F. Muntoni

Low doses of ethanol activate dopaminergic neurons in the ventral tegmental area.

In unanesthetized rats the intravenous administration of low doses of ethanol (0.125-0.5 g/kg) produced a dose-dependent increase (30-80%) in the firing rate of dopaminergic (DA) neurons in the Ventral Tegmental Area (VTA). In agreement with previous observations, a dose range between 0.5 and 2 g/mg of ethanol was needed to produce comparable stimulant responses in DA neurons of the Substantia Nigra Pars Compacta. However, in anesthetized rats, doses of ethanol up to 1 g/kg failed to activate VTA-DA neurons. The high sensitivity of VTA-DA neurons to ethanol activation suggests that they might be involved in the reinforcing properties of the drug.

Clinical and molecular genetic spectrum of autosomal dominant Emery‐Dreifuss muscular dystrophy due to mutations of the lamin A/C gene

Emery‐Dreifuss muscular dystrophy (EDMD) is characterized by early contractures of the elbows and Achilles tendons, slowly progressive muscle wasting and weakness, and life‐threatening cardiomyopathy with conduction blocks. We recently identified LMNA encoding two nuclear envelope proteins, lamins A and C, to be implicated in the autosomal dominant form of EDMD. Here, we report on the variability of the phenotype and spectrum of LMNA mutations in 53 autosomal dominant EDMD patients (36 members of 6 families and 17 sporadic cases). Twelve of the 53 patients showed cardiac involvement exclusively, although the remaining 41 all showed muscle weakness and contractures. We were able to identify a common phenotype among the patients with skeletal muscle involvement, consisting of humeroperoneal wasting and weakness, scapular winging, rigidity of the spine, and elbow and Achilles tendon contractures. The disease course was generally slow, but we observed either a milder phenotype characterized by late onset and a mild degree of weakness and contractures or a more severe phenotype with early presentation and a rapidly progressive course in a few cases. Mutation analysis identified 18 mutations in LMNA (ie, 1 nonsense mutation, 2 deletions of a codon, and 15 missense mutations). All the mutations were distributed between exons 1 and 9 in the region of LMNA that is common to lamins A and C. LMNA mutations arose de novo in 76% of the cases; 2 of these de novo mutations were typical hot spots, and 2 others were identified in 2 unrelated cases. There was no clear correlation between the phenotype and type or localization of the mutations within the gene. Moreover, a marked inter‐ and intra‐familial variability in the clinical expression of LMNA mutations exists, ranging from patients expressing the full clinical picture of EDMD to those characterized only by cardiac involvement, which points toward a significant role of possible modifier genes in the course of this disease. In conclusion, the high proportion of de novo mutations together with the large spectrum of both LMNA mutations and the expression of the disease should now prompt screening for LMNA in familial and sporadic cases of both EDMD and dilated cardiomyopathy associated with conduction system disease. Ann Neurol 2000;48:170–180

Charcot-Marie-Tooth disease type 2 associated with mutation of the myelin protein zero gene

Charcot-Marie-Tooth disease (CMT), or hereditary motor and sensory neuropathy (HMSN), is a clinically and genetically heterogeneous condition. Mutations of the myelin protein zero (MPZ) gene have been associated with CMT1B, Déjerine-Sottas disease, and congenital hypomyelination, which are inherited demyelinating neuropathies characterized by different clinical severity. HMSN type II (HMSN II) or CMT2, the axonal form of CMT, is genetically heterogeneous. Linkage to 1p35-p36 (CMT2A), 3q(CMT2B), and 7p (CMT2D) chromosomes has been reported in the disease; however, most HMSN II families do not link to any of the reported loci. In a large HMSN II Sardinian family, we found a missense mutation in the chromosome 1q MPZ gene. This Ser44Phe mutation was located in exon 2 and was present in the heterozygous state in all affected individuals. This is the first example of an HMSN II family showing an MPZ point mutation. The MPZ gene Ser 44Phe mutation found in the HMSN II family presented in this study suggests that genetic analysis of HMSN II families should also include the MPZ gene, previously not considered to be involved in the axonal form of HMSN.

The phenotype of limb-girdle muscular dystrophy type 2I

Background: Mutations in the fukutin-related protein gene FKRP cause limb-girdle muscular dystrophy (LGMD2I) as well as a form of congenital muscular dystrophy (MDC1C). Objective: To define the phenotype in LGMD2I. Methods: The authors assessed 16 patients from 14 families with FKRP gene mutations and LGMD and collected the results of mutation analysis, protein studies, and respiratory and cardiac investigations. Results: Thirteen patients, most with adult presentation, were homozygous for the common C826A mutation in FKRP. The three other cases were compound heterozygotes for C826A and two of them presented in childhood, with more progressive disease. The pattern of muscle involvement, frequently including calf hypertrophy, was similar to dystrophinopathy. Complications in patients with LGMD2I were common and sometimes out of proportion to the skeletal muscle involvement. Six patients had cardiac involvement, and 10 had respiratory impairment: five required nocturnal respiratory support. All patients had serum creatine kinase at least 5 to 70 times normal. The most consistent protein abnormality found on muscle biopsy was a reduction of laminin α2 immunolabeling, either on muscle sections or immunoblotting alone. Conclusions: LGMD2I due to FKRP mutations appears to be a relatively common cause of LGMD, with respiratory and cardiac failure as prominent complications.

Multiple Sclerosis in Sardinia Is Associated and in Linkage Disequilibrium with HLA-DR3 and -DR4 Alleles

The preponderance of genetic factors in attempts to account for susceptibility to multiple sclerosis (MS), a common inflammatory and demyelinating disease of young adults, has recently been demonstrated (Ebers et al . 1995). The inheritance of MS appears to be complex and is believed to involve several genes (Ebers et al . 1996; The Multiple Sclerosis Genetics Group 1996; Sawcer et al . 1996). Methodological approaches to the study of genes conferring susceptibility to MS include association studies, which measure the frequency of a specific allele in affected and healthy populations, and linkage studies, which trace the inheritance of a gene from parents and correlate these genes to disease susceptibility.

A MERRF/MELAS Overlap Syndrome Associated with a New Point Mutation in the Mitochondrial DNA tRNA^Lys Gene

Several members of a three-generation kindred from Sardinia were affected by a maternally inherited syndrome characterized by features of both myoclonus epilepsy with ragged-red fibers (MERRF) and mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes (MELAS). Clinically, symptoms such as myoclonus epilepsy, neural deafness and ataxia were variably associated with stroke-like episodes and/or migrainous attacks. Morphologically, numerous ME-LAS-associated SDH-stained vessels were observed in muscle biopsies, either alone or in combination with ragged-red fibers, the morphological hallmark of MERRF. Sequence analysis of the mtDNA tRNA genes revealed the presence of a single, heteroplasmic T → C transition at nt 8356, in the region of the tRNALys gene corrsponding to the T-Ψ-C stem. The T → C(8356) transition was exclusively found in the maternal lineage of our family, and the relative amount of the mutant mtDNA species in muscle was correlated with the severity of the clinical presentation. Therefore, we propose that the T → C(8356) transition is responsible for the mitochondrial encephalomyopathy found in our family, and must be added to the expanding list of the pathogenetically relevant mutations of human mtDNA.

Sardinian multiple sclerosis is associated with HLA‐DR4 A serologic and molecular analysis

HLA haplotypes in 45 unrelated Sardinian multiple sclerosis patients and in six multiplex families were defined, using both serologic and restriction fragment length polymorphism (RFLP) analysis. In unrelated MS patients, we found an association with HLA-DR4 (p < 0.01, relative risk = 2.5) and DQw3 (p < 0.04, relative risk = 2.2). Using a β-DR cDNA probe, we observed no variation of the DR4 RFLP profile in sporadic or related MS patients compared with DR4-specific pattern in controls. Using a β-DQ cDNA probe, we identified two DQw3 patterns (DQw3.1 and DQw3.2) with similar frequency in patients and in controls. No specific RFLPs were observed in association with different disease courses. The frequency of haplotype sharing in affected members of multiplex families was not different from that expected by chance. This study shows that Sardinian MS patients carry predominantly the HLA-DR4 allele, in contrast to the DR2 prevalence reported in Caucasian populations. The lack of association with HLA haplotypes in affected members of multiplex families may indicate that genetic factors outside the HLA system play a substantial role in families with MS.

FKRP gene mutations cause congenital muscular dystrophy, mental retardation, and cerebellar cysts

Background: Congenital muscular dystrophies (CMD) are autosomal recessive disorders that present within the first 6 months of life with hypotonia and a dystrophic muscle biopsy. CNS involvement is present in some forms. The fukutin-related protein gene (FKRP) is mutated in a severe form of CMD (MDC1C) and a milder limb girdle dystrophy (LGMD2I). Both forms have secondary deficiencies of laminin α2 and α-dystroglycan immunostaining. Structural brain involvement has not been observed in patients with FKRP gene mutations. Methods: The authors studied two unrelated patients who had a pattern of muscle involvement identical to MDC1C, mental retardation, and cerebellar cysts on cranial MRI. The FKRP gene was analyzed along with the skeletal muscle expression of laminin α2 and α-dystroglycan. Results: The muscle biopsy of both patients showed severe dystrophic findings, a reduction in laminin α2, and profound depletion of α-dystroglycan. Both patients had homozygous FKRP gene mutations not previously reported (C663A [Ser221Arg] and C981A [Pro315Thr]). Conclusions: Mutations within the FKRP gene can result in CMD associated with mental retardation and cerebellar cysts. This adds structural brain defects to the already wide spectrum of abnormalities caused by FKRP mutations. The severe depletion of α-dystroglycan expression suggests that FKRP is involved in the processing of α-dystroglycan.

Combinations of specific DRB1, DQA1, DQB1 haplotypes are associated with insulin-dependent diabetes mellitus in sardinia

The Sardinian population has an extremely high incidence of IDDM (30.2 of 100.000 in the age group of 0-14 years). This study reports the molecular characterization of HLA class II genes in 120 IDDM sporadic patients and 89 healthy subjects of Sardinian origin. Compared with other Caucasians, both Sardinian patients and controls had an unusual distribution of haplotypes and genotypes. In particular, there was a high gene frequency of the DRB1*0301, DQA1*0501, DQB1*0201 susceptibility haplotype both in patients (0.58) and controls (0.23) while a reduction of the DRB1*1501, DQA1*0102, DQB1*0602 protective haplotype (0.03) was observed in the healthy population. This distribution may partially explain the high incidence of IDDM reported in Sardinia. The analysis of the DQ beta 57 and DQ alpha 52 residues showed that the absence of Asp 57 and the presence of Arg 52 were associated with IDDM in a dose-response manner. On the other hand, we found that (a) a very similar distribution of these residues was found when comparing Sardinians with another healthy Caucasian population from the same latitude but with a lower rate of IDDM incidence; (b) several genotypes encoding the identical DQ alpha 52/DQ beta 57 phenotype carried very different relative risks; and (c) the DRB1*0403, DQA1*0301, DQB1*0304 haplotype (DQ beta 57 Asp-neg and DQ alpha 52 Arg-pos) was found in 40% of the DR4-positive controls but not in patients (p = 0.00034), while the DRB1*0405, DQA1*0301, and DQB1*0302 haplotype carrying the same residues at the same positions was found in 70% of the DR4-positive patients and in only one control (p = 0.00003). These findings suggest that IDDM susceptibility cannot be completely explained by the model in which only DQ alpha 52 and DQ beta 57 residues are taken into account.

Stress-induced insomnia: opioid-dopamine interactions

REM sleep deprivation induced by means of the platform technique (72 h) was followed by a period of latency to sleep characterized by a marked excitement in rats. The administration of naloxone at the end of the REM deprivation period reduced this latency to sleep while morphine, beta-endorphin and DADLE prolonged it. The dopamine D1 receptor antagonist SCH 23390 was extremely potent (0.003 mg/kg) to reduce the latency to sleep and the excitement while the D1 agonist SKF 38393 induced an opposite effect. The dopamine D2 receptor antagonist L-sulpiride was inactive up to a dose of 25 mg/kg. These data suggest that hyperactivity of the opioid and dopamine systems (specifically mediated through D1 receptors) is involved in such behaviour.