A novel mutation in the GDAP1 gene is associated with autosomal recessive Charcot-Marie-Tooth disease in an Amish family

Impaired Mitochondrial Mobility in Charcot-Marie-Tooth Disease

Charcot-Marie-Tooth (CMT) disease is a progressive, peripheral neuropathy and the most commonly inherited neurological disorder. Clinical manifestations of CMT mutations are typically limited to peripheral neurons, the longest cells in the body. Currently, mutations in at least 80 different genes are associated with CMT and new mutations are regularly being discovered. A large portion of the proteins mutated in axonal CMT have documented roles in mitochondrial mobility, suggesting that organelle trafficking defects may be a common underlying disease mechanism. This review will focus on the potential role of altered mitochondrial mobility in the pathogenesis of axonal CMT, highlighting the conceptional challenges and potential experimental and therapeutic opportunities presented by this "impaired mobility" model of the disease.

Childhood onset homozygous recessive GDAP1 (p.Pro231Leu) mutation in a 9-year-old puerto rican pediatric female with axonal Charcot-Marie-Tooth disease: A case report

Charcot-Marie-Tooth disease (CMT) is a progressive hereditary neuromuscular neuropathy with pathology in the myelin sheath or the axon. CMT caused by mutations in the Ganglioside-induced differentiation associated protein 1 (GDAP1) gene has been described by a spectrum of phenotypic presentations. GDAP1 is a mitochondrial protein responsible for protecting neuronal bodies from oxidative stress. It is associated with axonal and demyelinating pathophysiology with recessive and dominant modes of inheritance.We describe a case of a 9-year-old Puerto Rican female with clinical and electrodiagnostic results compatible with an axonal sensory-motor neuropathy where a genetic test describes a homozygous GDAP1 missense mutation at the c.692C>T (p.Pro231Leu), previously undetected in a pediatric Latino patient. Mutations in GDAP1 have been previously described in Tunisian, Old Order Amish, European and Japanese families with varying modes of inheritance. To our knowledge, this homozygous variant presentation of the GDAP1 gene is the first to be described in a pediatric Puerto Rican patient without a family history of hereditary sensory motor neuropathy.

A founder mutation in BBS2 is responsible for Bardet-Biedl syndrome in the Hutterite population: utility of SNP arrays in genetically heterogeneous disorders

Bardet-Biedl syndrome (BBS) is a multisystem genetically heterogeneous disorder, the clinical features of which are largely the consequence of ciliary dysfunction. BBS is typically inherited in an autosomal recessive fashion, and mutations in at least 14 genes have been identified. Here, we report the identification of a founder mutation in the BBS2 gene as the cause for the increased incidence of this developmental disorder in the Hutterite population. To ascertain the Hutterite BBS locus, we performed a genome-wide single nucleotide polymorphism (SNP) analysis on a single patient and his three unaffected siblings from a Hutterite family. The analysis identified two large SNP blocks that were homozygous in the patient but not in his unaffected siblings, one of these regions contained the BBS2 gene. Sequence analysis and subsequent RNA studies identified and confirmed a novel splice site mutation, c.472-2A>G, in BBS2. This mutation was also found in homozygous form in three subsequently studied Hutterite BBS patients from two different leuts, confirming that this is a founder mutation in the Hutterite population. Further studies are required to determine the frequency of this mutation and its role, if any, in the expression of other ciliopathies in this population.

The homozygous ganglioside-induced differentiation-associated protein 1 mutation c.373C > T causes a very early-onset neuropathy: case report and literature review

Mutations in the ganglioside-induced differentiation-associated protein 1 (GDAP1) gene may cause severe early-onset inherited neuropathies. Here, the authors report a clinical and neurophysiological follow-up of a Pakistani child with a very early-onset neuropathy carrying a novel homozygous mutation in the GDAP1gene. They discuss the relationship between the several forms of Charcot-Marie-Tooth disease presenting in the first months of life and focus on the literature of GDAP1-associated early-onset neuropathy. This case further expands on the clinical spectrum and the genetic heterogeneity of early-onset inherited neuropathy due to GDAP1 gene mutations.

Homozygous frameshift mutation in TMCO1 causes a syndrome with craniofacial dysmorphism, skeletal anomalies, and mental retardation

We identified an autosomal recessive condition in 11 individuals in the Old Order Amish of northeastern Ohio. The syndrome was characterized by distinctive craniofacial dysmorphism, skeletal anomalies, and mental retardation. The typical craniofacial dysmorphism included brachycephaly, highly arched bushy eyebrows, synophrys, long eyelashes, low-set ears, microdontism of primary teeth, and generalized gingival hyperplasia, whereas Sprengel deformity of scapula, fusion of spine, rib abnormities, pectus excavatum, and pes planus represented skeletal anomalies. The genome-wide homozygosity mapping using six affected individuals localized the disease gene to a 3.3-Mb region on chromosome 1q23.3-q24.1. Candidate gene sequencing identified a homozygous frameshift mutation, c.139_140delAG, in the transmembrane and coiled-coil domains 1 (TMCO1) gene, as the pathogenic change in all affected members of the extended pedigree. This mutation is predicted to result in a severely truncated protein (p.Ser47Ter) of only one-fourth the original length. The TMCO1 gene product is a member of DUF841 superfamily of several eukaryotic proteins with unknown function. The gene has highly conserved amino acid sequence and is universally expressed in all human tissues examined. The high degree of conservation and the ubiquitous expression pattern in human adult and fetal tissues suggest a critical role for TMCO1. This report shows a TMCO1 sequence variant being associated with a genetic disorder in human. We propose "TMCO1 defect syndrome" as the name of this condition.