Clinical, electrophysiological and genetic characteristics of childhood hereditary polyneuropathies.

BACKGROUND: Hereditary polyneuropathies are heterogeneous group of diseases of the peripheral nervous system. In this study, we investigated the demographic, clinical, electrophysiological, and genetic characteristics of hereditary polyneuropathy patients diagnosed and followed up in our tertiary center clinic in Izmir, Turkey. METHODS: Patients who were diagnosed with hereditary polyneuropathies during nerve conduction studies in our center were evaluated retrospectively. RESULTS: In a total of 1484 nerve conduction studies, 207 patients were diagnosed with polyneuropathy. Ninety-nine of those patients were determined to have hereditary polyneuropathy, 52 of which were male and 47 were female. Sixty-nine patients with hereditary polyneuropathy were compatible with axonal and 30 were compatible with demyelinating polyneuropathy. Genetic analysis was performed in 69 patients, and 49 of those patients were genetically diagnosed, leading to a diagnosis rate of 71%. CONCLUSIONS: Advances in genetics have led to an increase in the heterogeneity of hereditary polyneuropathies, causing difficulties in the use of existing classifications. Although typical mutations expected in childhood-onset polyneuropathies are seen less frequently, polyneuropathies are frequently encountered as findings of complex, multisystemic diseases.

ATP13A2/PARK9 regulates endo-/lysosomal cargo sorting and proteostasis through a novel PI(3, 5)P2-mediated scaffolding function.

ATP13A2 (also called PARK9), is a transmembrane endo-/lysosomal-associated P5 type transport ATPase. Loss-of-function mutations in ATP13A2 result in the Kufor-Rakeb Syndrome (KRS), a form of autosomal Parkinson's disease (PD). In spite of a growing interest in ATP13A2, very little is known about its physiological role in stressed cells. Recent studies suggest that the N-terminal domain of ATP13A2 may hold key regulatory functions, but their nature remains incompletely understood. To this end, we generated a set of melanoma and neuroblastoma cell lines stably overexpressing wild-type (WT), catalytically inactive (D508N) and N-terminal mutants, or shRNA against ATP13A2. We found that under proteotoxic stress conditions, evoked by the proteasome inhibitor Bortezomib, endo-/lysosomal associated full-length ATP13A2 WT, catalytically-inactive or N-terminal fragment mutants, reduced the intracellular accumulation of ubiquitin-conjugated (Ub) proteins, independent of autophagic degradation. In contrast, ATP13A2 silencing increased the intracellular accumulation of Ub-proteins, a pattern also observed in patient-derived fibroblasts harbouring ATP13A2 loss-of function mutations. In treated cells, ATP13A2 evoked endocytic vesicle relocation and increased cargo export through nanovesicles. Expression of an ATP13A2 mutant abrogating PI(3,5)P2 binding or chemical inhibition of the PI(3,5)P2-generating enzyme PIKfyve, compromised vesicular trafficking/nanovesicles export and rescued intracellular accumulation of Ub-proteins in response to proteasomal inhibition. Hence, our study unravels a novel activity-independent scaffolding role of ATP13A2 in trafficking/export of intracellular cargo in response to proteotoxic stress.

Effects of Leucin-Enkephalins on Surface Characteristics and Morphology of Model Membranes Composed of Raft-Forming Lipids.

During the last decades opioid peptides, like enkephalins (Tyr-Gly-Gly-Phe-Met/Leu) are subject to extensive studies due to their antinociceptive action in organism. According to the membrane catalysis theory, in order to adopt a proper conformation for binding to their receptors, opioid peptides interact with the lipid phase of the membrane receptor surrounding. With this regard, the aim of the present work was to study the effects of synthetic leucine-enkephalin and leucine-enkephalinamide on surface characteristics and morphology of lipid monolayers, composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, sphingomyelin, and cholesterol alone and with their mixtures. The lipids were chosen to represent a model of a membrane raft, since it is known that G-protein-coupled receptors, including opioid receptors, are located preferably in membrane rafts. By using Langmuir's monolayer method, the change in surface pressure of the model membranes before and after the addition of the synthetic enkephalins was studied, and the compressional moduli of the lipids and lipid-peptides monolayers were determined. In addition, by Brewster angle microscopy, the surface morphology of the lipid monolayers alone and after the injection of both enkephalins was monitored. Our results showed that both leucine-enkephalins affected the lipid monolayers surface characteristics, and led to an increase in surface density of the mixed surface lipids/enkephalins films at loose lipid packing. This effect was more pronounced for the enkephalinamide, suggesting a different mechanism of interaction for the amidated enkephalin with the lipid phase, as compared to leucine-enkephalin.

Interaction of methionine-enkephalins with raft-forming lipids: monolayers and BAM experiments.

Enkephalins (Tyr-Gly-Gly-Phe-Met/Leu) are opioid peptides with proven antinociceptive action in organism. They interact with opioid receptors belonging to G-protein coupled receptor superfamily. It is known that these receptors are located preferably in membrane rafts composed mainly of sphingomyelin (Sm), cholesterol (Cho), and phosphatidylcholine. In the present work, using Langmuir's monolayer technique in combination with Wilhelmy's method for measuring the surface pressure, the interaction of synthetic methionine-enkephalin and its amidated derivative with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), Sm, and Cho, as well as with their double and triple mixtures, was studied. From the pressure/area isotherms measured, the compressional moduli of the lipids and lipid-peptide monolayers were determined. Our results showed that the addition of the synthetic enkephalins to the monolayers studied led to change in the lipid monolayers characteristics, which was more evident in enkephalinamide case. In addition, using Brewster angle microscopy (BAM), the surface morphology of the lipid monolayers, before and after the injection of both enkephalins, was determined. The BAM images showed an increase in surface density of the mixed surface lipids/enkephalins films, especially with double and triple component lipid mixtures. This effect was more pronounced for the enkephalinamide as well. These observations showed that there was an interaction between the peptides and the raft-forming lipids, which was stronger for the amidated peptide, suggesting a difference in folding of both enkephalins. Our research demonstrates the potential of lipid monolayers for elegant and simple membrane models to study lipid-peptide interactions at the plane of biomembranes.

Interaction of monogalactosyldiacylglycerol with cytochrome b6f complex in surface films.

The interaction of monogalactosyldiacylglycerol (MGDG) with cytochrome b(6)f complex (cyt b(6)f), a major component of the photosynthetic apparatus, was studied in Langmuir monolayers during compression/expansion cycling and at constant surface pressure mode. The surface pressure/area isotherms of the mixed films were analyzed in terms of surface compressional modulus and two-dimensional virial equation of state. The morphology and the surface potential of the monolayers were monitored by Brewster angle microscopy and vibrating plate sensor respectively. Our results suggested that there is a specific interaction between MGDG and cyt b(6)f which resulted in depletion of lipid molecules from the interface. The current work sheds light on the still unclear question how b(6)f complex gets in touch with the major compound of the thylakoid membranes, the non-charged lipid MGDG. The interaction occured even at very low sub-nanomolar concentration of the complex. This effect most probably could be attributed to hydrogen bonding between the galactose headgroup of the lipid and the protein moiety of cyt b(6)f.

Comparative study of the interaction of synthetic methionine-enkephalin and its amidated derivate with monolayers of zwitterionic and negatively charged phospholipids.

Using Langmuir's monolayer technique, the surface behavior and the interaction of the synthetic neuropeptide methionine-enkephalin (Met-enk) and its amidated derivate (Met-enk-NH(2)) with monolayers of the zwitterionic dimyristoylphosphatidylcholine (DMPC) and the negatively charged dimyristoylphosphatidylglycerol (DMPG) were studied. The surface tension (γ, mN/m) of DMPG and DMPC monolayers as a function of time (after injection of the peptide under the interface) was detected. The decrease in γ values showed that there was a strong penetration effect of both types of Met-enk molecules into the monolayers, being significantly stronger for the amidated derivate, Met-enk-NH(2). We suggest that the interaction between the neuropeptides and DMPC was predominantly determined by peptides amphiphilicity, while the electrostatic forces play significant role for the insertion of the cationic Met-enk-NH(2) in DMPG monolayers, especially at high packing densities. Our results demonstrate the potential of lipid monolayers formed in Langmuir's trough to be successfully used as an elegant and simple membrane models to study lipid-peptide interactions at the air/water interface.

[Study of the lung surfactant maturity by biochemical and biophysical analyses of gasral aspirates from newborn infants].

The aim of the present study was to estimate the lung surfactant maturity by analyses of gastral aspirates (GA) from prematurely born and full-term infants. A biochemical analysis of the protein and lipid content in GA from the children groups tested was made. By thin-layer chromatography the individual phospholipids components in GA samples from prematurely born and full-term children were detected. In addition, by using the pending drop method the surface characteristics (equilibrium, maximal and minimal surface tension values) were determined. Our results showed an increase in the phospholipid and the protein concentrations in GA during pregnancy progress as well as significant differences in the individual phospholipids profile of the aspirates from prematurely born and full-term children. In case of surface characteristics a highest difference was observed for the minimal surface tension values (gammamin, m/Nm); while in the full-term children a lower surface tension was determined, in the prematurely born children significant higher values were reached, which define gammamin as the most informative from the parameters studied. Our results could find application into the clinical practice for fast surfactant maturity diagnostics in prematurely born children regarding lifesaving therapy with exogenous surfactants administration.

Investigations to the synthesis of n.c.a. [18F]FClO3 as electrophilic fluorinating agent.

An approach to synthesize the electrophilic fluorinating agent no-carrier-added (n.c.a.) [18F]perchloryl fluoride ([18F]FClO3) in superacidic media in the presence of KClO4 or anhydrous perchloric acid starting from [18F]fluoride was demonstrated in this study. However, the radiochemical yields were low (1-6%) and poorly reproducible. Fluorosulphonic acid proved to be an essential intermediate as revealed by non-radioactive experiments. A key problem in the preparation of [18F]FClO3 is the assumed kinetic inhibition due to the unfavourable stoichiometric ratio of the ClO4 moiety to [18F]HSO3F.

Pontocerebellar hypoplasia type 1 for the neuropediatrician: Genotype-phenotype correlations and diagnostic guidelines based on new cases and overview of the literature.

Pontocerebellar hypoplasia type 1 (PCH1) is a major cause of non-5q spinal muscular atrophy (SMA). We screened 128 SMN1-negative SMA patients from Bulgaria for a frequent mutation -p.G31A in EXOSC3, and performed a literature review of all genetically verified PCH1 cases. Homozygous p.G31A/EXOSC3 mutation was identified in 14 Roma patients, representing three fourths of all our SMN1-negative Roma SMA cases. The phenotype of the p.G31A/EXOSC3 homozygotes was compared to the clinical presentation of all reported to date genetically verified PCH1 cases. Signs of antenatal onset of disease present at birth were common in all PCH1 sub-types except in the homozygous p.D132A/EXOSC3 patients. The PCH1sub-types with early death (between ages 1 day and 17 months), seen in patients with p.G31A/EXOSC3 or SLC25A46 mutations have a SMA type 1-like clinical presentation but with global developmental delay, visual and hearing impairment, with or without microcephaly, nystagmus and optic atrophy. Mutations with milder presentation (homozygous p.D132A/EXOSC3 or VRK1) may display additionally signs of upper motor neuron impairment, dystonia or ataxia and die at age between 5 and 18 years. Other EXOSC3 mutations and EXOSC8 cases are intermediate - SMA type 1-like presentation, spasticity (mostly in EXOSC8) and death between 3 months and 5 years. There is no correlation between neurological onset and duration of life. We add marble-like skin and congenital laryngeal stridor as features of PCH1. We show that imaging signs of cerebellar and pontine hypoplasia may be missing early in infancy. EMG signs of anterior horn neuronopathy may be missing in PCH1 patients with SLC25A46 mutations. Thus, there is considerable phenotypic variability in PCH1, with some cases being more SMA-like, than PCH-like. Detailed clinical evaluation and ethnicity background may guide genetic testing and subsequent genetic counseling.

Neuroprotection in glaucoma--delusion, reality or hope?

The global definition of glaucoma considers it as an optic neuropathy with multifactor etiology, which affects the optic nerve head (ONH), provoking visual field loss and permanent impairment of visual function. Bearing in mind the fact that the exact pathogenic mechanism is still not completely established, glaucoma treatment strategies so far are based upon the identification of glaucoma risk factors. Among them, only elevated intraocular pressure (IOP) could undergo therapeutic treatment. However, in spite of the adequate therapy and IOP lowering, very often the disease is still progressing, leading to definite visual loss and permanent blindness. This especially refers to "normal tension glaucoma". Over the last decade, there has been significant scientific research on new strategies for the delay or prevention of retinal ganglion cell loss (RGC), which is the basic pathophysiological event that initiates the cascade of processes leading to optic atrophy. Therefore, a great deal of expectation has been put on the concept of what is known as "neuroprotection". This includes the development of treatment strategies (pharmacological, immunological, genetic) that would be capable of preventing apoptotic death of retinal ganglion cells. The concept of neuroprotection is based upon increasing evidence that glaucoma degeneration is analogous with other neurodegenerative diseases of the central nervous system suggesting a strong relation between the basic cellular processes in glaucoma and Alzheimer's disease, for example. It is considered that retinal ganglion cell death goes through two phases--primary injury responsible for initiation of damage that is followed by slower secondary degeneration related to a harmful environment surrounding the degenerated cells. Neuroprotection in glaucoma refers to any intervention that is aimed at prevention of the optic nerve head injury and ganglion cells death. Pharmacological intervention is aimed at neutralizing some of the effects of the nerve-derived toxic factors by increasing the ability of the remaining neurons to cope with stressful conditions. On the other hand, immunological reaction stimulates the body's repair mechanisms so as to hinder the toxic effects of various chemical agents generated during pathological events.

Dominant GDAP1 mutations cause predominantly mild CMT phenotypes.

OBJECTIVE: Ganglioside-induced differentiation associated-protein 1 (GDAP1) mutations are commonly associated with autosomal recessive Charcot-Marie-Tooth (ARCMT) neuropathy; however, in rare instances, they also lead to autosomal dominant Charcot-Marie-Tooth (ADCMT). We aimed to investigate the frequency of disease-causing heterozygous GDAP1 mutations in ADCMT and their associated phenotype. METHODS: We performed mutation analysis in a large cohort of ADCMT patients by means of bidirectional sequencing of coding regions and exon-intron boundaries of GDAP1. Intragenic GDAP1 deletions were excluded using an allele quantification assay. We confirmed the pathogenic character of one sequence variant by in vitro experiments assaying mitochondrial morphology and function. RESULTS: In 8 Charcot-Marie-Tooth disease (CMT) families we identified 4 pathogenic heterozygous GDAP1 mutations, 3 of which are novel. Three of the mutations displayed reduced disease penetrance. Disease onset in the affected individuals was variable, ranging from early childhood to adulthood. Disease progression was slow in most patients and overall severity milder than typically seen in autosomal recessive GDAP1 mutations. Electrophysiologic changes are heterogeneous but compatible with axonal neuropathy in the majority of patients. CONCLUSIONS: With this study, we broaden the phenotypic and genetic spectrum of autosomal dominant GDAP1-associated neuropathies. We show that patients with dominant GDAP1 mutations may display clear axonal CMT, but may also have only minimal clinical and electrophysiologic abnormalities. We demonstrate that cell-based functional assays can be reliably used to test the pathogenicity of unknown variants. We discuss the implications of phenotypic variability and the reduced penetrance of autosomal dominant GDAP1 mutations for CMT diagnostic testing and counseling.

Distal myopathy with upper limb predominance caused by filamin C haploinsufficiency.

OBJECTIVE: In this study, we investigated the detailed clinical findings and underlying genetic defect in 3 presumably related Bulgarian families displaying dominantly transmitted adult onset distal myopathy with upper limb predominance. METHODS: We performed neurologic, electrophysiologic, radiologic, and histopathologic analyses of 13 patients and 13 at-risk but asymptomatic individuals from 3 generations. Genome-wide parametric linkage analysis was followed by bidirectional sequencing of the filamin C (FLNC) gene. We characterized the identified nonsense mutation at cDNA and protein level. RESULTS: Based on clinical findings, no known myopathy subtype was implicated in our distal myopathy patients. Light microscopic analysis of affected muscle tissue showed no specific hallmarks; however, the electron microscopy revealed changes compatible with myofibrillar myopathy. Linkage studies delineated a 9.76 Mb region on chromosome 7q22.1-q35 containing filamin C (FLNC), a gene previously associated with myofibrillar myopathy. Mutation analysis revealed a novel c.5160delC frameshift deletion in all patients of the 3 families. The mutation results in a premature stop codon (p.Phe1720LeufsX63) that triggers nonsense-mediated mRNA decay. FLNC transcript levels were reduced in muscle and lymphoblast cells from affected subjects and partial loss of FLNC in muscle tissue was confirmed by protein analysis. CONCLUSIONS: The FLNC mutation that we identified is distinct in terms of the associated phenotype, muscle morphology, and underlying molecular mechanism, thus extending the currently recognized clinical and genetic spectrum of filaminopathies. We conclude that filamin C is a dosage-sensitive gene and that FLNC haploinsufficiency can cause a specific type of myopathy in humans.

Properties of alkyl-phosphatidylcholine monolayers in the presence of surface-active three-block copolymers.

The interaction of three-block copolymers (poloxamers) with dimyristoyl-phosphatidylcholine (DMPC) and dipalmitoylphosphatidylcholine (DPPC) was investigated in monolayer experiments. The poloxamers selected were BASF PLURONICS F-68, F-88 and F-98. All of them are water-soluble and possess two hydrophilic polyoxyethylene and one hydrophobic polyoxypropylene moiety but differ in molecular weight. These substances and their interfacial behaviour are interesting for the development of targeted drug delivery systems. Monolayer tensiometry revealed the degree of poloxamer penetration in PC monolayers and the changes in monolayer compression/expansion behaviour. Two different experimental protocols were used to determine the surface pressures (pi) and areas (A) at "squeeze-out" (compression) and "insertion" (expansion) of the soluble component in the surface layer. The two protocols yielded differences in the "squeeze-out" and "insertion" parameters of the DMPC (DPPC)/Poloxamer systems. The differences disappear when comparing the product piA (2-D - "mechanical work") for the various combinations of lipids and poloxamers. In all cases (piA)(out)>(piA)(in). This approach reveals a possibility for adequate comparison of monolayer compression/expansion isotherms made by different experimental protocols.

Interactions of Meibomian gland secretion with polar lipids in Langmuir monolayers.

The surface interactions of Meibomian gland secretion (MGS) with polar lipid (PL), Egg Sphingomyelin (SM) or Dipalmitoylphosphatidylcholine (DPPC), are studied in mixed pseudo-binary films formed at the air/water interface of Langmuir surface balance. The behavior of the mixed films during slow quasi-equilibrium compression and during fast dynamic compression-decompression is registered by measurements of surface pressure and surface potential, and by monitoring film morphology with Brewster Angle Microscopy (BAM). Quasi-equilibrium compression isotherms are used to calculate the excess Gibbs and Helmholtz energy of mixing between MGS and PLs and thus to evaluate the interactions between the lipid compounds at the interface. The effects of PLs on the mixed film's elastic moduli of area compressibility, morphology and capability to attain high surface pressures are also examined. PLs interact with MGS with different strength and in different manner: MGS-SM interaction is weak and might lead to interfacial disaggregation of the thick meibium domains when SM is in excess, while MGS-DPPC interaction is strong and results in the formation of thick lipid aggregates. Both PLs increase the mixed films reciprocal compressibility and capability to achieve higher surface pressures. The results demonstrate that in vitro studies of the surface interactions between MGS and PLs might be beneficial in the selection of PLs for artificial tear formulations and for examination on molecular scale of the possible role of PLs at the ocular surface.

Four generations of epilepsy caused by an inherited microdeletion of the SCN1A gene.

OBJECTIVES: The aim of this study was to determine the genetic defect in a 4-generational family with an epileptic disorder characterized by febrile and afebrile polymorphic seizures and mild to severe mental retardation by means of analyzing the neuronal voltage-gated sodium channel alpha-subunit gene SCN1A for mutations. METHODS: A Bulgarian family was ascertained and clinically assessed, followed by mutation analysis of the SCN1A gene using direct sequencing to detect point mutations and multiplex amplicon quantification to identify copy number variations. RESULTS: A microdeletion encompassing the entire SCN1A gene segregating with all affected members was identified in this family. Additional analysis showed that the unaffected father of the proband is mosaic for the deletion. So far, SCN1A deletions, predicted to lead to haploinsufficiency, are exclusively identified in isolated patients with Dravet or contiguous gene syndromes. Because of the severe phenotype, SCN1A deletion carriers are usually not able to live independently and start a family, and hence do not transmit the disease. CONCLUSIONS: We report an inherited SCN1A gene deletion not exclusively associated with Dravet syndrome. Moreover, our results demonstrate that SCN1A haploinsufficiency can cause a significant intrafamilial clinical variability including moderately affected to syndromal patients. The involvement of multiple genetic and environmental factors could be the basis of this difference in phenotype severity.

Clinical spectrum of early-onset epileptic encephalopathies associated with STXBP1 mutations.

OBJECTIVES: Heterozygous mutations in STXBP1, encoding the syntaxin binding protein 1, have recently been identified in Ohtahara syndrome, an epileptic encephalopathy with very early onset. In order to explore the phenotypic spectrum associated with STXBP1 mutations, we analyzed a cohort of patients with unexplained early-onset epileptic encephalopathies. METHODS: We collected and clinically characterized 106 patients with early-onset epileptic encephalopathies. Mutation analysis of the STXBP1 gene was done using sequence analysis of the exon and intron-exon boundaries and multiplex amplification quantification to detect copy number variations. RESULTS: We identified 4 truncating mutations and 2 microdeletions partially affecting STXBP1 in 6 of the 106 patients. All mutations are predicted to abolish STXBP1 function and 5 mutations were proven to occur de novo. None of the mutation-carrying patients had Ohtahara syndrome. One patient was diagnosed with West syndrome at disease onset, while the initial phenotype of 5 further patients did not fit into a specific recognized epilepsy syndrome. Three of these patients later evolved to West syndrome. All patients had severe to profound mental retardation, and ataxia or dyskinetic movements were present in 5 patients. CONCLUSION: This study shows that mutations in STXBP1 are not limited to patients with Ohtahara syndrome, but are also present in 10% (5/49) of patients with an early-onset epileptic encephalopathy that does not fit into either Ohtahara or West syndrome and rarely in typical West syndrome. STXBP1 mutational analysis should be considered in the diagnostic evaluation of this challenging group of patients.

Mutations in SACS cause atypical and late-onset forms of ARSACS.

BACKGROUND: Autosomal recessive spastic ataxia of Charlevoix-Saguenay (ARSACS) is a complex neurodegenerative disorder caused by mutations in SACS. The phenotype consists of a childhood-onset triad of cerebellar ataxia, peripheral neuropathy, and pyramidal tract signs. OBJECTIVE: To provide more insight into the prevalence of SACS mutations and the variability of the associated phenotype. METHODS: Mutation screening of SACS by direct sequencing and multiplex amplicon quantification for detection of intragenic copy number variations in a cohort of 85 index patients with phenotypes suggestive for ARSACS. Additional short tandem repeat (STR) marker analysis was performed for haplotype sharing. RESULTS: In 11 families,18 new SACS mutations were found (12.9% of total cohort). Five patients displayed onset ages in adulthood, a feature not known to be associated with ARSACS. The remaining index patients displayed a classic early onset phenotype. Initial phenotypic presentation was atypical in several patients, obscuring the clinical diagnosis. A founder mutation in SACS was identified in 3 Belgian families. In one isolated patient, an intragenic SACS deletion of exons 3-5 was detected. Partial SACS deletions were not previously described. CONCLUSIONS: In this study, we enlarge the ARSACS phenotype and the underlying genetic spectrum of SACS mutations. Patients with ARSACS are more common than previously known and risk underdiagnosis due to late onset age and unusual presentation.

Spastin gene mutations in Bulgarian patients with hereditary spastic paraplegia.

Hereditary spastic paraplegia (HSP) is an extremely heterogeneous group of neurodegenerative disorders affecting the longest axons in the central nervous system. The most common genetic form accounting for about 40% of the autosomal-dominant HSP (ADHSP) cases is spastin gene, SPG4. We performed mutation screening of the spastin gene on 36 unrelated HSP patients from three different ethnic groups (Bulgarian, Turks and Gypsies) and found four new mutations and one already reported. The phenotype-genotype correlations in Bulgarian SPG4 patients showed a great difference in the age at disease onset between patients with missense mutations and those harboring deletions and splice-site mutations. Our study is the first to present corroborative clinical data in favor of the general hypothesis that the clinical course of the disease is related to the type of the spastin mutation. The clinical and genealogical findings in Bulgarian SPG4 patients suggest that a positive family history for inheritance as an autosomal-dominant trait is a strong indication for spastin mutation screening.

Double mutant alleles: are they rare?

The presence of two different mutations carried by the same CF allele has been demonstrated in four out of 44 Bulgarian CF patients during a systematic search of the entire coding sequence of the CFTR gene. Two of the double mutant alleles include one nonsense and one missense mutation and although the nonsense mutation can be considered to be the main defect, the amino acid substitutions are good candidates for disease-causing mutations as well. One double mutant carries two missense mutations whose contribution to the CF phenotype is difficult to evaluate. The findings suggest that double mutant alleles may be more common than expected and could account for some of the problems in phenotype-genotype correlations. Such alleles may have important implications for molecular diagnosis and genetic counselling.

Deletion analysis of Bulgarian SMA families.

All three types of autosomal recessive spinal muscular atrophy map to chromosome region 5q13. Recent reports suggest that they are associated with deletions of two adjacent genes: SMN and NAIP. Here we report the first deletion analysis of Bulgarian SMA families. Homozygous deletion of exons 7 and 8 of the SMN gene were found in 85% of our patients, but the NAIP gene (exons 5 and 6) was deleted in only 26% of patients. To our knowledge, these frequencies are some of the lowest reported so far. The NAIP gene was deleted predominantly in severely affected patients (type I), while in the group with milder types SMA only deletions of the SMN gene were detected. Our phenotype-genotype correlation study confirmed that larger deletions are associated with more severe clinical course. The Bulgarian data support the thesis that the telomeric SMN gene could play a major role in determining SMA, while the NAIP or the centromeric SMN copy have a modifying effect on the phenotype.