immunocytofluorescence-detectable protein. We also describe the molecular organization of RAB27A and a multiplex polymerase chain reaction assay for the founder deletion in this kindred. Finally, we propose that all patients with GS have RAB27A mutations and immunologic abnormalities that sometimes result in secondary neurological involvement. The two patients described elsewhere who have MYO5A mutations and neurological complications but no immunologic defects may not have GS but instead may have Elejalde syndrome, a condition characterized by mild hypopigmentation and severe, primary neurological abnormalities.

The role of myosin V in exocytosis and synaptic plasticity

Abstract: In neuroscience, myosin V motor proteins have attracted attention since they are highly expressed in brain, and absence of myosin Va in man leads to a severe neurological disease called Griscelli syndrome. While in some cells myosin V is described to act as a vesicle transport motor, an additional role in exocytosis has emerged recently. In neurons, myosin V has been linked to exocytosis of secretory vesicles and recycling endosomes. Through these functions, it is implied in regulating important brain functions including the release of neuropeptides by exocytosis of large dense-core vesicles and the insertion of neurotransmitter receptors into post-synaptic membranes. This review focuses on the role of myosin V in (i) axonal transport and stimulated exocytosis of large dense-core vesicles to regulate the secretion of neuroactive substances, (ii) tethering of the endoplasmic reticulum at cerebellar synapses to permit long-term depression, (iii) recycling of α-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptors at hippocampal synapses during long-term potentiation, and (iv) recycling of nicotinic acetylcholine receptors at the neuromuscular junction. Myosin V is thus discussed as an important modulator of synaptic plasticity.