A new GNPAT variant of foetal rhizomelic chondrodysplasia punctata

Background

Rhizomelic chondrodysplasia punctata (RCDP) is a clinical entity resulting from defects of peroxisomal metabolism whose clinical phenotype is characterized by rhizomelia, calcified foci in periarticular cartilage, coronal lesions of vertebral bodies, cataracts and severe cognitive delay. Usually, survival does not exceed the first decade of life. Transmission is autosomal recessive and is related to mutations in the PEX7, GNPAT or AGPS.

Methods

A detailed description of the prenatal ultrasound signs of RCDP found in two successive pregnancies in a consanguineous couple is reported. Molecular genetic investigations included the study of the coding regions and the exon–intron junctions of the GNPAT (high‐throughput amplification and sequencing performed with Roche NimbleGen SeqCap Target kit on Illumina platform); the confirmation test was carried out by amplification and Sanger sequencing with automatic capillary sequencer.

Results

In addition to the typical prenatal ultrasound signs described in the literature in association with RCDP, the presence of prefrontal oedema, never previously described, has been detected in both pregnancies. Moreover, genetic investigations have found a new splicing variant c.924+1G>A of the homozygous GNPAT.

Conclusion

The role of mutation in the GNPAT suggests a likely association with the clinical phenotype.

The type-2 peroxisomal targeting signal

The type-2 peroxisomal targeting signal (PTS2) is one of two peptide motifs destining soluble proteins for peroxisomes. This signal acts as amphiphilic α-helix exposing the side chains of all conserved residues to the same side. PTS2 motifs are recognized by a bipartite protein complex consisting of the receptor PEX7 and a co-receptor. Cargo-loaded receptor complexes are translocated across the peroxisomal membrane by a transient pore and inside peroxisomes, cargo proteins are released and processed in many, but not all species. The components of the bipartite receptor are re-exported into the cytosol by a ubiquitin-mediated and ATP-driven export mechanism. Structurally, PTS2 motifs resemble other N-terminal targeting signals, whereas the functional relation to the second peroxisomal targeting signal (PTS1) is unclear. Although only a few PTS2-carrying proteins are known in humans, subjects lacking a functional import mechanism for these proteins suffer from the severe inherited disease rhizomelic chondrodysplasia punctata.

Cervical Spine Deformities in Children With Rhizomelic Chondrodysplasia Punctata

BACKGROUND

Cervical spine deformity in rhizomelic chondrodysplasia punctata (RCDP) has been described with different findings reported in the literature. However, available literature provides limited data from a few cases with magnetic resonance imaging (MRI) of the cervical spine. Our report describes the MRI findings in a group of children with RCDP, aiming to reach a better understanding of this pathology.

METHODS

An Institutional Review Board-approved RCDP Registry was created at our institution with the goal of identifying pertinent medical issues over the lifespan of individuals with RCDP. Records of children within the registry were evaluated, and magnetic resonance images obtained between 2004 and 2015, were available for review. The levels of spinal canal stenosis were recorded and the severity of the stenosis was decided based on adults' parameters. Cord compression and myelomalacia were confirmed on the axial images. Sagittal lumbar spine magnetic resonance images were also evaluated when available, and the presence of tethered cord and fatty filum was recorded.

RESULTS

Twenty-six children (15 boys and 11 girls) were identified in the RCDP Registry. Eleven children (6 boys and 5 girls) had sagittal MRI of the cervical spine available for review. Age at the time of MRI study was variable (1 wk to 32 mo). All patients except 1 had stenosis of the cervical spinal canal. Myelomalacia of the cord was noted only in this patient.

CONCLUSIONS

This study suggests that, in children with RCDP, cervical spinal stenosis and cord compression are a real risk, and children with this diagnosis should have monitoring for these issues. Tethered cord is also a possible finding that needs to be evaluated. Full sagittal spine MRI is necessary to detect the possible deformities at the cervical and lumbar levels.

Peripheral nervous system plasmalogens regulate Schwann cell differentiation and myelination

Rhizomelic chondrodysplasia punctata (RCDP) is a developmental disorder characterized by hypotonia, cataracts, abnormal ossification, impaired motor development, and intellectual disability. The underlying etiology of RCDP is a deficiency in the biosynthesis of ether phospholipids, of which plasmalogens are the most abundant form in nervous tissue and myelin; however, the role of plasmalogens in the peripheral nervous system is poorly defined. Here, we used mouse models of RCDP and analyzed the consequence of plasmalogen deficiency in peripheral nerves. We determined that plasmalogens are crucial for Schwann cell development and differentiation and that plasmalogen defects impaired radial sorting, myelination, and myelin structure. Plasmalogen insufficiency resulted in defective protein kinase B (AKT) phosphorylation and subsequent signaling, causing overt activation of glycogen synthase kinase 3β (GSK3β) in nerves of mutant mice. Treatment with GSK3β inhibitors, lithium, or 4-benzyl-2-methyl-1,2,4-thiadiazolidine-3,5-dione (TDZD-8) restored Schwann cell defects, effectively bypassing plasmalogen deficiency. Our results demonstrate the requirement of plasmalogens for the correct and timely differentiation of Schwann cells and for the process of myelination. In addition, these studies identify a mechanism by which the lack of a membrane phospholipid causes neuropathology, implicating plasmalogens as regulators of membrane and cell signaling.

Cervical spine stenosis in chondrodysplasia punctata

Chondrodysplasia punctata (CDP) is a rare skeletal dysplasia characterized by stippled epiphyses during infancy. The frequency is probably underdiagnosed because of the large heterogeneity in this group. Many genotypic variations exist. Although cervical instability is commonly seen in many skeletal dysplasias, cervical spine stenosis associated with CDP is very rare. We report a boy with phenotypic features of brachytelephalangic chondrodysplasia punctata (BCDP) who had severe cervical spine stenosis successfully corrected by vertebrectomies of C6 and C7 with a fibular strut graft. We discuss the significance of this association.

Neuroimaging features in a neonate with rhizomelic chondrodysplasia punctata

Rhizomelic chondrodysplasia punctata is a rare genetic disorder of peroxisomal metabolism that is characterized clinically by shortening of the proximal limbs, cataracts, a characteristic facial appearance, failure to thrive, and psychomotor retardation. This report describes a newborn with a severe phenotype whose neuroimaging showed pachygyria-polymicrogyria, severe spinal stenosis causing compression of the cervical cord and brainstem, and tethering of the spinal cord. Imaging of the brain and spinal cord in patients with this disorder may aid prognosis and guide management decisions.

The crucial step in ether phospholipid biosynthesis: structural basis of a noncanonical reaction associated with a peroxisomal disorder

Ether phospholipids are essential constituents of eukaryotic cell membranes. Rhizomelic chondrodysplasia punctata type 3 is a severe peroxisomal disorder caused by inborn deficiency of alkyldihydroxyacetonephosphate synthase (ADPS). The enzyme carries out the most characteristic step in ether phospholipid biosynthesis: formation of the ether bond. The crystal structure of ADPS from Dictyostelium discoideum shows a fatty-alcohol molecule bound in a narrow hydrophobic tunnel, specific for aliphatic chains of 16 carbons. Access to the tunnel is controlled by a flexible loop and a gating helix at the protein-membrane interface. Structural and mutagenesis investigations identify a cluster of hydrophilic catalytic residues, including an essential tyrosine, possibly involved in substrate proton abstraction, and the arginine that is mutated in ADPS-deficient patients. We propose that ether bond formation might be orchestrated through a covalent imine intermediate with the flavin, accounting for the noncanonical employment of a flavin cofactor in a nonredox reaction.

MRI of the brain and cervical spinal cord in rhizomelic chondrodysplasia punctata

BACKGROUND

The classic rhizomelic chondrodysplasia punctata (RCDP) phenotype involves a typical facial appearance, cataracts, skeletal dysplasia causing disproportionate somatic growth failure, microcephaly, and severe psychomotor defects. Biochemical abnormalities include impaired plasmalogen biosynthesis in all forms of RCDP and accumulation of phytanic acid in RCDP type 1. A subset of patients has a milder clinical and biochemical phenotype, with less severe neurologic impairment and an incomplete deficiency in plasmalogens. The impact of plasmalogen deficiency on neurologic function is severe, causing spasticity and mental defects, but its pathomechanism is still unknown. The authors specifically focused on myelination because myelin is rich in ethanolamine plasmalogens.

OBJECTIVE

To define the neuroimaging characteristics of the genetic peroxisomal disorder RCDP.

METHODS

Twenty-one MR images of the brain and cervical spine of 11 patients were evaluated and correlated with neurologic and biochemical profiles.

RESULTS

No abnormalities on MRI were seen in the patients with a mild phenotype of RCDP, whereas delayed myelination, ventricular enlargement and increased subarachnoidal spaces, supratentorial myelin abnormalities, and cerebellar atrophy were observed in patients with the severe phenotype of both RCDP type 1 and 3. The severity of both the MRI abnormalities and the clinical phenotype is correlated with the plasmalogen level.

CONCLUSIONS

The severe phenotype of rhizomelic chondrodysplasia punctata (RCDP) is accompanied by a specific pattern of both developmental and regressive MRI abnormalities. Plasmalogen levels seem to play an important role in the pathophysiology of CNS abnormalities in RCDP. Increased phytanic acid appears not to be the cause of cerebellar atrophy.

Multivoxel magnetic resonance spectroscopy in a rhizomelic chondrodysplasia punctata case

A case of a 5-day-old newborn with rhizomelic chondrodysplasia punctata was investigated with multivoxel magnetic resonance spectroscopy, including chemical shift imaging maps, which disclosed a decrease in the choline peak and the choline signal intensity, respectively, in the right cerebral hemisphere. This is the second report of multivoxel magnetic resonance spectroscopy examination of the brain associated with rhizomelic chondrodysplasia punctata in the literature. Multivoxel magnetic resonance spectroscopy with chemical shift imaging maps has the advantage of obtaining more information in a short period of time, which shortens the duration of anesthesia and its associated risks and complications. We suggest that future efforts be directed to evaluating such patients with multivoxel magnetic resonance spectroscopy instead of single-voxel magnetic resonance spectroscopy.

Impaired neuronal migration and endochondral ossification in Pex7 knockout mice: a model for rhizomelic chondrodysplasia punctata

Rhizomelic chondrodysplasia punctata is a human autosomal recessive disorder characterized by skeletal, eye and brain abnormalities. The disorder is caused by mutations in the PEX7 gene, which encodes the receptor for a class of peroxisomal matrix enzymes. We describe the generation and characterization of a Pex7 mouse knockout (Pex7(-/-)). Pex7(-/-) mice are born severely hypotonic and have a growth impairment. Mortality in Pex7(-/-) mice is highest in the perinatal period although some Pex7(-/-) mice survived beyond 18 months. Biochemically Pex7(-/-) mice display the abnormalities related to a Pex7 deficiency, i.e. a severe depletion of plasmalogens, impaired alpha-oxidation of phytanic acid and impaired beta-oxidation of very-long-chain fatty acids. In the intermediate zone of the developing cerebral cortex Pex7(-/-) mice have an increase in neuronal density. In vivo neuronal birthdating revealed that Pex7(-/-) mice have a delay in neuronal migration. Analysis of bone ossification in newborn Pex7(-/-) mice revealed a defect in ossification of distal bone elements of the limbs as well as parts of the skull and vertebrae. These findings demonstrate that Pex7 knockout mice provide an important model to study the role of peroxisomal functioning in the pathogenesis of the human disorder.

[Case report: Rhizomelic chondrodysplasia punctata and foramen magnum stenosis in a newborn]

Chondrodysplasia punctata is a peroxisomal disorder which is a form of multiple epiphyseal dysplasia. It is characterized by calcifications of unossified cartilaginous epiphyseal centers during the first year of life. Severe autosomal recessive rhisomelic form shows bilateral proximal shortening of the upper and lower limbs with punctate epiphyseal calcifications. We report radiological findings of a patient with rhisomelic chondrodysplasia punctata. Magnetic resonance imaging showed foramen magnum stenosis that caused spinal cord compression.

Lethal non-rhizomelic dysplasia epiphysealis punctata

We describe two new cases of a rare form of lethal chondrodysplasia punctata (so-called X-linked dominant, non-rhizomelic form), a condition characterized by widespread multicentric stippled calcifications of the cartilaginous parts of the long bones, spine, ribs and flat bones. The mother of one of the patients had bone dysplasia consistent with the X-linked dominant form of chondrodysplasia punctata. We suggest that a skeletal survey, including lateral view of the spine, together with biochemical studies of peroxisomal status are indicated in all newborns with severe, unusual forms of chondrodysplasia punctata. In this way, accurate categorization of the lethal, non-rhizomelic types of this condition will be facilitated.

Mutational spectrum in the PEX7 gene and functional analysis of mutant alleles in 78 patients with rhizomelic chondrodysplasia punctata type 1

Rhizomelic chondrodysplasia punctata (RCDP) is a genetically heterogeneous, autosomal recessive disorder of peroxisomal metabolism that is clinically characterized by symmetrical shortening of the proximal long bones, cataracts, periarticular calcifications, multiple joint contractures, and psychomotor retardation. Most patients with RCDP have mutations in the PEX7 gene encoding peroxin 7, the cytosolic PTS2-receptor protein required for targeting a subset of enzymes to peroxisomes. These enzymes are deficient in cells of patients with RCDP, because of their mislocalization to the cytoplasm. We report the mutational spectrum in the PEX7 gene of 78 patients (including five pairs of sibs) clinically and biochemically diagnosed with RCDP type I. We found 22 different mutations, including 18 novel ones. Furthermore, we show by functional analysis that disease severity correlates with PEX7 allele activity: expression of eight different alleles from patients with severe RCDP failed to restore the targeting defect in RCDP fibroblasts, whereas two alleles found only in patients with mild disease complemented the targeting defect upon overexpression. Surprisingly, one of the mild alleles comprises a duplication of nucleotides 45-52, which is predicted to lead to a frameshift at codon 17 and an absence of functional peroxin 7. The ability of this allele to complement the targeting defect in RCDP cells suggests that frame restoration occurs, resulting in full-length functional peroxin 7, which leads to amelioration of the predicted severe phenotype. This was confirmed in vitro by expression of the eight-nucleotide duplication-containing sequence fused in different reading frames to the coding sequence of firefly luciferase in COS cells.

Normal and defective neuronal membranes: structure and function: neuronal lesions in peroxisomal disorders

Neuronal involvement in the peroxisomal disorders is divided into two main groups: developmental and postdevelopmental or degenerative. In the former the major lesions are neuronal migration abnormalities, which vary from severe in the cerebro-hepato-renal (Zellweger) syndrome (ZS) to mild in neonatal adrenoleukodystrophy. More common, but much less severe, are defects in neuronal differentiation or terminal migration, particularly involving the inferior medullary olives. Ultrastructural and neurochemical observations in ZS suggest that the presence of abnormal cytosomes in migrating neurons and radial glia, probably the result of excessive very long chain fatty acids, are responsible in part for its major neocortical migration defect, parasylvian pachygyria-polymicrogyria. The postdevelopmental neuronal lesions involve specialized sensory neurons of the retina and the inner ear, resulting in atypical retinitis pigmentosa and its consequent visual defects and sensorineural hearing deficits. Neuronal atrophy and/or loss is seen in both the dorsal-root ganglia of adrenomyeloneuropathy and the atrophic cerebellum of rhizomelic chondodysplasia punctata. The underlying pathophysiology of these neuronal lesions is postulated to be caused by the incorporation of abnormal fatty acids into neuronal membranes, leading to an unresponsiveness to neurotrophic factors necessary for normal function and survival or to increased permeability of calcium channels and cell death.

PTS2 protein import into mammalian peroxisomes

Peroxisome targeting signal (PTS)2 directs proteins from their site of synthesis in the cytosol to the lumen of the peroxisome. Unlike PTS1 which is present in the great majority of peroxisomal matrix proteins and whose import mechanics have been dissected in considerable detail, PTS2 is a relatively rare topogenic signal whose import mechanisms are far less well understood. However, as is the case for PTS1 proteins, an inability to import PTS2 proteins leads to human disease. In this report, we describe the biochemical characterization of mammalian PTS2 protein import using a semi-permeabilized cell system. We show that a PTS2-containing reporter molecule is taken up by peroxisomes in a reaction that is time-, temperature-, ATP-, and cytosol-dependent. Furthermore, the import process is specific, saturable, and requires action of the chaperone Hsc70, the cochaperone Hsp40, and the peroxins Pex5p and Pex14p. We also demonstrate peroxisomal translocation of PTS2 reporter/antibody complexes confirming the import competence of higher order structures. Importantly, cultured fibroblasts from patients with the rhizomelic form of chondrodysplasia punctata (RCDP) which are deficient for the PTS2 receptor protein, Pex7p, are unable to import the PTS2 reporter in this assay. The ability to monitor PTS2 import in vitro will permit, for the first time, a detailed comparison of the biochemical properties of PTS1 and PTS2 protein import.

Cervical stenosis secondary to rhizomelic chondrodysplasia punctata

Rhizomelic chondrodysplasia punctata (RCDP) is a rare peroxisomal disorder leading to multiple developmental malformations, including skeletal deformity. Specifically, involvement of the vertebral bodies has been described. Presented here is a case of a two-year-old female child with RCDP leading to advanced cervical stenosis as detected on magnetic resonance imaging (MRI) studies of the cervical spine. The practicing clinician should be aware of the possibility of cervical stenosis secondary to RCDP and its impact on the management of the patient with this rare disease process.

Lethal form of chondrodysplasia punctata with normal plasmalogen and cholesterol biosynthesis

We present a male autopsied case of chondrodysplasia punctata with abnormal face, symmetrical proximal limb shortness, severe psychomotor developmental delay, respiratory muscle weakness, and death at the age of 2 years. Although his clinical manifestations were similar to those of rhizomelic chondrodysplasia punctata (RCDP), biochemical studies using skin fibroblasts did not document the peroxisomal dysfunction described in RCDP. In addition, the sterol profile, for which abnormalities have recently been reported in cases of X-linked dominant form chondrodysplasia punctata (CDPX2), was normal both in the liver and in the fibroblasts. This patient may represent a new lethal form of chondrodysplasia punctata.

Abnormal myelin formation in rhizomelic chondrodysplasia punctata type 2 (DHAPAT-deficiency)

The case of a Yemeni girl with isolated peroxisomal acyl-CoA:dihydroxyacetonephosphate acyltransferase (DHAPAT) deficiency is reported. She had rhizomelic chondrodysplasia punctata, microcephaly, failure to thrive, delayed motor and mental development, and spastic quadriplegia. Deficient de novo plasmalogen synthesis in her fibroblasts as a result of low DHAPAT activity was found, while her very-long-chain fatty acid profile, phytanic acid concentration, alkyl-dihydroxyacetonephosphate synthase (alkyl-DHAP synthase) activity, and peroxisomal 3-ketoacyl-CoA thiolase protein were normal. A mutation in her DHAPAT complementary DNA resulted in the substitution of an arginine residue in the protein at position 211 by a histidine (R211H). Magnetic resonance imaging showed abnormal white matter signal in the centrum semiovale involving the arcuate fibers, while the corpus callosum was normal. DHAPAT and alkyl-DHAP synthase initiate the synthesis of plasmalogens, which are major constituents of myelin phospholipids. The reported girl's abnormal formation of myelin is probably related to the inadequacy of plasmalogen biosynthesis, which is likely to be due to deficient DHAPAT activity.

Ether lipid biosynthesis: alkyl-dihydroxyacetonephosphate synthase protein deficiency leads to reduced dihydroxyacetonephosphate acyltransferase activities

Recent studies have indicated that two peroxisomal enzymes involved in ether lipid synthesis, i.e., dihydroxyacetonephosphate acyltransferase and alkyl-dihydroxyacetonephosphate synthase, are directed to peroxisomes by different targeting signals, i.e., peroxisomal targeting signal type 1 and type 2, respectively. In this study, we describe a new human fibroblast cell line in which alkyl-dihydroxyacetonephosphate synthase was found to be deficient both at the level of enzyme activity and enzyme protein. At the cDNA level, a 128 base pair deletion was found leading to a premature stop. Remarkably, dihydroxyacetonephosphate acyltransferase activity was strongly reduced to a level comparable to the activities measured in fibroblasts from patients affected by the classical form of rhizomelic chondrodysplasia punctata (caused by a defect in peroxisomal targeting signal type 2 import). Dihydroxyacetonephosphate acyltransferase activity was completely normal in another alkyl-dihydroxyacetonephosphate synthase activity-deficient patient. Fibroblasts from this patient showed normal levels of the synthase protein and inactivity results from a point mutation leading to an amino acid substitution. These results strongly suggest that the activity of dihydroxyacetonephosphate acyltransferase is dependent on the presence of alkyl-dihydroxyacetonephosphate synthase protein. This interpretation implies that the deficiency of dihydroxyacetonephosphate acyltransferase (targeted by a peroxisomal targeting signal type 1) in the classic form of rhizomelic chondrodysplasia punctata is a consequence of the absence of the alkyl-dihydroxyacetonephosphate synthase protein (targeted by a peroxisomal targeting signal type 2).

Cerebellar atrophy in chronic rhizomelic chondrodysplasia punctata: a potential role for phytanic acid and calcium in the death of its Purkinje cells

Cerebellar atrophy, consequent to the postdevelopmental degeneration and loss of Purkinje cells and granular neurons, has been identified in three patients with rhizomelic chondrodysplasia punctata (RCDP). Cerebellar atrophy in our two chronic patients was symmetrical, but the vermis and medial portions of both hemispheres, particularly the dorsal lobules, displayed more severe atrophy than the lateral hemispheres. The distal tips of folia showed the greatest neuronal loss. Residual Purkinje cells showed progressive degenerative changes that appeared to be due, in part, to their topography. The precise mode of death of Purkinje cells in RCDP has not been established, but it does not appear to be mediated by entrance into the cell cycle or by ubiquitination; however, alterations in intracellular calcium levels and mitochondria may be involved. Elevated serum/CSF phytanic acid, decreased levels of tissue plasmalogens and increased chronological age are believed to play synergistic pathogenetic roles in this lesion.

Prenatal diagnosis of rhizomelic chondrodysplasia punctata due to isolated alkyldihydroacetonephosphate acyltransferase synthase deficiency

Current practices in prenatal diagnosis of rhizomelic chondrodysplasia punctata (RCDP) are reviewed. A case is presented with a family having one daughter affected with RCDP due to alkyldihydroacetonephosphate acyltransferase synthase (DHAPAT synthase) deficiency, and three subsequent pregnancies. Biochemical test values are presented for the pregnancies and daughter. Post-mortem tests of one fetus of a terminated pregnancy showed that radiologic examination could not make the diagnosis of RCDP. We conclude that biochemical or molecular testing is necessary to accurately diagnose this type of RCDP prenatally.

Clinical approach to inherited peroxisomal disorders: a series of 27 patients

To illustrate the clinical and biochemical heterogeneity of peroxisomal disorders, we report our experience with 27 patients seen personally between 1982 and 1997. Twenty patients presented with a phenotype corresponding either to Zellweger syndrome, neonatal adrenoleukodystrophy, or infantile Refsum disease, 3 of whom had a peroxisomal disorder due to a single enzyme defect. One patient had a mild form of rhizomelic chondrodysplasia punctata, 1 had classic Refsum disease. Finally, 5 patients presented with clinical manifestations that were either unusually mild or completely atypical, and initially did not arouse suspicion of a peroxisomal disorder. They showed multiple defects of peroxisomal functions with one or several functions remaining intact, suggesting a peroxisome biogenesis disorder. The defect in peroxisome biogenesis was further characterized by variable expression in different tissues and/or individual cells in 5 patients. Studies restricted to fibroblasts failed to identify abnormalities in this group. We demonstrate that clinical manifestations of peroxisomal disorders may be very mild or completely atypical, and therefore, peroxisomal disorders should be considered in a variety of clinical settings. Furthermore, we suggest performing extensive peroxisomal investigations in every patient suspected of suffering from a peroxisomal disorder, even when the clinical presentation is typical.

Chondrodysplasia in Australian Dexter cattle

OBJECTIVE

To describe the occurrence of chondrodysplasia in Australian Dexter cattle.

DESIGN

A pathological and genetic case report.

PROCEDURE

Congenital lethal chondrodysplasia was studied in two female Dexter foetuses aborted mid to late gestation. Clinicopathological findings including histological changes in limb bones, and analysis of pedigree information were evaluated.

RESULTS

Characteristic features of congenital lethal chondrodysplasia (Dexter bulldog) include abortion, disproportionate dwarfism, a short vertebral column, marked micromelia, a relatively large head with retruded muzzle, cleft palate and protruding tongue and a large abdominal hernia. Histological changes in limb bones are consistent with failure of endochondral ossification. Dexter chondrodysplasia is considered to be inherited in an incompletely dominant manner with the homozygous form producing the congenital lethal condition. A preliminary minimum estimate of heterozygote frequency is 19% within the registered Australian Dexter herd, based on analysis of the contribution of three obligate heterozygotes whose semen has been widely used by artificial insemination in Australia.

CONCLUSION

Dexter chondrodysplasia is present in Australian cattle and further cases of the homozygous form, congenital lethal chondrodysplasia, are likely to occur.

RECOMMENDATION

It is requested that spleen and liver tissue from bulldog foetuses and blood from their parents be collected to assist research into Dexter chondrodysplasia.

Isolated dihydroxyacetonephosphate-acyl-transferase deficiency in rhizomelic chondrodysplasia punctata: clinical presentation, metabolic and histological findings

Rhizomelic chondrodysplasia punctata (RCDP) is clinically characterized by symmetrical shortening of the proximal limbs, contractures of joints, a characteristic dysmorphic face, and cataracts. In the classical form an impairment of several peroxisomal functions and enzymes (plasmalogen synthesis, phytanic acid oxidation, 3-oxoacyl-CoA thiolase) has been repeatedly shown. Recently a variant involving only the peroxisomal dihydroxyacetonephosphate acyltransferase (DHAP-AT) has been described. We present a patient with isolated DHAP-AT deficiency and all clinical, radiological and pathological features of classical RCDP. For the first time, microscopy and immunocytochemistry of hepatocytes could be performed.

CONCLUSION

In contrast to studies on classical rhizomelic chondrodysplasia punctata which have shown enlarged peroxisomes in numbers varying from hepatocyte to hepatocyte, the peroxisomes in our patient seem to be normal in size, number and shape.

Phytanic acid oxidation: normal activation and transport yet defective alpha-hydroxylation of phytanic acid in peroxisomes from Refsum disease and rhizomelic chondrodysplasia punctata

In humans the oxidation of phytanic acid is a peroxisomal function. To understand the possible mechanisms for the pathognomic accumulation of phytanic acid in plasma and body fluids of Refsum disease (RD) and rhizomelic chondrodysplasia punctata (RCDP), we investigated activities of various steps (activation, transport, and oxidation) in the metabolism of phytanic acid in peroxisomes isolated from cultured skin fibroblasts from control, RD, and RCDP subjects. Activation of phytanic acid was normal in peroxisomes from both RD and RCDP. Transport of phytanic acid or phytanoyl-CoA in the absence or presence of fatty acid activating cofactors (ATP, MgCl2, and CoASH) into peroxisomes isolated from RD and RCDP skin fibroblasts was also similar to that of peroxisomes from control fibroblasts. Defective oxidation of [(2,3)-3H]- or [1-14C]phytanic acid, or [1-14C]phytanoyl-CoA (substrate for the first step of alpha-oxidation) but normal oxidation of [1-14C] alpha-hydroxyphytanic acid (substrate for the second step of the alpha-oxidation pathway) in peroxisomes from RD clearly demonstrates that excessive accumulation of phytanic acid in plasma and body fluids of RD is due to the deficiency of phytanic acid alpha-hydroxylase in peroxisomes. However, in RCDP peroxisomes, in addition to deficient oxidation of [1-14C]phytanic acid or phytanoyl-CoA or [(2,3)-3H]phytanic acid, the oxidation of [1-14C] alpha-hydroxyphytanic acid was also deficient, indicating that in RCDP the activities both of alpha-hydroxylation of phytanic acid and decarboxylation of alpha-hydroxyphytanic acid are deficient. These observations indicate that peroxisomal membrane functions (phytanic acid activation and transport) in phytanic acid metabolism are normal in both RD and RCDP. The defect in RD is in the alpha-hydroxylation of phytanic acid; whereas in RCDP both alpha-hydroxylation of phytanic acid as well as decarboxylation of alpha-hydroxyphytanic acid are deficient.

Rhizomelic chondrodysplasia punctata: report of a case with review of the literature and correlation with other peroxisomal disorders

A 3-year-old girl with rhizomelic chondrodysplasia punctata (RCDP) had severe microcephaly but a normal gyral pattern, neuronal density, and cortical cytoarchitecture. The white matter was diffusely decreased in mass but normally myelinated. There was optic atrophy and cerebellar degeneration. Leukodystrophy in peroxisomal disorders is caused by elevated very long chain fatty acids. The absence of a fatty acid abnormality in RCDP explains the normal myelination. Cerebellar and retinal degeneration and possible stunted dendritogenesis may be due to plasmalogen deficiency, which is the most severe biochemical abnormality in RCDP.