Rebecca Ionasescu

Mutations of the noncoding region of the connexin32 gene in X-linked dominant Charcot-Marie-Tooth neuropathy

We studied two families with X-linked dominant Charcot-Marie-Tooth neuropathy. The clinical findings included onset around age 14 years, with moderate weakness of feet extensors and palmar and dorsal interossei, areflexia, distal hypesthesia, and slow progressivity. Motor nerve conduction velocities showed slowing (20 to 30 m/sec) and EMGs were normal. Genetic linkage analysis revealed positive lod scores with the markers of the Xq13.1 region in family 2, but was noninformative in family 1. There were no point mutations in the connexin32 gene coding region. Instead, family 1 revealed a T-to-G transversion at position -528 relative to the ATG start codon, whereas family 2 showed a C-to-T transition at position -458. The first mutation is located in the nerve-specific connexin32 promoter just upstream of the transcription start site, the second is located in the 5 prime untranslated region of the mRNA. NEUROLOGY 1996;47: 541-544

Localization of the gene for X‐linked spinal muscular atrophy

We used probes for DNA polymorphisms on the X chromosome to study genetic linkage in seven families with X-linked adult-onset spinal muscular atrophy. We found significant linkage to the marker DXYS1 on the proximal X chromosome long arm and loose linkage or nonlinkage to markers elsewhere. Our analysis localizes the gene defect for this form of anterior horn cell disease.

Dejerine-Sottas disease with de novo dominant point mutation of the PMP22 gene

We studied a 33-year-old woman with a negative family history. Both of her parents were examined clinically by nerve conduction velocities (NCVs) and EMG, with normal results. The clinical onset of her condition was at 24 months, with severe weakness and atrophy of her feet and hands, but the proximal muscles were relatively spared. She had bilateral pes cavus, distal weakness and hypesthesia for touch and proprioception, areflexia, claw hands, and severe thoracolumbar kyphoscoliosis. NCVs showed absent motor and sensory responses and EMG revealed diffuse fibrillation potentials. Molecular genetic studies indicated a de novo dominant missense point mutation of exon 3 of the peripheral myelin protein 22 gene at nucleotide 264 that caused the replacement of serine with leucine. NEUROLOGY 1995;45: 1766-1767

Inherited ophthalmoplegia with intestinal pseudo-obstruction

A new inherited neuromuscular disease was identified in 4 patients (1 male, 3 females), offspring of consanguineous marriages, belonging to the same kindred. The proband was a 24-year-old female with history of ptosis and ophthalmoplegia since childhood and progressive intestinal pseudo-obstruction for the last 4 years of her life. A sural nerve biopsy showed axonal and demyelinating neuropathy. Muscle biopsies of pectoral and gastrocnemius revealed myopathic alterations with marked variation in muscle fiber size, atrophy of both fiber types and normal mitochondria. An upper gastrointestinal study showed barium in the stomach after 8 h and jejunal diverticula. Tests for absorption of fat, protein, carbohydrate, folic acid and vitamin B12 were normal. Serum levels of vitamin A and lipoproteins were also normal. The patient underwent partial gastrectomy and gastrojejunostomy. Postoperatively, she developed severe pancreatitis, sepsis, peritonitis and expired. Tissue samples from the proband and from her brother, revealed normal mucosa, but degeneration of smooth muscle of the stomach and small intestine. The myenteric plexus and vagus nerves were normal. The biochemical studies of contractile proteins (myosin, actin, tropomyosin) in the fresh and cultured smooth muscle cells of the proband obtained at the time of gastrectomy showed a 50-75% decrease in the synthesis of different contractile proteins. Turnover of contractile proteins and synthesis and turnover of collagen showed normal values. The reduction in synthesis of contractile proteins may account for the weak peristalsis and be a factor in the pathogenesis of the intestinal pseudo-obstruction.

Increased collagen synthesis by Duchenne myogenic clones

Myogenic cell clones were grown in triplicates from 3 patients with Duchenne muscular dystrophy, 5 with late onset myotonic dystrophy, 2 with spinal muscular atrophy, 6 male children controls, 4 adult controls and 6 normal aborted fetuses (10-12 weeks old). The clones from patients with myotonic dystrophy and spinal muscular atrophy had normal collagen synthesis. The fetal clones showed 3.3-fold lower values than control clones for [3H] extracellular (medium) hydroxyproline, while intracellular [3H] hydroxyproline levels showed normal values. Analysis of [3H] proline incorporation demonstrated a 4-fold increase in [3H] hydroxyproline released into the medium of Duchenne myogenic cell clones while intracellular [3H] hydroxyproline levels showed normal values. The collagen turnover of Duchenne clones was normal. These results strongly suggest that the increased amount of collagen present in Duchenne dystrophic muscle is related to the primary defect of the disease and is not due to secondary replacement fibrosis.

Mapping of the gene for X-linked dominant Charcot-Marie-Tooth neuropathy

We performed a clinical study and linkage analysis on 278 subjects (66 affected) belonging to eight families with X-linked dominant Charcot-Marie-Tooth (CMT) neuropathy. This form affects 11.8% of CMT patients in Iowa. Motor nerve conduction velocities (MNCVs) were significantly slowed consistent with type 1 CMT. Fifty-six obligate carriers manifested mild distal weakness, localized areflexia, pes cavus, and slowing on MNCVs. Seven X-linked restriction fragment length polymorphisms mapping in the Xpll-q 21 region were tested for linkage against CMT. Two-point linkage results showed the highest low scores with PGK1, DXS159, and DXYS1. Multipoint linkage analysis excluded the CMT gene from being telomeric to either DXS14 or DXYS1, with over 1,000:1 odds. The highest location scores were at PGK1 and 1 cM proximal to DXS159.

A Dejerine-Sottas neuropathy family with a gene mapped on chromosome 8

The patient is a 55‐year‐old black male who belongs to a large family with 9 affected relatives with autosomal dominant Dejerine‐Sottas neuropathy (DSN). Onset of his condition was at 2 years of age with steppage gait followed by severe progressive weakness, atrophy, and sensory loss of his legs and hands accompanied by areflexia and thoracolumbar kyphoscoliosis. The patient became wheelchair‐confined at age 38. At around age 42, the left shoulder became dislocated and the humeral head underwent aseptic necrosis (Charcot joint). Nerve conduction studies showed absent motor and sensory responses for all major nerves tested. Genetic linkage suggested mapping of this DSN gene on chromosome 8qter. A younger brother with similar neurological findings also demonstrated Charcot joints with bone destruction of the joints of the fourth and fifth fingers.

Alterations in lipid incorporation in Duchenne muscular dystrophy ☆: Studies of fresh and cultured muscle

The incorporation of [3H] glycerol into lipids of fresh and cultured skeletal muscle obtained from patients with Duchenne muscular dystrophy (DMD), patients with myotonic dystrophy (My Dyst), controls, and aborted fetuses (10-12 weeks old) was studied. A significant increase of specific incorporation of [3H] glycerol into phosphatidylcholine (PCh), phosphatidylserine (PS), phosphatidylinositol (PI), and triglycerides (TRI) was found in DMD and fetal muscle in both fresh and cultured muscle. No significant differences, however, were noted between the values of glycerol incorporation in DMD and fetal muscle. The ratio between phospholipids and TRI changed significantly for fresh muscle in DMD (3.5) and fetal muscle (4.9) versus controls (24). The incorporation of glycerol into these lipids in My Dyst fresh and cultured muscle showed the same value as controls when expressed both as incorporation/mg protein and ratio between phospholipids and TRI.

Linkage analysis of Charcot-Marie-Tooth neuropathy (HMSN type I)

Fifteen HMSN families with 218 members and documented male-to-male transmission and slow motor nerve conduction velocities were informative for linkage to Duffy blood group (Fy), antithrombin III cDNA probe (AT3) and renin (REN). Our data support linkage to Fy in 8 families (lod score = 2.45 at theta = 0) consistent with HMSN type IB. Linkage to AT3 (lod score = 1.28 at theta = 0) and linkage of Fy to AT3 (lod score = 1.61 at theta = 0) is also supported in 3 of the 8 original families. Linkage to REN (lod score = 0.78 at theta = 0), linkage of Fy to REN (lod score = 0.89 at theta = 0), and linkage of AT3 to REN (lod score = 0.88 at theta = 0) is supported in only 2 of the 8 original families. Linkage to Fy was rejected in seven families, consistent with HMSN type IA (lod score = -4.34 at theta = 0.05). Linkage to AT3 was rejected in 12 families (lod score = -9.52 at theta = 0.05). Linkage to REN was rejected in 13 families (lod score = -11.07 at theta = 0.05). Our data provide support for the concept of genetic heterogeneity in CMT hypertrophic neuropathy (HMSN type I). The linkage of HMSN type IB to Fy seems to be tighter than to AT3 and REN, strongly suggesting the mapping of HMSN type IB locus on the proximal part of the long arm of chromosome 1, close to the centromere.

Consortium Fine Localization of X-Linked Charcot-Marie-Tooth Disease (CMTX1): Additional Support that Connexin32 Is the Defect in CMTX1

Charcot-Marie-Tooth (CMT) disease is the most common form of inherited motor and sensory neuropathy. X-linked CMT (CMTX1) has been localized to the pericentric region of the X chromosome. Recently, mutations have been defined in the connexin32 gene that cosegregate with the CMTX1 phenotype in several families. The present paper presents the results of an international consortium to fine map the gene for CMTX1 to a small segment of Xq12-13. The linkage data, together with the molecular genetic studies, support the hypothesis that connexin32 is the genetic defect in CMTX1.