A novel homozygous pathogenic missense variant in COX6B1: Further delineation of the phenotype.

Cytochrome c oxidase (COX) deficiency is a phenotypically diverse group of diseases caused by variants in over 30 genes. Biallelic pathogenic variants in COX6B1 have been described in four patients to date with varying disease manifestations. We describe the clinical features and follow-up of a patient with a novel homozygous pathogenic variant in COX6B1 who presented acutely with severe encephalomyopathy associated with an infection. New findings include ophthalmological evaluation and follow-up of neuroradiological investigations. The novel p.Trp31Arg variant was predicted to be pathogenic in silico, and further functional analyses with biochemical analysis of mitochondrial function showed isolated COX deficiency. Muscle biopsy showed a specific lack of COX6B1 protein together with complex IV deficiency on western blot, enzyme histochemistry, and immuno-histochemistry.

Drug-induced hyperthermia with rhabdomyolysis in CLN3 disease.

CLN3 disease (MIM# 204200), the most prevalent of the neuronal ceroid lipofuscinoses (NCL), is an autosomal recessive disorder with juvenile onset characterized by blindness, epilepsy, dementia, psychiatric manifestations, and motor deterioration. Problems related to behavior, emotions and thought are among the main features. Antidepressant and antipsychotic drugs have been employed with variable results. Neuroleptic malignant syndrome (NMS) has previously been described in two patients with NCL, one with CLN3 disease and one with adult onset NCL of unclear genetic origin. Our aims were to describe the occurrence of drug-induced hyperthermia in pediatric patients with CLN3 disease from West and South Sweden and to delineate the range of associated clinical features. Our study identified four patients presenting with seven episodes of severe drug-induced hyperthermia and either NMS-like or Serotonin syndrome (SS)-like features. Possibly provoking drugs were risperidone, clozapine, olanzapine, haloperidol, quetiapine, and sertraline. The course was atypical, frequently prolonged, associated with rhabdomyolysis and status dystonicus, and resulted in the death of three of the patients. Our study points to a vulnerability to drug-induced hyperthermia in patients with CLN3 disease which we believe could be underreported. Interestingly the proposed pathophysiological mechanisms behind NMS and SS on one hand and CLN3 on the other hand seem to converge in a common mechanism involving dysregulation of the sympathetic nervous system.

Noonan and cardio-facio-cutaneous syndromes: two clinically and genetically overlapping disorders.

BACKGROUND: Noonan syndrome (NS) and cardio-facio-cutaneous syndrome (CFC) are related disorders associated with disrupted RAS/RAF/MEK/ERK signalling. NS, characterised by facial dysmorphism, congenital heart defects and short stature, is caused by mutations in the genes PTPN11, SOS1, KRAS and RAF1. CFC is distinguished from NS by the presence of ectodermal abnormalities and more severe mental retardation in addition to the NS phenotype. The genetic aetiology of CFC was recently assigned to four genes: BRAF, KRAS, MEK1 and MEK2. METHODS: A comprehensive mutation analysis of BRAF, KRAS, MEK1, MEK2 and SOS1 in 31 unrelated patients without mutations in PTPN11 is presented. RESULTS: Mutations were identified in seven patients with CFC (two in BRAF, one in KRAS, one in MEK1, two in MEK2 and one in SOS1). Two mutations were novel: MEK1 E203Q and MEK2 F57L. The SOS1 E433K mutation, identified in a patient diagnosed with CFC, has previously been reported in patients with NS. In one patient with NS, we also identified a mutation, BRAF K499E, that has previously been reported in patients with CFC. We thus suggest involvement of BRAF in the pathogenesis of NS also. CONCLUSIONS: Taken together, our results indicate that the molecular and clinical overlap between CFC and NS is more complex than previously suggested and that the syndromes might even represent allelic disorders. Furthermore, we suggest that the diagnosis should be refined to, for example, NS-PTPN11-associated or CFC-BRAF-associated syndromes after the genetic defect has been established, as this may affect the prognosis and treatment of the patients.