Genetic refinement of the hereditary neuralgic amyotrophy (HNA) locus at chromosome 17q25

Hereditary neuralgic amyotrophy in childhood caused by duplication within the SEPT9 gene: A family study

Hereditary neuralgic amyotrophy (HNA) is an autosomal dominant disorder associated with episodic, recurrent, and painful neuropathies affecting the nerves of the brachial plexus. In this study, we report on a family of Lebanese descent with HNA onset in early childhood. The affected family members presented with platelet dysfunction. Platelet aggregation was reduced after stimulation with the agonists ADP and epinephrine in all affected family members. Flow cytometric analyses revealed impaired platelet δ‐secretion. The index patient and one brother suffered from kidney cysts. Molecular genetic analysis revealed a heterozygous duplication of exon 2 within the septin 9 (SEPT9) gene in all the affected family members. Such a young child with HNA (aged 2 years) caused by SEPT9 duplication has not been described so far.

Duplication within the SEPT9 gene associated with a founder effect in North American families with hereditary neuralgic amyotrophy

Hereditary neuralgic amyotrophy (HNA) is an autosomal dominant disorder associated with recurrent episodes of focal neuropathy primarily affecting the brachial plexus. Point mutations in the SEPT9 gene have been previously identified as the molecular basis of HNA in some pedigrees. However in many families, including those from North America demonstrating a genetic founder haplotype, no sequence mutations have been detected. We report an intragenic 38 Kb SEPT9 duplication that is linked to HNA in 12 North American families that share the common founder haplotype. Analysis of the breakpoints showed that the duplication is identical in all pedigrees, and molecular analysis revealed that the duplication includes the 645 bp exon in which previous HNA mutations were found. The SEPT9 transcript variants that span this duplication contain two in-frame repeats of this exon, and immunoblotting demonstrates larger molecular weight SEPT9 protein isoforms. This exon also encodes for a majority of the SEPT9 N-terminal proline rich region suggesting that this region plays a role in the pathogenesis of HNA.

Inherited focal, episodic neuropathies: hereditary neuropathy with liability to pressure palsies and hereditary neuralgic amyotrophy

Hereditary neuropathy with liability to pressure palsies (HNPP; also called tomaculous neuropathy) is an autosomal-dominant disorder that produces a painless episodic, recurrent, focal demyelinating neuropathy. HNPP generally develops during adolescence, and may cause attacks of numbness, muscular weakness, and atrophy. Peroneal palsies, carpal tunnel syndrome, and other entrapment neuropathies may be frequent manifestations of HNPP. Motor and sensory nerve conduction velocities may be reduced in clinically affected patients, as well as in asymptomatic gene carriers. The histopathological changes observed in peripheral nerves of HNPP patients include segmental demyelination and tomaculous or "sausage-like" formations. Mild overlap of clinical features with Charcot-Marie-Tooth (CMT) disease type 1 (CMT1) may lead patients with HNPP to be misdiagnosed as having CMT1. HNPP and CMT1 are both demyelinating neuropathies, however, their clinical, pathological, and electrophysiological features are quite distinct. HNPP is most frequently associated with a 1.4-Mb pair deletion on chromosome 17p12. A duplication of the identical region leads to CMT1A. Both HNPP and CMT1A result from a dosage effect of the PMP22 gene, which is contained within the deleted/duplicated region. This is reflected in reduced mRNA and protein levels in sural nerve biopsy samples from HNPP patients. Treatment for HNPP consists of preventative and symptom-easing measures. Hereditary neuralgic amyotrophy (HNA; also called familial brachial plexus neuropathy) is an autosomal-dominant disorder causing episodes of paralysis and muscle weakness initiated by severe pain. Individuals with HNA may suffer repeated episodes of intense pain, paralysis, and sensory disturbances in an affected limb. The onset of HNA is at birth or later in childhood with prognosis for recovery usually favorable; however, persons with HNA may have permanent residual neurological dysfunction following attack(s). Episodes are often triggered by infections, immunizations, the puerperium, and stress. Electrophysiological studies show normal or mildly prolonged motor nerve conduction velocities distal to the affected brachial plexus. Pathological studies have found axonal degeneration in nerves examined distal to the plexus abnormality. In some HNA pedigrees there are characteristic facial features, including hypotelorism. The prognosis for recovery of normal function of affected limbs in HNA is good, although recurrent episodes may cause residual deficits. HNA is genetically linked to chromosome 17q25, where mutations in the septin-9 (SEPT9) gene have been found.

Mutations in SEPT9 cause hereditary neuralgic amyotrophy

Hereditary neuralgic amyotrophy (HNA) is an autosomal dominant recurrent neuropathy affecting the brachial plexus. HNA is triggered by environmental factors such as infection or parturition. We report three mutations in the gene septin 9 (SEPT9) in six families with HNA linked to chromosome 17q25. HNA is the first monogenetic disease caused by mutations in a gene of the septin family. Septins are implicated in formation of the cytoskeleton, cell division and tumorigenesis.

Genomic organization and mutation analysis of three candidate genes for hereditary neuralgic amyotrophy

Hereditary neuralgic amyotrophy (HNA) is an autosomal-dominant inherited recurrent focal neuropathy affecting mainly the brachial plexus. In this study we report the genomic structure and mutation analysis of three candidate genes: sphingosine kinase 1 (SPHK1); tissue inhibitor of metalloproteinase 2 (TIMP2); and cytoglobin (CYGB). We did not find any disease-associated mutations, indicating that HNA is not caused by point mutations in these genes. However, we identified several sequencing errors in the cDNA of SPHK1 as well as seven novel single-nucleotide polymorphisms.

Chapter 24 Genetic evaluation of inherited motor/sensory neuropathy

Inherited disorders of peripheral nerves represent a common group of neurologic diseases. Charcot-Marie-Tooth neuropathy type 1 (CMT1) is a genetically heterogeneous group of chronic demyelinating polyneuropathies with loci mapping to chromosome 17 (CMT1A), chromosome 1 (CMT1B), chromosome 16 (CMT1C) and chromosome 10 (CMT1D). CMT1A is most often associated with a tandem 1.5-megabase (Mb) duplication in chromosome 17p11.2-p12. In rare patients it may result from a point mutation in the peripheral myelin protein-22 (PMP22) gene. CMT1B is associated with point mutations in the myelin protein zero (Po or MPZ) gene. Mutations in the SIMPLE gene cause CMT1C, and CMT1D is the result of mutations in the early response 2 (ERG2 or Krox-20) gene. An X-linked form of CMT1 (CMT1X) maps to Xq13 and is associated with mutations in the connexin32 (Cx32) gene. Charcot-Marie-Tooth neuropathy type 2 (CMT2) is an axonal neuropathy that maps to chromosome 1p35-p36 (CMT2A), chromosome 3q13-q22 (CMT2B), chromosome 7p14 (CMT2D), chromosome 8p21 (CMT2E), chromosome 1q22-q23 (CMT2F) or chromosome 3q13 (CMT2G). Two X-linked forms of CMT2 have been reported (CMT2XA and CMT2XB), but the genes remain unidentified. An area that has recently expanded is the identification of autosomal recessive forms of CMT type 1 and 2. Of the eight recessive forms of CMT1 that have been identified to date, only two have been fully characterized at the molecular level (CMT1 AR B 1 and CMT1 AR D). Point mutations were found in the myotubularin-related protein-2 (MTM2) gene for CMT1 AR B1. CMT1 AR D is the result of point mutations in the N-myc downstream-regulated gene 1 (NDRG1). Dejerine-Sottas disease (DSD), also called hereditary motor and sensory neuropathy type III (HMSNIII), is a severe, infantile-onset demyelinating polyneuropathy syndrome that may be associated with point mutations in either the PMP22 gene, PO gene, EGR2 gene or the PRX gene (for the recessive form). It shares considerable clinical and pathological features with CMT1. Hereditary neuropathy with liability to pressure palsies (HNPP) is an autosomal dominant disorder that results in a recurrent, episodic demyelinating neuropathy. HNPP is associated with a 1.5-Mb deletion in chromosome 17p11.2-p12 that results in reduced expression of the PMP22 gene. CMT1A and HNPP are reciprocal duplication/deletion syndromes that originate from unequal crossover during germ cell meiosis. Other rare forms of demyelinating peripheral neuropathies map to chromosome 8q, 10q and 11q.

Brachial plexus involvement as the only expression of hereditary neuropathy with liability to pressure palsies

Hereditary neuropathy with liability to pressure palsies (HNPP) is an autosomal-dominant focal neuropathy characterized by recurrent entrapment neuropathies. Single members of families with HNPP and brachial plexus involvement have been reported previously. We describe a family with three affected members and in which the only symptom of entrapment was recurrent brachial plexopathy. The diagnosis of HNPP in this family was confirmed by both neurophysiological methods and DNA analysis. The distinction between HNPP and hereditary neuralgic amyotrophy is discussed.