Friedreich's ataxia (FRDA) is an autosomal recessive, degenerative disease that involves the central and peripheral nervous systems and the heart. A gene, X25 , was identified in the critical region for the FRDA locus on chromosome 9q13. The gene encodes a 210-amino acid protein, frataxin, that has homologs in distant species such as Caenorhabditis elegans and yeast. A few FRDA patients were found to have point mutations in X25 , but the majority were homozygous for an unstable GAA trinucleotide expansion in the first X25 intron.

Objective: Intestinal dysbiosis has been associated with coeliac disease (CD), but whether the alterations are cause or consequence of the disease is unknown. This study investigated whether the human leukocyte antigen (HLA)-DQ2 genotype is an independent factor influencing the early gut microbiota composition of healthy infants at family risk of CD. Design: As part of a larger prospective study, a subset (n=22) of exclusively breastfed and vaginally delivered infants with either high genetic risk (HLA-DQ2 carriers) or low genetic risk (non-HLA-DQ2/8 carriers) of developing CD were selected from a cohort of healthy infants with at least one first-degree relative with CD. Infant faecal microbiota was analysed by 16S rRNA gene pyrosequencing and real time quantitative PCR. Results: Infants with a high genetic risk had significantly higher proportions of Firmicutes and Proteobacteria and lower proportions of Actinobacteria compared with low-risk infants. At genus level, high-risk infants had significantly less Bifidobacterium and unclassified Bifidobacteriaceae proportions and more Corynebacterium, Gemella, Clostridium sensu stricto, unclassified Clostridiaceae, unclassified Enterobacteriaceae and Raoultella proportions. Quantitative real time PCR also revealed lower numbers of Bifidobacterium species in infants with high genetic risk than in those with low genetic risk. In high-risk infants negative correlations were identified between Bifidobacterium species and several genera of Proteobacteria (Escherichia/Shigella) and Firmicutes (Clostridium). Conclusions: The genotype of infants at family risk of developing CD, carrying the HLA-DQ2 haplotypes, influences the early gut microbiota composition. This finding suggests that a specific disease-biased host genotype may also select for the first gut colonisers and could contribute to determining disease risk.

Mutations in GDAP1, the ganglioside-induced differentiation-associated protein 1 gene, cause Charcot–Marie–Tooth (CMT) type 4A, a severe autosomal recessive form of neuropathy associated with either demyelinating or axonal phenotypes. Here, we demonstrate that GDAP1 has far greater expression in neurons than in myelinating Schwann cells. We investigated cell localization of GDAP1 in a human neuroblastoma cell line by means of transient overexpression and co-localization with organelle markers in COS-7 cells and by western blot analysis of subcell fractions with anti-GDAP1 polyclonal antibodies. We observed that GDAP1 is localized in mitochondria. We also show that C-terminal transmembrane domains are necessary for the correct localization in mitochondria; however, missense mutations do not change the mitochondrial pattern of the wild-type protein. Our findings suggest that CMT4A disease is in fact a mitochondrial neuropathy mainly involving axons and represents a disease belonging to the new category of mitochondrial disorders caused by mutations in nuclear genes. We postulate that GDAP1 may be related to the maintenance of the mitochondrial network.

Autosomal recessive cerebellar ataxias (ARCA) are a heterogeneous group of rare neurological disorders involving both central and peripheral nervous system, and in some case other systems and organs, and characterized by degeneration or abnormal development of cerebellum and spinal cord, autosomal recessive inheritance and, in most cases, early onset occurring before the age of 20 years. This group encompasses a large number of rare diseases, the most frequent in Caucasian population being Friedreich ataxia (estimated prevalence 2-4/100,000), ataxia-telangiectasia (1-2.5/100,000) and early onset cerebellar ataxia with retained tendon reflexes (1/100,000). Other forms ARCA are much less common. Based on clinicogenetic criteria, five main types ARCA can be distinguished: congenital ataxias (developmental disorder), ataxias associated with metabolic disorders, ataxias with a DNA repair defect, degenerative ataxias, and ataxia associated with other features. These diseases are due to mutations in specific genes, some of which have been identified, such as frataxin in Friedreich ataxia, alpha-tocopherol transfer protein in ataxia with vitamin E deficiency (AVED), aprataxin in ataxia with oculomotor apraxia (AOA1), and senataxin in ataxia with oculomotor apraxia (AOA2). Clinical diagnosis is confirmed by ancillary tests such as neuroimaging (magnetic resonance imaging, scanning), electrophysiological examination, and mutation analysis when the causative gene is identified. Correct clinical and genetic diagnosis is important for appropriate genetic counseling and prognosis and, in some instances, pharmacological treatment. Due to autosomal recessive inheritance, previous familial history of affected individuals is unlikely. For most ARCA there is no specific drug treatment except for coenzyme Q10 deficiency and abetalipoproteinemia.

Background: Mutations in the ganglioside-induced differentiation-associated protein 1 gene (GDAP1) were recently shown to be responsible for autosomal recessive (AR) demyelinating Charcot–Marie–Tooth disease (CMT) type 4A (CMT4A) as well as AR axonal CMT with vocal cord paralysis. Methods: The coding region of GDAP1 was screened for the presence of mutations in seven families with AR CMT in which the patients were homozygous for markers of the CMT4A locus at chromosome 8q21.1. Results: A nonsense mutation was detected in exon 5 (c.581C>G, S194X), a 1-bp deletion in exon 6 (c.786delG, G262fsX284), and a missense mutation in exon 6 (c.844C>T, R282C). Conclusions: Mutations in GDAP1 are a frequent cause of AR CMT. They result in an early-onset, severe clinical phenotype. The range of nerve conduction velocities (NCV) is variable. Some patients have normal or near normal NCV, suggesting an axonal neuropathy, whereas others have severely slowed NCV compatible with demyelination. The peripheral nerve biopsy findings are equally variable and show features of demyelination and axonal degeneration.