A HaeIII RFLP in COL1A1

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Infantile phytanic acid storage disease, a disorder of peroxisome biogenesis: a case report

The infantile and classic forms of phytanic acid storage disease belong to the newly recognized group of peroxisomal disorders. In this paper we report the full clinical, morphological and biochemical results in a patient with infantile phytanic acid storage disease. The results indicate a generalized loss of peroxisomal functions due to a deficiency of peroxisomes as demonstrated in hepatocytes and cultured skin fibroblasts.

Markedly reduced activity of lysyl oxidase in skin and aorta from a patient with Menkes' disease showing unusually severe connective tissue manifestations

In Menkes' disease, a severe disturbance of copper handling appears to render copper unavailable for copper-requiring processes. We have measured the activity of lysyl oxidase, the copper-dependent enzyme that initiates the cross-linking of collagen and elastin, in extracts of skin and aorta obtained at autopsy from a patient with unusually marked connective tissue manifestations, and found it to be only 6-12% of normal, thus suggesting a basis for these alterations.

Collagen degradation in I-cells is normal

There is evidence that lysosomal proteases mediate the intracellular degradation of structurally abnormal collagen. I-Cell disease (Mucolipidosis II) is characterized by marked deficiency of many lysosomal hydrolases, including the collagenolytic enzyme cathepsin B. The experiments reported here tested the hypothesis that degradation of abnormal collagen would be severely impaired in I-cells. Skin fibroblasts from 3 patients with I-cell disease were incubated with and without cis-hydroxyproline, a proline analog that causes structural abnormalities in collagen, and [14C]proline. The amount of [14C]hydroxyproline in a low molecular weight fraction relative to total [14C]hydroxyproline was used as a measure of intracellular collagen degradation. Levels of degradation were significantly higher in I-cells exposed to cis-hydroxyproline than in cells incubated without the analog. Similar data were obtained for normal human fetal lung fibroblasts incubated under the same conditions. Degradation of [125I]-epidermal growth factor was used to assess the functionality of the lysosomal pathway for protein degradation, and it was much lower in I-cells than in normal cells. It can be concluded that a completely functional complement of lysosomal enzymes is not necessary for structurally abnormal collagen to be degraded intracellularly; the data suggest that a nonlysosomal pathway exists.

In vivo and in vitro noncovalent association of excised alpha 1 (I) amino-terminal propeptides with mutant pN alpha 2(I) collagen chains in native mutant collagen in a case of Ehlers-Danlos syndrome, type VII

The cause of the Ehlers-Danlos syndrome Type VII (EDS VII) is considered to be defective removal of the amino-terminal propeptide (N-propeptide) of Type I procollagen due to deficiency of procollagen N-proteinase, the enzyme responsible for the normal proteolytic excision of this precursor-specific domain. Molecules retaining the N-propeptide (pN-collagen molecules) are thought to cause defective fibrillogenesis and cross-linking which eventuate in dramatic joint laxity and joint dislocations, the clinical hallmark of this variety of EDS. Recent studies demonstrate that some EDS VII patients harbor small deletions of either the pro-alpha 1(I) or pro-alpha 2(I) chain of Type I procollagen. We have found an 18-amino acid deletion (due to exon outsplicing) in a mutant pro-alpha 2(I) chain from such a patient. The deleted peptide is the junctional segment (N-telopeptide) linking the alpha 2(I) N-propeptide and major triple helical domains; loss of this short segment results in union of these latter domains and produces a shortened pN alpha 2(I) chain. Directly extracted tissue collagen and pepsin-digested fibroblast collagen contain this mutant pN alpha 2(I) chain and normal alpha 1(I) chains, but not pN alpha 1(I) chains, indicating that the relatively larger alpha 1(I) N-propeptide is excised from the related alpha 1(I) chains. The fate of this alpha 1(I) N-propeptide was unclear and therefore whether or not the intact N-propeptide was, in fact, retained in native mutant collagen was also unclear. In this paper, we describe morphologic, chemical, and immunochemical studies which indicate that the alpha 1(I) N-propeptide is retained in noncovalent association with the mutant pN alpha 2(I) chain in native mutant collagen molecules both in vivo and in vitro. In both instances, the alpha 1(I) N-propeptides are proteolytically cleaved from the related alpha 1(I) chains. These data suggest that retention of a partially cleaved, but essentially intact N-propeptide in mutant collagen may play a role in the pathogenesis of this disease.

Brittle cornea syndrome: an heritable connective tissue disorder distinct from Ehlers-Danlos syndrome type VI and fragilitas oculi, with spontaneous perforations of the eye, blue sclerae, red hair, and normal collagen lysyl hydroxylation

We report a patient with the characteristic features of the brittle cornea syndrome, a rare, autosomal recessively inherited disorder, namely brittle corneae, blue sclerae, and red hair. The patient also showed joint hyperextensibility, a soft skin, and dysplastic auricles with unusually soft cartilage. Phenotypically, the disorder bears a certain resemblance to fragilitas oculi and the type VI (ocular) form of the Ehlers-Danlos syndrome, two conditions which are, themselves, not readily distinguishable. However, the hydroxylysine content of dermal collagen was normal, as was the activity of lysyl hydroxylase in cultured dermal fibroblasts, thus supporting the distinction of the brittle cornea syndrome as an independent entity. No abnormality was discernible in types I or III collagens synthesised by cultured fibroblasts, but electron microscopy revealed dramatic ultrastructural alterations in dermis in that distributed over its whole thickness were 20-60 microns wide "holes" or fibre-free spaces, filled with an amorphous material.

Radiological "metamorphosis" in a patient with severe congenital osteogenesis imperfecta

Congenital osteogenesis imperfecta (OI) was diagnosed by ultrasound in a 31-week-old fetus, and the diagnosis confirmed after delivery by caesarean section at week 36. The baby survived the neonatal period, but failed to thrive, had recurrent respiratory infections and ultimately died at 8 months. Cultured fibroblasts synthesized both normal type I collagen and unstable type I collagen harbouring a structural defect in the alpha 1 (I) cyanogen bromide-derived peptide number 8 (CB8) region of the molecule, indicating a heterozygous dominant mutation. At birth, the radiological picture was that of the "thin bone"-type of congenital OI (OI type IIB/III in the Sillence classification); at the age of 12 weeks ribs and long bones had undergone a marked expansion giving a very different picture, that of the "thick bone"-type congenital OI (OI type IIA). The mechanism responsible for this change in bone structure is not known, but fractures and callus formation are unlikely to be the only factors. Caution is needed in the interpretation of radiographs of newborns with OI for prognostic or genetic purposes.

Missense mutations associated with RFLP haplotypes 1 and 4 of the human phenylalanine hydroxylase gene

We report missense mutations associated with haplotype 1 and haplotype 4 alleles of the human phenylalanine hydroxylase (PAH) gene. Individual exon-containing regions were amplified by polymerase chain reaction from genomic DNA of a PKU patient who was a haplotype 1/4 compound heterozygote. The amplified DNA fragments were subcloned into M13 for sequence analysis. Missense mutations were observed in exons 5 and 7, resulting in the substitution of Arg by Gln at residues 158 and 261 of the enzyme, respectively. Expression analysis in heterozygous mammalian cells after site-directed mutagenesis demonstrated that the Arg158-to-Gln158 mutation is a PKU mutation, whereas the Arg261-to-Gln261 mutation is apparently silent in the assay system. Hybridization analysis using allele-specific oligonucleotide probes demonstrated that the Arg158-to-Gln158 mutation is present in two of six mutant haplotype 4 alleles among the Swiss and constitutes about 40% of all mutant haplotype 4 alleles in the European population. The mutation is not present in normal alleles or in any mutant alleles of other haplotypes. The results provide conclusive evidence that there is linkage disequilibrium between mutation and haplotype in the PAH gene and that multiple mutations have occurred in the PAH gene of a prevalent haplotype among Caucasians.

Temperature-dependent expression of a collagen splicing defect in the fibroblasts of a patient with Ehlers-Danlos syndrome type VII

In this article we report the characterization of the molecular lesion in a patient with Ehlers-Danlos syndrome Type VII and provide evidence that a de novo substitution of the last nucleotide of exon 6 in one allele of the pro-alpha 2(I) collagen gene produces normally spliced mRNA and transcripts from which exon 6 sequences have been outspliced as well. Unexpectedly, the expression of the alternative splicing was found to be temperature-dependent, for missplicing in cellula is effectively abolished at 31 degrees C and gradually increases to 100% at 39 degrees C. In contrast, in a similar patient harboring a substitution in the obligatory GT dinucleotide of the 5' splice site of intron 6, complete outsplicing of exon 6 sequences was found at all temperatures.

Hyperprolinaemia type I and white matter disease: coincidence or causal relationship?

We describe a 10-year-old boy with hyperprolinaemia type I and severe neurological abnormalities (mental retardation, cerebral palsy, epilepsy, nystagmus). Magnetic resonance imaging showed diffuse white matter involvement and electroretinography confirmed tapetoretinal degeneration. In view of reports in the literature, hyperprolinaemia type I may not be a benign condition, as usually assumed, but may lead to marked neurological abnormalities, particularly in affected males.

Ehlers-Danlos syndrome type IV: a subset of patients distinguished by low serum levels of the amino-terminal propeptide of type III procollagen

Serum levels of procollagen type III aminopropeptide (P-III-NP), a peptide released during conversion of type III procollagen to collagen, were abnormally low in six of 10 patients with Ehlers-Danlos syndrome (EDS) type IV (arterial-ecchymotic type) and low-normal in 4. The serum P-III-NP levels correlated with the amount of type III procollagen secreted by the patients' cultured fibroblasts. Serum P-III-NP determination is a simple test that identifies a major subgroup of patients with this life-threatening, dominantly inherited connective tissue disorder and may be especially helpful in making the diagnosis in children.

Clinical variability of osteogenesis imperfecta linked to COL1A2 and associated with a structural defect in the type I collagen molecule

We report a family in which dominant osteogenesis imperfecta segregates with a COL1A2 haplotype and is associated with a structural defect in the helical region of the type I procollagen molecule. All affected subjects had short stature, dentinogenesis imperfecta, and myopia; however, great differences were observed in the number of fractures and in the degree of bone deformity. Identical biochemical changes were found in the type I collagen molecules synthesised by fibroblasts of subjects with severe or minimal bone fragility. These results confirm that mutations in the triple helical region of alpha 2(I) chains produce a milder phenotype than analogous mutations in the alpha 1(I) chains, but indicate that, in addition to defects in the type I collagen molecule, other factors may modulate the degree of bone involvement in osteogenesis imperfecta.

Patients with hereditary fructose intolerance have normal erythrocyte aldolase activity

Erythrocyte fructose 1,6-bisphosphate aldolase (EC 4.1.2.13) activity was measured in eight children and adults with hereditary fructose intolerance and found to be normal when compared with eleven healthy controls. Therefore, hereditary fructose intolerance cannot be diagnosed by assaying red blood cell aldolase.

Molecular defects of type III procollagen in Ehlers-Danlos syndrome type IV

Fibroblasts from most patients with Ehlers-Danlos syndrome (EDS) type IV, a disorder characterized by fragility of skin, blood vessels, and internal organs, secrete reduced amounts of type III procollagen. In 7 of 8 cell strains analyzed, we found evidence of structural defects in half of the type III procollagen chains synthesized, such as deletions or bona fide amino acid substitutions, which cause delayed formation and destabilization of the collagen triple helix and, as a consequence, reduced secretion of the molecule. The data suggest that EDS type IV is often caused by heterozygosity for mutations at the COL3A1 locus, which affect the structure of type III procollagen. The triple-helical region of the molecule, like the homologous region of type I procollagen, appears to be particularly vulnerable.

Haplotype distribution of the human phenylalanine hydroxylase locus in Scotland and Switzerland

RFLP haplotypes at the phenylalanine hydroxylase (PAH) locus were determined in 45 nuclear Caucasian families from Switzerland and Scotland. The RFLPs at the PAH locus are highly informative, and prenatal diagnosis is possible in 85% of the families studied. The data were combined with the profiles previously observed in the Danish population, in order to study the variation in RFLP haplotype distribution among European populations. A total of 22 different haplotypes were observed in Denmark, Switzerland, and Scotland. Fifteen and 19 haplotypes are associated with the normal (non-PKU) and with the mutant chromosomes, respectively. The haplotype distribution and the allele frequency of normal chromosomes remain constant between Denmark, Switzerland, and Scotland. However, both the haplotype distribution and allele frequencies of mutant chromosomes show significant variation between the three countries. Our results suggest there may be additional mutations in the PAH gene that cause PKU.

Ehlers-Danlos syndrome type VI with normal lysyl hydroxylase activity cannot be explained by a defect in cellular uptake of ascorbic acid

The uptake of ascorbic acid by cultured skin fibroblasts from two siblings with Ehlers-Danlos syndrome type VI, in extracts of which there is no deficit in lysyl hydroxylase activity, was found to be normal. Decreased availability of ascorbic acid to lysyl hydroxylase in cellula cannot, therefore, provide an explanation for the disorder in these patients, the cause of which remains obscure.

Decreased thermal denaturation temperature of osteogenesis imperfecta mutant collagen is independent of post-translational overmodifications of lysine and hydroxylysine

Fibroblasts from many patients with osteogenesis imperfecta (OI) synthesize and secrete Type I collagen which is both overmodified and exhibits a decreased thermal denaturation temperature. We have examined the relationship between overmodification and decreased melting temperature in several favorable OI mutants by selectively inhibiting lysyl hydroxylase activity with the drug Minoxidil and comparing the melting profiles of the resultant undermodified collagen with untreated control. Minoxidil treatment causes an appreciable decrease in hydroxylysine with compensatory increases in lysine content, and the delayed sodium dodecyl sulfate-polyacrylamide gel electrophoretic mobility of the overmodified collagen chains becomes normal. However, the decreased melting temperature was unchanged from untreated OI control. When unhydroxylated collagen produced by normal control and OI fibroblasts incubated with alpha,alpha'-dipyridyl was examined, mutant OI molecules melted at a lower temperature than control. These data indicate that the decreased thermal denaturation temperature of OI mutant collagen is independent of post-translational overmodification of lysine or hydroxylysine. Presumably, substitutions for glycine in the Gly-X-Y structural motif distort the helix and produce lower melting temperatures by presently unknown mechanisms.