Rare myelin protein zero sequence variant in late onset CMT1B.

Myelin protein zero (MPZ) mutations cause demyelinating neuropathies that range from severe neonatal to milder adult forms. We report a 65-year-old woman with slowly progressive leg weakness starting at 47. Examination revealed distal weakness and atrophy in all extremities, impaired light touch in both feet and pin perception to proximal calves, absent leg reflexes, and unsteady gait. Electrodiagnostic studies revealed a severe sensorimotor polyneuropathy with conduction velocities of 25 m/s - to normal. The conduction velocities in the upper 20's were seen in lower extremities with severe reduction of the corresponding compound muscle action potential amplitudes. She had a MPZ mutation with A-C transversion (nucleotide: 116, codon: 10, histidine-to-proline). Her sister has an identical mutation, with high arches, distal leg weakness, decreased vibration sensation in toes and ankle areflexia. Nerve conduction studies revealed a moderate-severe sensorimotor polyneuropathy with nerve conduction velocities of 36 m/s - to normal. Their mother had an abnormal gait and conduction velocities of 29-30 m/s. A third sister is clinically and genetically unaffected. One report has previously described four patients with this mutation with similar clinical and electrodiagnostic features. In patients tested for possible CMT, the frequency of MPZ His-Pro codon 10 substitutions was 0.11% (27 of 24,076 alleles).

Novel insertional presenilin 1 mutation causing Alzheimer disease with spastic paraparesis.

A four-generation pedigree exhibiting early-onset autosomal dominant Alzheimer disease (AD) with spastic paraplegia, dystonia, and dysarthria due to a novel 6-nucleotide insertional mutation in exon 3 of the presenilin 1 gene (PS1) is described. Serial examinations, PET scans, and autopsy revealed that the mutation in this highly conserved portion of PS1 causes an aggressive dementia that maintains the usual regional hierarchy of disease pathology while extending abnormalities into more widespread brain areas than typically seen in AD.

Clinical and genetic analysis of CMT1B in a Nigerian family.

We report a Nigerian family with a late-onset autosomal dominant neuropathy consistent with Charcot-Marie-Tooth disease. Electrophysiological examination of the index patient confirmed a severe demyelinating neuropathy with secondary axonal features. Sequence analysis of the myelin protein zero (MPZ) gene identified a C-to-G transversion at nucleotide position 234, resulting in a serine-to-tryptophan mutation in codon 78 (S78W) of the translated protein. The presence of this novel missense mutation suggests a diagnosis of Charcot-Marie-Tooth disease type 1B. Our study confirms the worldwide distribution of this disorder and extends the genetic spectrum of mutations in the MPZ gene.

Charcot-Marie-Tooth neuropathy: clinical phenotypes of four novel mutations in the MPZ and Cx 32 genes.

Charcot-Marie-Tooth Hereditary Neuropathy is a heterogeneous syndrome associated with mutations in several different genes including peripheral myelin protein 22, myelin P0, connexin 32, and early growth response 2. There is considerable variability in the phenotypic expression of this syndrome and the relationship of this variability to mutation genotypes requires extensive analysis. Here we describe the phenotypes and genotypes of four new mutations underlying the Charcot-Marie-Tooth syndrome and document segregation with disease. Four families with Charcot-Marie-Tooth were ascertained, examined, and evaluated electrophysiologically. Each family had peripheral blood DNA screened for mutations in myelin protein 22, myelin P0, and connexin 32. Two families were found with new mutations in the myelin P0 gene: S140T in the extracellular domain and K236del in the cytoplasmic domain. All families showed segregation of the mutations with the Charcot-Marie-Tooth phenotype as did a new family with the rare G163R mutation in the membrane domain. A 49-year-old man with the S140T mutation demonstrated conduction block on electrophysiological testing. A family with a novel S49P mutation in the connexin 32 gene had a neuropathy with very slow nerve conduction. These new mutations in the myelin P0 and connexin 32 genes help to clarify the pathophysiology of the clinical Charcot-Marie-Tooth syndrome. The S140T mutation in myelin P0 can be associated with conduction block and Charcot-Marie-Tooth should be part of the differential diagnosis of that phenomenon. Mutations in the cytoplasmic domain of myelin P0 can cause clinical neuropathy. The S49P mutation in the connexin 32 gene can produce aspects of a demyelinating type of X-linked hereditary neuropathy.

A founder mutation in presenilin 1 causing early-onset Alzheimer disease in unrelated Caribbean Hispanic families.

CONTEXT: Genetic determinants of Alzheimer disease (AD) have not been comprehensively examined in Caribbean Hispanics, a population in the United States in whom the frequency of AD is higher compared with non-Hispanic whites. OBJECTIVE: To identify variant alleles in genes related to familial early-onset AD among Caribbean Hispanics. DESIGN AND SETTING: Family-based case series conducted in 1998-2001 at an AD research center in New York, NY, and clinics in the Dominican Republic. PATIENTS: Among 206 Caribbean Hispanic families with 2 or more living members with AD who were identified, 19 (9.2%) had at least 1 individual with onset of AD before the age of 55 years. MAIN OUTCOME MEASURE: The entire coding region of the presenilin 1 gene and exons 16 and 17 of the amyloid precursor protein gene were sequenced in probands from the 19 families and their living relatives. RESULTS: A G-to-C nucleotide change resulting in a glycine-alanine amino acid substitution at codon 206 (Gly206Ala) in exon 7 of presenilin 1 was observed in 23 individuals from 8 (42%) of the 19 families. A Caribbean Hispanic individual with the Gly206Ala mutation and early-onset familial disease was also found by sequencing the corresponding genes of 319 unrelated individuals in New York City. The Gly206Ala mutation was not found in public genetic databases but was reported in 5 individuals from 4 Hispanic families with AD referred for genetic testing. None of the members of these families were related to one another, yet all carriers of the Gly206Ala mutation tested shared a variant allele at 2 nearby microsatellite polymorphisms, indicating a common ancestor. No mutations were found in the amyloid precursor protein gene. CONCLUSIONS: The Gly206Ala mutation was found in 8 of 19 unrelated Caribbean Hispanic families with early-onset familial AD. This genetic change may be a prevalent cause of early-onset familial AD in the Caribbean Hispanic population.

Fatal infantile X-linked neuropathy.

We report a pedigree with severe X-linked neuropathy that occurs in male infants and results in death, typically by 2 years of age. The proband of our report was weak with preserved mentation. He underwent extensive evaluation, which revealed abnormal nerve conduction studies, neurogenic changes on muscle biopsy, a decreased number of large myelinated fibers and rare onion bulb formations on nerve biopsy, negative gene testing for spinal muscular atrophy, CMT1a, and CMTX1 and a normal brain magnetic resonance image. The proband's mother, an obligate carrier, had normal nerve conduction studies. Male infants with a spinal muscular atrophy phenotype but normal genetic studies should be evaluated for this fatal X-linked neuropathy.

Assignment of electron transfer flavoprotein-ubiquinone oxidoreductase (ETF-QO) to human chromosome 4q33 by fluorescence in situ hybridization and somatic cell hybridization.

Electron transfer flavoprotein-ubiquinone oxidoreductase (ETF-QO) is a nuclear-encoded protein located in the inner mitochondrial membrane. Inherited defects of ETF-QO cause glutaric acidemia type II. We here describe the localization of the ETF-QO gene to human chromosome 4q33 by somatic cell hybridization and fluorescence in situ hybridization.

Demyelinating neuropathy in a patient with multiple sclerosis and genotypical HMSN-1.

Patients with multiple sclerosis (MS) may develop a peripheral neuropathy, sometimes attributed to nutritional deficiency. Other patients present with a demyelinating neuropathy which is presumed to be the result of an autoimmune process that affects both the central and peripheral nervous systems. We report a case of concurring MS and demyelinating neuropathy, without a positive family history, in whom genetic testing proved the neuropathy to be hereditary and not autoimmune. Hereditary neuropathy should be a consideration in sporadic cases of peripheral neuropathy and MS.

Relative stability of a minimal CTG repeat expansion in a large kindred with myotonic dystrophy.

The genetic basis for myotonic dystrophy (DM) is a CTG trinucleotide repeat expansion. The number of CTG repeats commonly increases in affected individuals of successive generations, in association with anticipation. We identified a large DM family in which multiple members had minimal CTG repeat expansions, and in which the number of CTG repeats remained in the minimally expanded range through at least three, and possibly four, generations. This relative stability of minimal CTG repeat expansions may help to maintain the DM mutation in the population.

Genotypic variations of type III collagen in patients with cerebral aneurysms.

It has been hypothesized that either qualitative or quantitative abnormalities in type III collagen may be involved in the pathogenesis of cerebral aneurysms. The current study investigated allele frequencies for the type III collagen gene in patients with cerebral aneurysms. A diallelic Ava II polymorphism defined the type III collagen gene. The smaller of the two alleles was found in 11 of 19 aneurysm patients (58%) versus two of 15 controls (13%) (p = .006). The overall frequency of this allele was 0.34 in aneurysm patients versus 0.10 in controls (p = .011). This significant difference in allele frequency suggests that genotypic variations in the type III collagen gene may be etiologically related to aneurysm formation.

Congenital adrenal hypoplasia, Duchenne muscular dystrophy, and glycerol kinase deficiency: importance of laboratory investigations in delineating a contiguous gene deletion syndrome.

We describe an infant with adrenal insufficiency who was subsequently diagnosed with Duchenne muscular dystrophy (DMD) and hyperglycerolemia due to glycerol kinase deficiency. Karyotyping showed a deletion on the short arm of the X chromosome (p21.1 to p22.1). Molecular mapping revealed that the deletion extended from the 3' end of the DMD gene to a site telomeric to the loci for X-linked congenital adrenal hypoplasia and glycerol kinase deficiency. These results are diagnostic for an Xp21 contiguous gene deletion syndrome--so named because the deletion manifests as a distinctive cluster of otherwise unrelated single-gene disorders in the same individual. The Xp21 syndrome should be considered in any infant with adrenal insufficiency. Measurement of serum triglycerides (without glycerol blanking) and creatine kinase activity are simple screening tests that may facilitate early diagnosis and appropriate genetic counseling about risks of recurrence in subsequent offspring.

Genetic analysis of Hispanic individuals with cystic fibrosis.

We have performed molecular genetic analyses of Hispanic individuals with cystic fibrosis (CF) in the southwestern United States. Of 129 CF chromosomes analyzed, only 46% (59/129) carry delta F508. The G542X mutation was found on 5% (7/129) of CF chromosomes. The 3849 + 10kbC-->T mutation, detected primarily in Ashkenazi Jews, was present on 2% (3/129). R1162X and R334W, mutations identified in Spain and Italy, each occurred on 1.6% (2/129) of CF chromosomes. W1282X and R553X were each detected once. G551D and N1303K were not found. Overall, screening for 22 or more mutations resulted in detection of only 58% of CF transmembrane conductance regulator gene mutations among Hispanic individuals. Analysis of KM19/XV2c haplotypes revealed an unusual distribution. Although the majority of delta F508 mutations are on chromosomes of B haplotypes, the other CF mutations are on A and C haplotypes at higher-than-expected frequencies. These genetic analyses demonstrate significant differences between Hispanic individuals with CF and those of the general North American population. Assessment of carrier/affected risk in Hispanic CF individuals cannot, therefore, be based on the mutation frequencies found through studies of the general population but must be adjusted to better reflect the genetic makeup of this ethnic group. Further studies are necessary to identify the causative mutation(s) in this population and to better delineate genotype/phenotype correlations. These will enable counselors to provide more accurate genetic counseling.

Effects of the sex of myotonic dystrophy patients on the unstable triplet repeat in their affected offspring.

The mutation responsible for myotonic dystrophy (DM) is an unstable expansion of the CTG repeat within the myotonin protein kinase gene. To examine whether the parental origin of the expanded repeat influences the repeat size in offspring, we studied 51 father-child and 59 mother-child pairs with DM. Small expansions in fathers resulted in larger size expansions in their offspring, while large paternal expansions resulted in less size change in their offspring. However, there was no correlation between maternal size expansion and size increase in offspring for either congenital or noncongenital DM. These data suggest that the sex of the affected parent influences the unstable expansion of the repeat in DM offspring. While some evidence suggests that DNA methylation status cannot explain this observation, the mechanism for differential maternal/paternal transmission expansion is currently unknown.

Negative-configuration electroretinogram in Oregon eye disease. Consistent phenotype in Xp21 deletion syndrome.

OBJECTIVE: To determine whether abnormal configurations on electroretinogram were a consistent finding in patients with Xp21 deletion and to characterize the associated ophthalmologic phenotype. DESIGN: Case series. SETTING: University hospitals and eye institutes. PATIENTS: Five patients with complex glycerol kinase deficiency (Duchenne-type or Becker's muscular dystrophy, glycerol kinase deficiency, and congenital adrenal hypoplasia) and demonstrated chromosomal deletions at Xp21. Control patients were matched by age. MAIN OUTCOME MEASURES: Clinical information was obtained from medical records. Complete ophthalmologic examinations were performed. Electroretinography was performed using a Ganzfeld technique and chloral hydrate sedation. RESULTS: We report the clinical features and abnormal configurations on electroretinograms of five patients with complex glycerol kinase deficiency, including follow-up studies on a previously described patient. The original patient had ocular hypopigmentation; four, strabismus; two, myopia; three, astigmatism; and one, symptomatic night blindness. All had negative configurations on scotopic electroretinograms showing a reduced-amplitude B wave in the dark-adapted state. CONCLUSIONS: Our original report suggested a diagnosis of Aland Island eye disease, which appears to be an incomplete form of congenital stationary night blindness. Linkage data place Aland Island eye disease and congenital stationary night blindness at Xp11, whereas our patients had deletions at Xp21. The phenotype reported here may represent the effects of a single gene defect or the compound effects of the Xp21 contiguous gene syndrome (complex glycerol kinase deficiency). The phenotype is referred to as Oregon eye disease.

Mental retardation locus in Xp21 chromosome microdeletion.

Xp21 microdeletion syndrome is associated with variable size Xp21 deletions that usually include the glycerol kinase locus. The clinical phenotypes we studied in this chromosome region include: Xpter - Aland Island eye disease (AIED) -adrenal hypoplasia (AH) -glycerol kinase (GKD) -Duchenne muscular dystrophy (DMD) -retinitis pigmentosa (RP) -ornithine transcarbamylase (OTC) -centromere. In a compilation of 18 individuals in 14 families with the AH, GKD, and DMD loci deleted, 17 were male and all were developmentally delayed. In contrast, we report mentally retarded female carriers in two Xp21 deletion syndrome families with DMD, GKD, and AH in affected males. In the first family with normal karyotypes, a submicroscopic deletion was associated with DMD in the retarded male and with retardation in carrier females. In the second family an X chromosome with a cytogenetically deleted Xp21 distal to the OTC and RP genes segregated in the affected male and retarded female carriers. DNA analysis at the DMD locus verified the cytogenetic findings. This report of mental retardation in otherwise asymptomatic female carriers of Xp21 deletion classifies one form of mental retardation in females.

Relationship of genotype to early pulmonary function in infants with cystic fibrosis identified through neonatal screening.

To determine whether pulmonary function in infants with asymptomatic cystic fibrosis is related to genotype, we studied 18 infants with cystic fibrosis identified through neonatal screening and 18 healthy control infants. Infants with cystic fibrosis (mean age, 2.0 months; range, 1.0 to 4.6 months) were identified from June 1990 to September 1991 through a statewide screening program based on elevated immunoreactive trypsinogen concentrations. Pulmonary function testing was done before and after inhalation of albuterol. There were no differences in pulmonary function between the cystic fibrosis group and the control infants (mean age, 2.7 months; range, 0.9 to 4.5 months). However, infants homozygous for the delta F508 deletion (n = 10) differed from infants with other genotypic variants of cystic fibrosis and control infants with respect to respiratory system resistance (79.4 +/- 11.5 vs 52.0 +/- 3.8 vs 55.5 +/- 5.0 cm H2O/L per second, respectively; p = 0.04) and specific conductance (0.15 +/- 0.02 vs 0.21 +/- 0.02 vs 0.21 +/- 0.02 cm H2O-1 sec-1, respectively; p = 0.02). Infants homozygous for the delta F508 deletion, but not other infants, responded to albuterol with a decrease in respiratory system resistance. We conclude that infants with asymptomatic cystic fibrosis homozygous for the delta F508 deletion have early evidence of airways obstruction and may need early respiratory treatment.

Mutation analysis of the cystic fibrosis transmembrane regulator gene in Native American populations of the southwest.

We report DNA and clinical analyses of cystic fibrosis (CF) in two previously unstudied, genetically isolated populations: Pueblo and Navajo Native Americans. Direct mutation analysis of six mutations of the CFTR gene--namely, delta F508, G542X, G551D, R553X, N1303K, and W1282X--was performed on PCR-amplified genomic DNA extracted from blood samples. Haplotype analyses with marker/enzyme pairs XV2c/TaqI and KM19/PstI were performed as well. Of the 12 affected individuals studied, no delta F508 mutation was detected; only one G542X mutation was found. None of the other mutations was detected. All affected individuals have either an AA, AC, or CC haplotype, except for the one carrying the G542X mutation, who has the haplotype AB. Clinically, six of the affected individuals examined exhibit growth deficiency, and five (all from the Zuni Pueblo) have a severe CF phenotype. Four of the six Zunis with CF are also microcephalic, a finding not previously noted in CF patients. Our DNA data have serious implications for risk assessment of CF carrier status for these people.