De novo loss of function mutations in KIAA2022 are associated with epilepsy and neurodevelopmental delay in females.

Intellectual disability (ID) affects about 3% of the population and has a male gender bias. Of at least 700 genes currently linked to ID, more than 100 have been identified on the X chromosome, including KIAA2022. KIAA2022 is located on Xq13.3 and is expressed in the developing brain. The protein product of KIAA2022, X­linked Intellectual Disability Protein Related to Neurite Extension (XPN), is developmentally regulated and is involved in neuronal migration and cell adhesion. The clinical manifestations of loss­of­function KIAA2022 mutations have been described previously in 15 males, born from unaffected carrier mothers, but few females. Using whole­exome sequencing, we identified a cohort of five unrelated female patients with de novo probably gene damaging variants in KIAA2022 and core phenotypic features of ID, developmental delay, epilepsy refractory to treatment, and impaired language, of similar severity as reported for male counterparts. This study supports KIAA2022 as a novel cause of X­linked dominant ID, and broadens the phenotype for KIAA2022 mutations.

Childhood Cerebral Adrenoleukodystrophy: MR Perfusion Measurements and Their Use in Predicting Clinical Outcome after Hematopoietic Stem Cell Transplantation.

BACKGROUND AND PURPOSE: MR perfusion has shown abnormalities of affected WM in cerebral X-linked adrenoleukodystrophy, but serial data is needed to explore the import of such findings after hematopoietic stem cell transplantation. Our aim was to prospectively measure MR perfusion parameters in patients with cerebral adrenoleukodystrophy pre- and post-hematopoietic stem cell transplantation, and to correlate those measurements with clinical outcome. MATERIALS AND METHODS: Ten patients with cerebral adrenoleukodystrophy prospectively underwent DSC-MR perfusion imaging at <45 days pre- (baseline), 30-60 days post-, and 1 year post-hematopoietic stem cell transplantation. MR perfusion measurements in the 10 patients and 8 controls were obtained from the parieto-occipital WM, splenium of the corpus callosum, leading enhancing edge, and normal-appearing frontal white matter. MR imaging severity scores and clinical neurologic function and neurocognitive scores were also obtained. MR perfusion values were analyzed in the patients with cerebral adrenoleukodystrophy at each time point and compared with those in controls. Correlations were calculated between the pre-hematopoietic stem cell transplantation MR perfusion values and 1-year clinical scores, with P value adjustment for multiple comparisons. RESULTS: At baseline in patients with cerebral adrenoleukodystrophy, both relative CBV and relative CBF within the splenium of the corpus callosum and parieto-occipital WM significantly differed from those in controls (P = .005-.031) and remained so 1 year post-hematopoietic stem cell transplantation (P = .003-.005). Meanwhile, no MR perfusion parameter within the leading enhancing edge differed significantly from that in controls at baseline or at 1 year (P = .074-.999) or significantly changed by 1 year post-hematopoietic stem cell transplantation (P = .142-.887). Baseline Loes scores correlated with 1-year clinical neurologic function (r = 0.813, P < .0001), while splenium of the corpus callosum relative CBV also significantly correlated with 1-year neurologic function scale and the neurocognitive full-scale intelligence quotient and performance intelligence quotient scores (r = -0.730-0.815, P = .007-.038). CONCLUSIONS: Leading enhancing edge measurements likely remain normal post-hematopoietic stem cell transplantation in cerebral adrenoleukodystrophy, suggesting local disease stabilization. Meanwhile, parieto-occipital WM and splenium of the corpus callosum relative CBV and relative CBF values worsened; this change signified irreversible injury. Baseline splenium of the corpus callosum relative CBV may predict clinical outcomes following hematopoietic stem cell transplantation.

Intensity of MRI Gadolinium Enhancement in Cerebral Adrenoleukodystrophy: A Biomarker for Inflammation and Predictor of Outcome following Transplantation in Higher Risk Patients.

BACKGROUND AND PURPOSE: Outcomes following hematopoietic stem cell transplantation for higher risk childhood-onset cerebral adrenoleukodystrophy are variable. We explored whether a brain MR imaging gadolinium intensity scoring system improves prediction of neurologic outcome. MATERIALS AND METHODS: We developed a 4-point scale of gadolinium intensity relative to the choroid plexus: 0 = no enhancement; 1 = hypointense; 2 = isointense; 3 = hyperintense. The interobserver concordance of the scale was assessed on 30 randomly chosen studies. Scores were generated for 64 evaluable patients and compared with CSF chitotriosidase levels, a known inflammatory marker correlating with outcomes following transplantation. For 25 evaluable higher risk patients (Loes ≥10), the gadolinium intensity score was compared with longer term posttransplantation clinical change. RESULTS: The gadolinium intensity scoring system showed good interobserver reproducibility (κ = 0.72). Of 64 evaluable boys, the score positively correlated with average concomitant CSF chitotriosidase activity in nanograms/milliliter/hour: 0: 2717, n = 5; 1: 3218, n = 13; 2: 6497, n = 23; and 3: 12,030, n = 23 (P < .01). For 25 evaluable higher risk patients, more intense pretransplantation brain MR imaging gadolinium enhancement predicted greater average loss on the adrenoleukodystrophy neurologic function scale following transplantation: 0/1: adrenoleukodystrophy neurologic function scale score difference = 4.3, n = 7; 2/3: adrenoleukodystrophy neurologic function scale score difference = 10.4, n = 18 (P = .05). CONCLUSIONS: Gadolinium enhancement intensity on brain MR imaging can be scored simply and reproducibly for cerebral adrenoleukodystrophy. The enhancement score significantly correlates with chitotriosidase. In boys with higher risk cerebral disease (Loes ≥10), the enhancement score itself predicts neurologic outcome following treatment. Such data may help guide treatment decisions for clinicians and families.

Newborn screening for X-linked adrenoleukodystrophy in New York State: diagnostic protocol, surveillance protocol and treatment guidelines.

PURPOSE: To describe a diagnostic protocol, surveillance and treatment guidelines, genetic counseling considerations and long-term follow-up data elements developed in preparation for X-linked adrenoleukodystrophy (X-ALD) newborn screening in New York State. METHODS: A group including the director from each regional NYS inherited metabolic disorder center, personnel from the NYS Newborn Screening Program, and others prepared a follow-up plan for X-ALD NBS. Over the months preceding the start of screening, a series of conference calls took place to develop and refine a complete newborn screening system from initial positive screen results to long-term follow-up. RESULTS: A diagnostic protocol was developed to determine for each newborn with a positive screen whether the final diagnosis is X-ALD, carrier of X-ALD, Zellweger spectrum disorder, acyl CoA oxidase deficiency or D-bifunctional protein deficiency. For asymptomatic males with X-ALD, surveillance protocols were developed for use at the time of diagnosis, during childhood and during adulthood. Considerations for timing of treatment of adrenal and cerebral disease were developed. CONCLUSION: Because New York was the first newborn screening laboratory to include X-ALD on its panel, and symptoms may not develop for years, long-term follow-up is needed to evaluate the presented guidelines.

Onset of adreno-leukodystrophy after medulloblastoma therapy: causal connection or coincidence?

X-linked adreno-leukodystrophy (ALD) is a peroxisomal disorder affecting the white matter of the central nervous system and the adrenal cortex. It is caused by mutations in the ABCD1 gene encoding for a peroxisomal membrane protein. The absent genotype-phenotype correlation implies a contribution by environmental factors to explain the phenotypical heterogeneity. We report on a 4-year-old boy with a biochemically confirmed diagnosis of ALD after birth. At the age of 32 months, the additional diagnosis of a medulloblastoma was made. After treatment of the medulloblastoma, he developed active areas of demyelination representing the characteristic neuroimaging features of ALD. The clinical history of our patient supports the hypothesis that external factors, like neurosurgical intervention as part of medulloblastoma treatment, may accelerate or initiate cerebral ALD-related demyelination. A postsurgical inflammatory reaction may facilitate the inclusion of abnormal fatty acids in myelin. The opening of the blood-brain barrier following neurosurgery may enhance the recognition of previously sequestered antigens considered to play a role in ALD onset. Consequently, neurosurgical disruption of the BBB can precipitate the immune-mediated inflammatory process, which progressively destroys myelin in ALD patients. Tumor-related chemotherapy and/or radiotherapy may also play a contributing role. We suggest that X-ALD patients who undergo neurosurgical intervention need close follow-up imaging to identify active demyelination early.

Contrast enhancement of brainstem tracts in Zellweger spectrum disorder: evidence of inflammatory demyelination?

Zellweger spectrum disorder, resulting from mutations in the peroxisome assembly mechanism, is genetically heterogeneous and phenotypically varied in disease characteristics and severity. In addition to manifesting gyration anomalies, affected individuals typically have white matter abnormalities ranging from hypomyelination in infancy to a more diffuse demyelinating leukoencephalopathy pattern in those surviving into childhood. Here we report a unique presentation in a 2/-year-boy with acute neurological deterioration and MRI demonstrating avid contrast enhancement suggesting inflammatory demyelination in the brainstem.

Docosahexaenoic acid therapy in peroxisomal diseases: results of a double-blind, randomized trial.

OBJECTIVES: Peroxisome assembly disorders are genetic disorders characterized by biochemical abnormalities, including low docosahexaenoic acid (DHA). The objective was to assess whether treatment with DHA supplementation would improve biochemical abnormalities, visual function, and growth in affected individuals. METHODS: This was a randomized, double-blind, placebo-controlled trial conducted at a single center. Treatment groups received supplements of DHA (100 mg/kg per day). The primary outcome measures were the change from baseline in the visual function and physical growth during the 1 year follow-up period. RESULTS: Fifty individuals were enrolled and randomized. Two were subsequently excluded from study analysis when it was determined that they had a single enzyme disorder of peroxisomal beta oxidation. Thirty-four returned for follow-up. Nine patients died during the trial of their disorder, and 5 others were lost to follow-up. DHA supplementation was well tolerated. There was no difference in the outcomes between the treated and untreated groups in biochemical function, electroretinogram, or growth. Improvements were seen in both groups in certain individuals. CONCLUSIONS: DHA supplementation did not improve the visual function or growth of treated individuals with peroxisome assembly disorders. CLASSIFICATION OF EVIDENCE: This interventional study provides Class II evidence that DHA supplementation did not improve the visual function or growth of treated individuals with peroxisome assembly disorders during an average of 1 year of follow-up in patients aged 1 to 144 months.

A PEX10 defect in a patient with no detectable defect in peroxisome assembly or metabolism in cultured fibroblasts.

Zellweger spectrum disorders (ZSD) are diagnosed by biochemical assay in blood, urine and cultured fibroblasts and PEX gene mutation identification. In most cases studies in fibroblasts corroborate results obtained in body fluids. In 1996 Clayton and colleagues described a 10-year old girl with evidence of a peroxisome disorder, based on elevated bile acid metabolites and phytanate. At the time it was not possible to distinguish whether she had a ZSD or a single peroxisomal protein defect. Studies in our laboratory showed that she also had elevated plasma pipecolate, supporting the former diagnosis. Despite the abnormal metabolites detected in blood (phytanate, bile acid intermediates and pipecolate), analysis of multiple peroxisomal pathways in fibroblasts yielded normal results. In addition, she had a milder clinical phenotype than usually associated with ZSD. Since complementation analysis to determine the gene defect was not possible, we screened this patient following the PEX Gene Screen algorithm (PGS). The PGS provides a template for sequencing PEX gene exons independent of complementation analysis. Two mutations in PEX10 were identified, a frameshift mutation inherited from her father and a de novo missense mutation in a conserved functional domain on the other allele. This case highlights that molecular analysis may be essential to the diagnosis of patients at the milder end of the ZSD spectrum. Furthermore, it supports the concept that some tissues are less affected by certain PEX gene defects than brain and liver.

Essential fatty acid profiling for routine nutritional assessment unmasks adrenoleukodystrophy in an infant with isovaleric acidaemia.

We report a 16-month-old asymptomatic male with enzyme confirmed isovaleric acidaemia (IVA; isovaleryl-CoA dehydrogenase deficiency; OMIM 243500) who, upon routine nutritional follow-up, presented evidence of peroxisomal dysfunction. The newborn screen (2 days of life) revealed elevated C(5)-carnitine (2.95 µmol/L; cutoff <0.09 µmol/L) and IVA was subsequently confirmed by metabolic profiling and in vitro enzymology. Plasma essential fatty acid (EFA) analysis, assessed to evaluate nutritional status during protein restriction and L: -carnitine supplementation, revealed elevated C(26:0) (5.0 µmol/L; normal <1.3). Subsequently, metabolic profiling and molecular genetic analysis confirmed X-linked adrenoleukodystrophy (XALD). Identification of co-inherited XALD with IVA in this currently asymptomatic patient holds significant treatment ramifications for the proband prior to the onset of neurological sequelae, and critically important counselling implications for this family.

Magnetization transfer MRI demonstrates spinal cord abnormalities in adrenomyeloneuropathy.

BACKGROUND: In adrenomyeloneuropathy (AMN) conventional MRI detects only spinal cord atrophy in the late stages. OBJECTIVE: To apply a magnetization transfer-weighted (MTw) imaging to patients with AMN and AMN-like syndrome in order to visualize and quantitatively assess the pathology of white matter tracts in the cervical spinal cord. METHODS: MTw studies were conducted in nine men with AMN, eight symptomatic heterozygous women, and 10 age- and sex-matched controls and compared to the Expanded Disability Status Scale (EDSS) and quantitative tests of vibratory sense and postural sway. MTw data sets were obtained at the level of C1 to C3 using a three-dimensional gradient echo acquisition technique, these images were then standardized between subjects by using the in-slice CSF signal as a normalization reference, allowing a quantitative assessment of the MTw signal. RESULTS: In contrast to conventional MRI, MTw images showed signal hyperintensities in the lateral and dorsal columns of all patients. The MT signal quantified in the dorsal column showed significant differences between patients with AMN, X-linked adrenoleukodystrophy heterozygotes, and controls. MT hyperintensity in the dorsal column correlated with EDSS, vibratory sense, and postural sway. CONCLUSION: Magnetization transfer-weighted imaging is a sensitive modality for the visual and quantitative assessment of spinal cord pathology in adrenomyeloneuropathy, and is a potential tool for evaluation of new therapies.

Spectroscopic evidence of cerebral axonopathy in patients with "pure" adrenomyeloneuropathy.

BACKGROUND: Adrenomyeloneuropathy (AMN) is the adult variant of X-linked adrenoleukodystrophy. The disease pathology is usually limited to spinal cord and peripheral nerves, and when this is the case, it is referred to as "pure" AMN. Histopathology shows cerebral involvement even in pure AMN; however, not much is known about the nature, extent, and clinical relevance of these findings. OBJECTIVE: To investigate brain involvement in AMN patients with normal MRI, employing multislice MR spectroscopic imaging. METHODS: Twelve men with pure AMN were compared with 19 age-matched healthy volunteers. Metabolite ratios (N-acetylaspartate [NAA]/choline [Cho], NAA/creatine [Cr], and Cho/Cr) were measured from seven brain regions. Global metabolite ratios were generated as an average of these seven regional ratios. The Expanded Disability Status Scale (EDSS) was used for neurologic evaluation. RESULTS: The patients with AMN showed reduced global NAA/Cho (AMN 1.40 +/- 0.16 vs controls 1.75 +/- 0.34; p = 0.003)) and global NAA/Cr (AMN 2.32 +/- 0.13 vs controls 2.62 +/- 0.43; p = 0.03). Regionally, NAA/Cho was lowered in the internal capsule (AMN 1.30 +/- 0.20 vs controls 1.69 +/- 0.37; p = 0.002) and in parieto-occipital white matter (AMN 1.45 +/- 0.19 vs controls 1.78 +/- 0.55; p = 0.04). NAA/Cr was lowered in parieto-occipital white matter (AMN 2.34 +/- 0.31 vs controls 2.83 +/- 0.71; p = 0.04). EDSS demonstrated an inverse association with global NAA/Cr (r = -0.65, p = 0.02) and NAA/Cr in centrum semiovale (r = -0.73, p = 0.006) and in parieto-occipital white matter (r = -0.64, p = 0.02). Cho/Cr was not significantly elevated. CONCLUSIONS: (1)H-MR spectroscopic imaging is able to detect biochemical abnormalities suggestive of axonal damage even in the brains of patients with pure adrenomyeloneuropathy. The axonopathy is most prominent in internal capsule and parieto-occipital white matter and may contribute to clinical disability.

Analysis of MRI patterns aids prediction of progression in X-linked adrenoleukodystrophy.

BACKGROUND: X-linked adrenoleukodystrophy (X-ALD) has variants with widely different outcomes, hampering clinical counseling and evaluation of therapies. OBJECTIVE: To evaluate the degree to which MRI patterns can predict lesion progression. METHODS: Two hundred six boys and men with cerebral X-ALD (median age 12.2 years, mean age 18.5 years, age range 1.7 to 73.8 years) were studied. In 140 individuals, follow-up MRI were available. Data after bone marrow transplantation (BMT) were excluded. The patterns of MRI abnormalities were subdivided into five groups based on the anatomic location of the initial T2 signal hyperintensity (pattern 1: parieto-occipital white matter, pattern 2: frontal white matter, pattern 3: corticospinal tract, pattern 4: cerebellar white matter, pattern 5: concomitant parieto-occipital and frontal white matter). The X-ALD MRI Severity Scale, a 34-point scale previously described, was used in the analysis. RESULTS: Pattern 1 patients had rapid progression if contrast enhancement was present and if the MRI abnormality manifested at an early age. The latter was also true for pattern 2 patients. Based on these variables, predictive formulas were constructed for these two patterns using multiple regressions. MRI progression was much slower in pattern 3 and 4 patients, whereas in the few pattern 5 patients, it was more rapid than in any other of the patterns. Patterns 1 and 5 occurred mainly in childhood, patterns 2 and 4 in adolescence, and pattern 3 in adults. CONCLUSIONS: MRI progression in X-ALD depends on patient age, initial MRI Severity Scale score, and anatomic location of the lesion. When used in combination, these data aid the prediction of disease course and the selection of patients for BMT.

MRI and proton MRSI in women heterozygous for X-linked adrenoleukodystrophy.

OBJECTIVE: To utilize neuroimaging procedures to assess the extent of cerebral involvement in female subjects heterozygous for X-linked adrenoleukodystrophy (X-ALD). METHODS: Brain MRI studies were performed in 76 female subjects heterozygous for X-ALD (mean age 43 years, range 8 to 75 years). Sixty-five had clinical evidence of spinal cord involvement resembling that in males with adrenomyeloneuropathy (AMN), two had clinical evidence of cerebral involvement, and nine showed no neurologic abnormality. Readers blinded to clinical findings further analyzed abnormal MRI studies. In eight women whose MRI results were normal, four-slice long echo time MRS imaging (MRSI) studies were performed and compared to those of eight age-matched controls. RESULTS: MRI results were normal in 65 subjects and abnormal in 11. In eight of the latter group, the MRI changes were judged to be due to causes other than X-ALD. Lesions were attributed to X-ALD in the remaining three. Two of these patients had lesions that resembled those in male patients with cerebral X-ALD. In one patient with a mild AMN-like syndrome, brain MRI abnormalities were confined to the corticospinal tract. When compared to those of controls, MRSI studies in eight female patients with normal results on brain MRI showed a significant reduction of N-acetylaspartate/creatine and N-acetylaspartate/choline ratios in the internal capsule and corticospinal projection fibers. The N-acetylaspartate/choline ratio was significantly reduced in the parieto-occipital white matter and the choline/creatine ratio was significantly increased in the frontal white matter. CONCLUSION: Brain involvement demonstrable by MRI is rare in female subjects heterozygous for X-ALD, including those who have clinical evidence of spinal cord involvement. Nevertheless, N-acetylaspartate levels are reduced in the corticospinal projection fibers in female subjects with normal results on MRI, suggesting axonal dysfunction.

Molecular findings in symptomatic and pre-symptomatic Alexander disease patients.

BACKGROUND AND OBJECTIVE: Alexander disease is a slowly progressive CNS disorder that most commonly occurs in children. Until recently, the diagnosis could only be established by the histologic finding of Rosenthal fibers in brain specimens. Mutations in the glial fibrillary acidic protein (GFAP) gene have now been shown in a number of biopsy- or autopsy-proven patients with Alexander disease. A prospective study on patients suspected to have Alexander disease was conducted to determine the extent to which clinical and MRI criteria could accurately diagnose affected individuals, using GFAP gene sequencing as the confirmatory assay. METHODS: Patients who showed MRI white matter abnormalities consistent with Alexander disease, unremarkable family history, normal karyotype, and normal metabolic screening were included in this study. Genomic DNA from patients was screened for mutations in the entire coding region, including the exon-intron boundaries, of the GFAP gene. RESULTS: Twelve of 13 patients (approximately 90%) were found to have mutations in GFAP. Seven of those 12 patients presented in infancy with seizures and megalencephaly. Five were juvenile-onset patients with more variable symptoms. Two patients in the latter group were asymptomatic or minimally affected at the time of their initial MRI scan. The mutations were distributed throughout the gene, and all involved sporadic single amino acid heterozygous changes that changed the charge of the mutant protein. Four of the nine changes were novel mutations. CONCLUSIONS: In symptomatic and asymptomatic patients with a predominantly frontal leukoencephalopathy by MRI, GFAP gene mutation analysis should be included in the initial diagnostic evaluation process for Alexander disease.

Proton MR spectroscopic imaging predicts lesion progression on MRI in X-linked adrenoleukodystrophy.

BACKGROUND: The phenotypic expression of X-linked adrenoleukodystrophy (X-ALD) ranges from the rapidly progressive childhood cerebral form to the milder adrenomyeloneuropathy in adults. It is not possible to predict phenotype by mutation analysis or biochemical assays. Multislice proton MRS imaging (MRSI) has previously detected more extensive brain abnormalities in X-ALD than conventional MRI, which has been suggested to predict impending demyelination. However, the significance of these changes is unclear. OBJECTIVE: The purpose of this study was to determine the long-term sensitivity and specificity of MRSI for disease progression in X-ALD. METHODS: Twenty-five patients with X-ALD were investigated (average age, 15 years; range, 2-43 years) with MRI and proton MRSI at baseline and follow-up MRI over a mean period of 3.5 years. Eight patients had normal MRI findings at baseline and on follow-up (noncerebral group), 11 had abnormal MRI at baseline and no change on follow-up (cerebral nonprogressive group), and 6 had progressive MRI abnormalities (cerebral progressive group). On MRSI, voxels were analyzed in the normal MRI-appearing perilesional white matter, or in the corresponding area in the noncerebral group. RESULTS: The concentration ratio of N-acetylaspartate (NAA) to choline was the most sensitive indicator of disease progression. The average NAA/choline ratio was 5.99 for the noncerebral group, 5.75 for the cerebral nonprogressive group, and 3.74 for the cerebral progressive group (p = 0.002). At a cut-off point of 5.0, the NAA/choline ratio predicted disease progression in all patients with six cerebral progressive disease (sensitivity 100%). The specificity was 83%, the positive predictive value was 66%, and the negative predictive value was 100%. CONCLUSIONS: Multislice proton MRS imaging is able to identify impending or beginning degeneration in white matter that still appears normal on conventional MRI. Multislice proton MRSI may be a suitable technique for the prediction of lesion progression on MRI in X-linked adrenoleukodystrophy.

ABCD1 mutations and the X-linked adrenoleukodystrophy mutation database: role in diagnosis and clinical correlations.

X-linked adrenoleukodystrophy (X-ALD) is caused by mutations in the ABCD1 gene, which encodes a peroxisomal ABC half-transporter (ALDP) involved in the import of very long-chain fatty acids (VLCFA) into the peroxisome. The disease is characterized by a striking and unpredictable variation in phenotypic expression. Phenotypes include the rapidly progressive childhood cerebral form (CCALD), the milder adult form, adrenomyeloneuropathy (AMN), and variants without neurologic involvement. There is no apparent correlation between genotype and phenotype. In males, unambiguous diagnosis can be achieved by demonstration of elevated levels of VLCFA in plasma. In 15 to 20% of obligate heterozygotes, however, test results are false-negative. Therefore, mutation analysis is the only reliable method for the identification of heterozygotes. Since most X-ALD kindreds have a unique mutation, a great number of mutations have been identified in the ABCD1 gene in the last seven years. In order to catalog and facilitate the analysis of these mutations, we have established a mutation database for X-ALD ( http://www.x-ald.nl). In this review we report a detailed analysis of all 406 X-ALD mutations currently included in the database. Also, we present 47 novel mutations. In addition, we review the various X-ALD phenotypes, the different diagnostic tools, and the need for extended family screening for the identification of new patients.

MPDU1 mutations underlie a novel human congenital disorder of glycosylation, designated type If.

Deficiencies in the pathway of N-glycan biosynthesis lead to severe multisystem diseases, known as congenital disorders of glycosylation (CDG). The clinical appearance of CDG is variable, and different types can be distinguished according to the gene that is altered. In this report, we describe the molecular basis of a novel type of the disease in three unrelated patients diagnosed with CDG-I. Serum transferrin was hypoglycosylated and patients' fibroblasts accumulated incomplete lipid-linked oligosaccharide precursors for N-linked protein glycosylation. Transfer of incomplete oligosaccharides to protein was detected. Sequence analysis of the Lec35/MPDU1 gene, known to be involved in the use of dolichylphosphomannose and dolichylphosphoglucose, revealed mutations in all three patients. Retroviral-based expression of the normal Lec35 cDNA in primary fibroblasts of patients restored normal lipid-linked oligosaccharide biosynthesis. We concluded that mutations in the Lec35/MPDU1 gene cause CDG. This novel type was termed CDG-If.

Peroxisomal disorders.

Peroxisomes are membrane-bound subcellular organelles that are involved in a variety of cellular functions. Disorders of peroxisomes, either in their assembly or single enzyme deficiencies, manifest themselves in the nervous system both in development and later in life. Most peroxisomal matrix proteins are targeted using one of the targeting sequences, whereas integral peroxisomal membrane proteins employ a different method. Peroxisomal importation is unique, allowing the importation of oligomerized proteins, and uses a specific extended shuttle system of receptor and cargo. The understanding of peroxisomal assembly is important because peroxisomal biogenesis disorders such as Zellweger syndrome result from these defects, and the resulting failure causes widespread deficiencies in peroxisomal biochemical function. X-linked adrenoleukodystrophy, representing the other group of peroxisomal disorders, is caused by the lack of the adrenoleukodystrophy protein, with an accumulation of very long chain fatty acids. New information on clinical incidence, phenotypic variability, and pathogenesis is becoming available and will have implications for possible therapies.