Ann B. Moser

Mutations in the PTS1 receptor gene, PXR1, define complementation group 2 of the peroxisome biogenesis disorders.

The peroxisome biogenesis disorders (PBDs) are lethal recessive diseases caused by defects in peroxisome assembly. We have isolated PXR1, a human homologue of the yeast P. pastoris PAS8 (peroxisome assembly) gene. PXR1, like PAS8, encodes a receptor for proteins with the type–1 peroxisomal targeting signal (PTS1). Mutations in PXR1 define complementation group 2 of PBDs and expression of PXR1 rescues the PTS1 import defect of fibroblasts from these patients. Based on the observation that PXR1 exists both in the cytosol and in association with peroxisomes, we propose that PXR1 protein recognizes PTS1 –containing proteins in the cytosol and directs them to the peroxisome.

Human PEX7 encodes the peroxisomal PTS2 receptor and is responsible for rhizomelic chondrodysplasia punctata

Rhizomelic chondrodysplasia punctata (RCDP) is a rare autosomal recessive phenotype that comprises complementation group 11 of the peroxisome biogenesis disorders (PBD). PEX7, a candidate gene for RCDP identified in yeast, encodes the receptor for peroxisomal matrix proteins with the type-2 peroxisome targeting signal (PTS2). By homology probing we identified human and murine PEX7 genes and found that expression of either corrects the PTS2-import defect characteristic of RCDP cells. In a collection of 36 RCDP probands, we found two inactivating PEX7 mutations: one, L292ter, was present in 26 of the probands, all with a severe phenotype; the second, A218V, was present in three probands, including two with a milder phenotype. A third mutation, G217R, whose functional significance is yet to be determined, was present in five probands, all compound heterozygotes with L292ter. We conclude that PEX7 is responsible for RCDP (PBD CG11) and suggest a founder effect may explain the high frequency of L292ter.

Adrenoleukodystrophy Increased plasma content of saturated very long chain fatty acids

With a new method we measured the saturated very long chain fatty acids in the plasma of adrenoleukodystrophy (ALD) hemizygotes, ALD heterozygotes, and controls. ALD hemizygotes showed increased levels of hexacosanoate (C26 fatty acid) which represented 0.081 2 0.0066% (SEM) of total Fatty acids, compared to 0.015 ± 0.0032% in the controls. C25, C24, and C23 fatty acids were also increased, but the C22 and C20 fatty acids were normal. C26 levels were also increased in most ALD heterozygotes, with a mean level 0.057 2 0.0063% of total fatty acids. The technique can be used for diagnosis and carrier identification, and in the evaluation of therapy.With a new method we measured the saturated very long chain fatty acids in the plasma of adrenoleukodystrophy (ALD) hemizygotes, ALD heterozygotes, and controls. ALD hemizygotes showed increased levels of hexacosanoate (C26 fatty acid) which represented 0.081 ± 0.0066% (SEM) of total fatty acids, compared to 0.015 ± 0.0032% in the controls. C25, C24, and C23 fatty acids were also increased, but the C22 and C20 fatty acids were normal. C26 levels were also increased in most ALD heterozygotes, with a mean level 0.057± 0.0063% of total fatty acids. The technique can be used for diagnosis and carrier identification, and in the evaluation of therapy.

Functions of plasmalogen lipids in health and disease

Plasmalogens are a unique class of membrane glycerophospholipids containing a fatty alcohol with a vinyl-ether bond at the sn-1 position, and enriched in polyunsaturated fatty acids at the sn-2 position of the glycerol backbone. These two features provide novel properties to these compounds. Although plasmalogens represent up to 20% of the total phospholipid mass in humans their physiological roles have been challenging to identify, and are likely to be particular to different tissues, metabolic processes and developmental stages. Their biosynthesis starts in peroxisomes, and defects at these steps cause the malformation syndrome, Rhizomelic Chondrodysplasia Punctata (RCDP). The RCDP phenotype predicts developmental roles for plasmalogens in bone, brain, lens, lung, kidney and heart. Recent studies have revealed secondary plasmalogen deficiencies associated with more common disorders and allow us to tease out additional pathways dependent on plasmalogen functions. In this review, we present current knowledge of plasmalogen biology in health and disease.

Adrenoleukodystrophy: Incidence, new mutation rate, and results of extended family screening

Utilizing the plasma very long chain fatty acid assay, supplemented by mutation analysis and immunofluorescence assay, we determined the number of X‐linked adrenoleukodystrophy (X‐ALD) hemizygotes from the United States identified each year in the two laboratories that perform most of the assays in this country: the Kennedy Krieger Institute between 1981 and 1998 and the Mayo Clinic Rochester from 1996 to 1998. The minimum frequency of hemizygotes identified in the United States is estimated to be 1:42,000 and that of hemizygotes plus heterozygotes 1:16,800. Our studies involved 616 pedigrees with a total of 12,787 identified at‐risk members. Diagnostic assays were performed in 4,169 at‐risk persons (33%) and included members of the extended family. Only 5% of male probands and 1.7% of X‐ALD hemizygotes were found to have new mutations. The extended family testing led to the identification of 594 hemizygotes and 1,270 heterozygotes. Two hundred fifty of the newly identified hemizygotes were asymptomatic and represent the group in which therapy has the greatest chance of success. Identification of heterozygotes provides the opportunity for disease prevention through genetic counseling. Diagnostic tests should be offered to all at‐risk relatives of X‐ALD patients and should include members of the extended family. Ann Neurol 2001;49:512–517

Gene redundancy and pharmacological gene therapy: Implications for X- linked adrenoleukodystrophy

As more functional redundancy in mammalian cells is discovered, enhanced expression of genes involved in alternative pathways may become an effective form of gene therapy. X-linked adrenoleukodystrophy (X-ALD) is a peroxisomal disorder with impaired very-long-chain fatty acid metabolism. The X-ALD gene encodes a peroxisomal membrane protein (ALDP) that is part of a small family of related peroxisomal membrane proteins. We show that 4-phenylbutyrate treatment of cells from both X-ALD patients and X-ALD knockout mice results in decreased levels of and increased β-oxidation of very-long-chain fatty acids; increased expression of the peroxisomal protein ALDRP; and induction of peroxisome proliferation. We also demonstrate that ALDP and ALDRP are functionally related, by ALDRP cDNA complementation of X-ALD fibroblasts. Finally, we demonstrate the in vivo efficacy of dietary 4-phenylbutyrate treatment through its production of a substantial reduction of very-long-chain fatty acid levels in the brain and adrenal glands of X-ALD mice.

Clinical and biochemical spectrum of patients with RSH/Smith-Lemli-Opitz syndrome and abnormal cholesterol metabolism

RSH/Smith-Lemli-Opitz (RSH/SLO) syndrome is an autosomal recessive malformation syndrome recently shown to be associated with a severe deficiency of cholesterol biosynthesis and markedly elevated plasma and tissue levels of 7-dehydrocholesterol (7-DHC), the immediate precursor of cholesterol in the Kandutsch-Russell biosynthetic pathway. Because these biochemical abnormalities permit a reassessment of RSH/SLO on biochemical criteria rather than less specific physical criteria, we review here the clinical and biochemical characteristics of our first 80 patients with abnormally increased levels of 7-DHC. The study population included 68 index patients and 12 additional relatives identified by quantification of 7-DHC and cholesterol in plasma, amniotic fluid, or cultured fibroblasts, lymphoblasts, or amniocytes. As demonstrated in other clinical syndromes when redefined biochemically, we have found a wider range of clinical expression of RSH/SLO than previously recognized. These newly recognized atypical RSH/SLO patients included several with no malformations other than syndactyly of the toes and, at the other extreme, patients with frank holoprosencephaly or multiple visceral anomalies who died in utero. Syndactyly of toes 2 and 3 was the most common malformation, occurring in all but one of 80 patients. The best biochemical predictor of clinical severity was the plasma cholesterol level, which decreased with increasing clinical severity. However, at least 10% of patients, including one newborn infant, had normal cholesterol levels at the time of diagnosis and would have been missed without specific quantification of 7-DHC. Not unexpectedly, several patients carrying a clinical diagnosis of RSH/SLO were found to have normal levels of all plasma sterols and apparently normal cholesterol biosynthesis in cultured cells. A comparison of the frequency of anomalies in our biochemically identified patients with similar data from previously reported clinical series suggests that up to 25% of reports of RSH/SLO in the literature may describe genetic conditions other than RSH/SLO with 7-DHC-emia.

Phenotype of patients with peroxisomal disorders subdivided into sixteen complementation groups

OBJECTIVE To use the technique of complementation analysis to help define genotype and classify patients with clinical manifestations consistent with those of the disorders of peroxisome assembly, namely the Zellweger syndrome (ZS), neonatal adrenoleukodystrophy (NALD), infantile Refsum disease (IRD), and rhizomelic chondrodysplasia punctata (RCDP). STUDY DESIGN Clinical findings, peroxisomal function, and complementation groups were examined in 173 patients with the clinical manifestations of these disorders. RESULTS In 37 patients (21%), peroxisome assembly was intact and isolated deficiencies of one of five peroxisomal enzymes involved in the beta-oxidation of fatty acids or plasmalogen biosynthesis were demonstrated. Ten complementation groups were identified among 93 patients (54%) with impaired peroxisome assembly and one of three phenotypes (ZS, NALD, or IRD) without correlation between complementation group and phenotype. Forty-three patients (25%) had impaired peroxisome assembly associated with the RCDP phenotype and belonged to a single complementation group. Of the 173 patients, 10 had unusually mild clinical manifestations, including survival to the fifth decade or deficits limited to congenital cataracts. CONCLUSIONS At least 16 complementation groups, and hence genotypes, are associated with clinical manifestations of disorders of peroxisome assembly. The range of phenotype is wide, and some patients have mild involvement.

The inflammatory myelinopathy of adreno-leukodystrophy : cells, effector molecules, and pathogenetic implications

Prominent inflammation in the demyelinative lesion of adreno-leukodystrophy (ALD) has suggested an immune-mediated pathogenetic component. Commercially available antibodies to T cells, B cells, macrophages, class I and II molecules, complement, IgG, IgM, IgA, interleukin-1 (IL-1), intercellular adhesion molecule-1 (ICAM-1) and tumor necrosis factor-alpha (TNF) were applied to paraffin sections of formaldehyde-fixed postmortem samples. Twenty-five primary demyelinative lesions from five juvenile ALD, three adult ALD, and three adrenomyeloneuropathic patients were evaluated with appropriate positive and negative controls. Macrophages and astrocytes were the predominant cells detected at the active edge; T lymphocytes, including T4 and CD45R subsets, were nearly as numerous but usually located around vessels within the lesion. B cells and plasma cells, usually containing IgG, were uncommon. The expression of class II molecules, restricted to one adult, was problematic; class I expression was increased in microvascular and other cells. Degraded myelin was labeled with antibodies to C3d and IL-1; IL-1 and ICAM-1 immunoreactivity was seen on microvessels and astrocytes. Tumor necrosis factor-alpha immunoreactivity was detected in macrophages, but more prominently in astrocytes. These data support a natural immune response in the demyelinative lesion of ALD, consisting predominantly of reactive astrocytes, macrophages, T cells and cytokines. A two-stage pathogenetic theory is discussed. The postulated roles of TNF and reactive astrocytes, in concert with a fundamental myelinolytic biochemical defect, suggest a different pathogenetic mechanism and raise novel therapeutic possibilities.

Mutations in the gene encoding 3β-hydroxysteroid-Δ8,Δ7-isomerase cause X-linked dominant Conradi-Hunermann syndrome

X-linked dominant Conradi-Hünermann syndrome (CDPX2; MIM 302960) is one of a group of disorders with aberrant punctate calcification in cartilage, or chondrodysplasia punctata (CDP). This is most prominent around the vertebral column, pelvis and long bones in CPDX2. Additionally, CDPX2 patients may have asymmetric rhizomesomelia, sectorial cataracts, patchy alopecia, ichthyosis and atrophoderma. The phenotype in CDPX2 females ranges from stillborn to mildly affected individuals identified in adulthood. CDPX2 is presumed lethal in males, although a few affected males have been reported,. We found increased 8(9)-cholestenol and 8-dehydrocholesterol in tissue samples from seven female probands with CDPX2 ( ref. 4). This pattern of accumulated cholesterol intermediates suggested a deficiency of 3β-hydroxysteroid-Δ8,Δ 7-isomerase (sterol-Δ8-isomerase), which catalyses an intermediate step in the conversion of lanosterol to cholesterol. A candidate gene encoding a sterol-Δ8-isomerase ( EBP) has been identified and mapped to Xp11.22–p11.23 (Refs 5,6). Using SSCP analysis and sequencing of genomic DNA, we found EBP mutations in all probands. We confirmed the functional significance of two missense alleles by expressing them in a sterol-Δ8-isomerase-deficient yeast strain. Our results indicate that defects in sterol-Δ8-isomerase cause CDPX2 and suggest a role for sterols in bone development.