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Pelizaeus-Merzbacher disease/X-linked spastic paraplegia (PMD/SPG2) comprises a spectrum of diseases that range from severe to quite mild. The reasons for the variation in severity are not obvious, but suggested explanations include the extent of disruption of the transmembrane portion of the proteolipid protein caused by certain amino acid substitutions and interference with the trafficking of the PLP molecule in oligodendrocytes. Four codons in which substitution of more than one amino acid has occurred are available for examination of clinical and potential structural manifestations: Valine165 to either glutamate or glycine, leucine 045 to either proline or arginine, aspartate 202 to asparagine or histidine, and leucine 223 to isoleucine or proline. Three of these mutations, Val165Gly, Leu045Pro, and Leu223Ile have not been described previously in humans. The altered amino acids appear in the A-B loop, C helix, and C-D loop, respectively. We describe clinically patients with the mutations T494G (Val165Gly), T134C (Leu045Pro), and C667A (Leu223Ile). We discuss also the previously reported mutations Asp202Asn and Asp202His. We have calculated the changes in hydrophobicity of short sequences surrounding some of these amino acids and compared the probable results of the changes in transmembrane structure of the proteolipid protein for the various mutations with the clinical data available on the patients. While the Val165Glu mutation, which is expected to produce disruption of a transmembrane loop of the protein, produces more severe disease than does Val165Gly, no particular correlation with hydrophobicity is found for the other mutations. As these are not in transmembrane domains, other factors such as intracellular transport or interaction between protein chains during myelin formation are probably at work.

A transition C506T was found in exon 4 of the proteolipid protein gene of a boy with spastic paraplegia. This mutation resulted in the substitution of phenylalanine for serine 169, which is in the third transmembrane domain of the proteolipid protein molecule. The mutation apparently arose de novo, as it was absent from his mother.

We report on a C-to-T transition in exon 6 of the PLP gene in a male with Pelizaeus-Merzbacher disease/X-linked spastic paraplegia. The transition changes a glutamine at amino acid residue 233 to a termination codon. This premature stop codon probably results in a truncated protein that is not functional. Six other relatives were analyzed for the mutation and two female carriers were identified. Autopsy data on one male are presented.

We report a G-->A transition at nucleotide 431 of the proteolipid protein gene (PLP) results in a nonsense codon in a family with an unusual form of Pelizaeus-Merzbacher disease (PMD). The mutation, which creates a second AluI restriction site, results in a nonsense mutation in PLP. The clinical picture resembles somewhat that of X-linked spastic paraplegia (SPG). It differs from this and both the classical and connatal forms of PMD in that it is relatively mild in form, onset is delayed beyond age 2 years, nystagmus is absent, tremors are prominent, mental retardation is not severe, some patients show dementia or personality disorders, the disease is progressive rather than static in some, and several females show signs of disease. The nonsense mutation, which is in exon 3B, should block the synthesis of normal PLP but spare DM20, the isoform whose persistence has been associated with mild forms of PLP-associated disease in both humans and mice.

Pelizaeus-Merzbacher disease (PMD) is an X-linked dysmyelinating disorder of the central nervous system. Many cases of PMD can be attributed to defects in the proteolipid protein gene (PLP). To date, with one exception, each family has had either no or a unique mutation in one of the seven exons of PLP. We describe a new missense mutation in exon 2 of the PLP gene of an affected individual. This mutation codes for Ile instead of Thr at codon 42. The point mutation originated in the X chromosome of the maternal great-grandfather of the propositus. This was determined from the pattern of inheritance of the AhaII polymorphism and a series of microsatellite markers that are localized near PLP at Xq22.

Single-strand conformational polymorphism analysis of an affected male with Pelizaeus-Merzbacher disease (PMD) showed a slight change in mobility of amplified exon 5 of the proteolipid protein (PLP) gene. The exon was sequenced and a G-->A transition at codon 216 was found. This mutation eliminates a BstNI restriction site and creates a MaeI restriction site. In 1989, Gencic et al. reported a mutation that destroyed the same BstNI site, but resulted in a substitution at codon 215 [Am J Hum Genet 45:435-442]. The mutation we report here is also present in the patient's mother and her male fetus as determined by polymerase chain reaction analysis of amniocytes.

We studied a female infant with clinical signs of Pelizaeus-Merzbacher disease (PMD), who has a familial mutation (C41-->T) in exon 2 of the proteolipid protein gene (PLP), and selected relatives. While the carrier mother and grandmother of the proposita currently are neurologically normal and show normal T2 magnetic resonance imaging (MRI) of the brain, the infant has a neurological picture, MRIs, and brain auditory evoked response (BAER) consistent with that diagnosis. The data here presented show that PMD can occur in females carrying a mutation in the PLP gene. Our experience with the MRIs of this patient, her mother and grandmother, and those of a previously reported family [Pratt et al.: Am J Med Genet 38:136-139, 1991] show that molecular genetic analysis and not MRI is the appropriate means for carrier detection.

We describe an in-frame deletion of parts of exons 3 and 4 of the proteolipid protein gene (PLP), with all of the intervening sequence, in a 3-generation family with Pelizaeus-Merzbacher disease. The mutation removes 49 amino acids of the PLP.

A C--greater than G transversion has been found in exon 3 of the PLP gene of affected males and their mother in a single sibship with Pelizaeus-merzbacher disease (PMD). The transversion should not result in an amino acid change in the protein but it does result in the loss of a HaeIII restriction endonuclease cleavage site. It is concordant with the disease in this family. One-hundred-ten unrelated X chromosomes are negative for this mutation. No other sequence defect was found in the PLP exons of the affected males. The cause of disease in this family remains unknown, but the association between this rare mutation and PMD is intriguing. The mutation can serve as a marker for following segregation of the PLP gene.

A C-to-T transition in exon 4 of the PLP gene was found in 2 affected males and two obligate carriers in a German family with Pelizaeus-Merzbacher disease. The mutation, which causes loss of an HphI site and changes amino acid 155 from threonine to isoleucine, was absent from 108 normal chromosomes. There are 5 concordances and 1 discrepancy between these results and those obtained by magnetic resonance imaging in this family.

Denaturing gradient gel electrophoresis (DGGE) can detect single-base changes in DNA. We used site-directed mutagenesis to produce all six possible single-base substitutions at a splice acceptor consensus AG dinucleotide within the mouse adenine phosphoribosyltransferase (aprt) gene. Studies of mouse and Chinese hamster cell aprt indicate a high level of both spontaneous and induced mutations in this region. We systematically evaluated each of the six mutations by DGGE. Five of the six mutant sequences could be distinguished from wildtype by DGGE analysis of a 560-bp fragment containing the mutation. However, one mutant could not be distinguished from wild-type, and some of the mutant constructs could not be distinguished from each other. Analysis of DNA heteroduplexes consisting of wild-type and mutant strands or two different mutant strands enabled all mutant constructs to be distinguished from wild-type and from each other. The pairwise mixtures resulted in 24 different heteroduplexes, all of which were less stable than the parental homoduplexes. End labeling of DNA prior to heteroduplex formation and subsequent DGGE analysis enabled us to determine the relative destabilization caused by different types of single-base mismatches.

X-linked nephrogenic diabetes insipidus (NDI) was segregating in a large Indiana family. It was tested for linkage of the NDI gene to X-chromosome molecular markers. Maximum lod scores of 3.15 and 3.01 (theta = 0) obtained for the molecular markers F8A (F8C) and DXS15 (DX13) respectively, indicate that the NDI gene is located in Xq28. A lod score of 3.61 (theta = 0) was obtained with multipoint linkage analysis of F8A and DXS15.