Pieter A. Bolhuis

De-novo mutation in hereditary motor and sensory neuropathy type I

Isolated cases of hereditary motor and sensory neuropathy type I (HMSN I, Charcot-Marie-Tooth disease type 1) have been thought to be most frequently autosomal recessive. We have found that a recently discovered duplication in chromosome 17, responsible for most cases of autosomal dominant HMSN I, is present as a de-novo mutation in 9 out of 10 sporadic patients. This finding has important implications for genetic counselling of isolated patients with HMSN I.

Two divergent types of nerve pathology in patients with different P0 mutations in Charcot-Marie-Tooth disease

In seven unrelated patients with a demyelinating motor and sensory neuropathy, we found mutations in exons 2 and 3 of the P sub 0 gene.Morphologic examination of sural nerve biopsy specimens showed a demyelinating process with onion bulb formation in all cases. In four patients, ultrastructural examination demonstrated uncompacted myelin in 23 to 68% of the myelinated fibers, which is in agreement with the widely accepted function of P0 as a homophilic adhesion molecule. Three patients showed normal compact myelin, but morphology was dominated by the abundant occurrence of focally folded myelin. The two divergent pathologic phenotypes exemplify that some mutations act differently on P0 protein formation or function than others, which is probably determined by site and nature of the mutation in the P0 gene. NEUROLOGY 1996;47: 761-765

Rapid shift in genotype of human mitochondrial DNA in a family with Leber's hereditary optic neuropathy

Mitochondrial DNA isolated from white blood cells was investigated in families suffering from Lebers hereditary optic neuropathy. A recently described mutation at nucleotide position 11778 was present in 5 out of 12 families and heteroplasmic mitochondrial DNA was observed in 2 of these 5 families. A rapid shift in genotype was found in one of the families with heteroplasmy: the grandmother had 60 percent mitochondrial DNA mutated at nucleotide position 11778, the mother 55 percent, and the two sons at least 95 percent. These data indicate that the number of mitochondrial DNA molecules transmitted to the progeny passes a developmental bottleneck, as previously proposed to occur in bovine oogenesis.

Differentiation and proliferation of respiration-deficient human myoblasts

Replication and transcription of mitochondrial DNA were impaired in dividing human myoblasts exposed to ethidium bromide. MtDNA content decreased linearly per cell division and mitochondrial transcript levels declined rapidly, resulting in respiration-deficiency of the myoblasts. Despite the absence of functional mitochondria the cells remained able to proliferate when grown under specific culture conditions. However, the formation of myotubes was severely impaired in respiration-deficient myoblasts. We conclude that differentiation of myoblasts into myotubes is more dependent on mitochondrial function than proliferation of myoblasts.

Riboflavin‐responsive lipid‐storage myopathy and glutaric aciduria type II of early adult onset

A 17-year-old girl with progressive lipid-storage myopathy for 2 years had low muscle carnitine levels. There was no therapeutic response to prednisone and DL-carnitine-HCl. Chemical findings indicated glutaric aciduria type II. Riboflavin therapy and a fat-restricted, carbohydrate-enriched diet resulted in dramatic improvement. Low carnitine concentrations in plasma and muscle were observed in three asymptomatic sisters who had normal urinary excretion patterns. There was impaired mitochondrial β-oxidation in cultured skin fibroblasts from the index patient and all three siblings.

Sarcoglycanopathies in Dutch patients with autosomal recessive limb girdle muscular dystrophy

Abstract Within a group of 76 sporadic/autosomal recessive limb girdle muscular dystrophy (LGMD) patients we tried to identify those with LGMD type 2C-E. Muscle biopsy specimens of 40 index patients, who had 22 affected sibs, were analyzed immuno-histochemically for the presence of three subunits: α-, β-, and γ,-sarcoglycans. Abnormal sarcoglycan expression was established in eight patients, with six affected sibs. In one patient γ-sarcoglycan was absent, and both α- and β-sarcoglycans were reduced. In the remaining seven patients γ-sarcoglycan was (slightly) reduced, and α- and β-sarcoglycans were absent or reduced. By DNA sequencing mutations were detected in one of the three sarcoglycan genes in all eight cases. Three patients had mutations in the α-, three in the β-, and two in the γ-sarcoglycan gene. The patients with sarcoglycanopathy comprised the more severely affected cases (P=0.04). In conclusion, sarcoglycanopathy was identified in 23% (14/62) of the autosomal recessive LGMD patients.

Genetic heterogeneity in Miyoshi-type distal muscular dystrophy

Miyoshi-type distal muscular dystrophy (MMD) is an autosomal recessively inherited progressive disorder. The putative locus of MMD is linked to the limb-girdle muscular dystrophy 2B locus on chromosome 2p12-14. In this study three of four MMD pedigrees show non-linkage to the region spanned by D2S134-D2S358-D2S145 on chromosome 2p, indicating genetic heterogeneity. A genome wide screen was performed to identify loci linked to MMD. In two non-chromosome 2-linked families, a 23 cM region on chromosome 10 segregated with MMD.

Genetic localization of Bethlem myopathy

Bethlem myopathy is a rare autosomal dominant myopathy characterized by slowly progressive limb-girdle muscular atrophy and weakness, and contractures of multiple joints. To identify the genetic localization we used highly polymorphic microsatellite markers in a genome-wide search in six Dutch families. After excluding genetic linkage with 52 markers distributed evenly over the autosomes, significant linkage was present with the 21q22.3 locus PFKL (two-point lod score of Zmax = 6.86 at theta = 0.03). There was no indication of genetic heterogeneity. The pattern of recombinations observed with adjacent markers indicated a localization distal to PFKL. Recombination of a marker within the collagen 6a1 gene (COL6A1) excluded this apparent candidate gene in one of the Bethlem myopathy families. The disease gene is most likely located in the region between COL6A1 and the telomere of chromosome 21q.

Genetic linkage of hereditary motor and sensory neuropathy type I (Charcot-Marie-Tooth disease) to markers of chromosomes 1 and 17

Hereditary motor and sensory neuropathy type 1 (HMSN I) is an autosomal dominant disorder genetically localized on chromosome 1 in a few families and on chromosome 17 in other families. We analyzed linkage between 6 markers of chromosome 1, 2 markers of chromosome 17, and the HMSN I locus using restriction fragment length polymorphisms and serotyping for the Duffy blood group in 5 families with HMSN I. Only in 1 of these families is linkage present between the disease locus and the loci for Duffy blood group and glucocerebrosidase (chromosome 1 markers). In the 4 other families the HMSN I locus is linked to the chromosome 17 markers pEW301 and pA10–41.

ALDP expression in fibroblasts of patients with X-linked adrenoleukodystrophy

SummaryThe adrenoleukodystrophy gene encodes a peroxisomal integral membrane protein (ALDP) consisting of 745 amino acids with a molecular weight of 75 kDa. ALDP expression was studied in fibroblasts from 24 male ALD patients from 17 unrelated ALD kindreds. In four kindreds an identical 2-base-pair deletion was found. We report the absence of ALDP in 12 kindreds carrying nonsense mutations, frame shifts or amino acid substitutions in the carboxy terminus of ALDP, together accounting for 71% of the ALD kindreds. ALDP was present in five kindreds (29%) with amino acid substitutions in the amino terminal half of the protein; in two of these kindreds ALDP was present although at a reduced level. The absence of truncated proteins suggests that the carboxy terminus has a function in the stabilization of ALDP.