D. M. Broadhead

Peroxisomal Enzyme Deficiency in X-linked Dominant Conradi—Hünermann Syndrome

The X-linked dominant Conradi—Hunermann syndrome (CHS-XD, McKusick 30295) is characterized by ichthyosiform erythroderma at birth giving way to whorled areas of hyperkeratosis, streaky follicular atrophoderma, cicatricial alopecia and coarse lustreless hair. The facies typically shows frontal bossing, a flattened nasal bridge and malar hypoplasia. Cataracts are common. Skeletal abnormalities include the transient punctate epiphyseal calcifications, asymmetric limb shortening and short stature. According to Happle (1981), CHS-XD can be readily distinguished from an autosomal dominant form of the Conradi—Hunermann syndrome (CHS-AD, McKusick 11865) because the latter does not produce whorled/streaky skin lesions or cataracts. Differentiation between CHS-XD and autosomal recessive rhizomelic chondrodysplasia punctata (RCP, McKusick 21510) presents no serious problem: patients with RCP have severe, symmetrical proximal limb shortening, marked psychomotor retardation, mild ichthyotic skin changes and they rarely survive beyond 2 years of age.

Prenatal Diagnosis of Inherited Metabolic Disease by Chorionic Villus Analysis: The Edinburgh Experience

Prenatal diagnosis of inherited metabolic disease is possible when suitable samples of fetal material are available and when these samples express a clear biochemical abnormality that is specific to that disorder. In the past, tests have been carried out by enzyme assay on cultured amniotic fluid cells and/or analysis of amniotic fluid for metabolites. These tests, carried out late into pregnancy (16 weeks plus), cause much anxiety and added risks to mothers. With the advent of first trimester chorionic villus sampling, tests may now be carried out directly on chorionic villus samples (CVS) with results available in a matter of days (Poenaru, 1987; Sachs et al., 1988). The advantages to those at risk are obvious but like many new techniques specific problems may arise.

Steroid sulphatase and arylsulphatase C in X-linked ichthyosis

The skin disorder, X-linked ichthyosis, has been shown (Shapiro et al., 1977) to be associated with a deficiency of steroid sulphatase (EC 3.1.6.2.), and arylsutphatase C, measured using artificial substrates, is also deficient. Patients usually present at term, not necessarily with ichthyosis, but with delayed onset of labour in the mother. Non-inactivation of the steroid sulphatase/arylsulphatase C locus has been reported (Shapiro et al., 1979). This might be expected to give rise to a two-fold difference in activity between normal females and normal males. It is important, therefore, to establish normal ranges of steroid sulphatase and arylsulphatase C for males and females.

Comparison of the substrate 4-Methylumbelliferyl-α-l-iduronide with phenyl-α-l-iduronide for the diagnosis of Hurler's disease in cultured cells

Abstract4-Methylumbelliferyl-α-l-iduronide provided a more sensitive method than phenyl-α-l-iduronide for the estimation of α-l-iduronidase in cultured cells and could be used to diagnose Hurlers disease. The 4-methylumbelliferyl derivative was no more useful than the phenyl derivative for the detection of heterozygotes. All ten lysosomal enzymes tested could be used as reference enzymes when cell extracts were prepared by freeze/thawing in distilled water, but onlyN-acetyl-β-d-glucosaminidase could be used for extracts prepared by freeze/thawing in formate buffer pH 3.5 containing 150 mmol/l sodium chloride.

α-Glucosidase in Pompe's disease

Isoelectric precipitation at pH 5.0 and the use of the inhibitors, turanose, maltose and citrate, enabled the diagnosis of Pompes disease to be made in dextran-isolated leucocytes using 4-methylumbelliferyl-α-D-gluco-pyranoside as substrate. These techniques were unnecessary with lymphocytes as the deficiency of acid α-glucosidase could be shown directly.

Dihydroxyacetone Phosphate Acyltransferase Deficiency in Peroxisomal Disorders

There is much current interest in disorders of peroxisomal function and until recently little was known of the biochemical basis of these diseases. In patients such as those with Zellweger syndrome (McKusick 21410) where there is a generalized peroxisomal disturbance, a number of biochemical functions are impaired (Schutgens et al., 1986). Recognition of these defects may assist in diagnosis. These biochemical defects include accumulations of very long chain fatty acids, bile acid intermediates, phytanic acid, pipecolic acid and dicarboxylic acids, all of which appear to be normally oxidized in peroxisomes. Furthermore, there is a reduction in the level of certain plasmalogens (Heymans et al., 1984), the synthesis of which is dependent on two peroxisomal enzymes, acyl-CoA: dihydroxyacetone phosphate acyl transferase (DHAP-AT) and alkyl dihydroxyacetone phosphate synthase. Deficiencies of each of these activities have been reported (Schutgens et al., 1984; Datta et al., 1984) in Zellweger syndrome. Deficiency of DHAP-AT activity has also been reported in infantile Refsum disease and neonatal adrenoleukodystrophy (McKusick 20237) as well as in the rhizomelic form of chondrodysplasia punctata (McKusick 21510) where peroxisomes may be present. In response to the need for a simple but reliable preand postnatal diagnostic test for these disorders, we have studied DHAP-AT activity in cultured fibroblasts, blood thrombocytes and leukocytes from such patients and report our findings here.

Acid Esterase Deficiency: Comparison of Biochemical Findings in Infantile and Adult Forms

A deficiency of lysosomal acid esterase activity in humans usually results in one of two phenotypically distinct storage disorders (Assmann and Fredrickson, 1983). In Wolman’s disease (McKusick 27800) the course is rapid, resulting in death in infancy whereas cholesterol ester storage disease (CESD; McKusick 21500) is relatively benign and patients usually survive well into adulthood. These disorders are relatively rare and few comparative biochemical studies have been reported. In this report, three patients, two with Wolman’s disease and one with CESD, have been studied in an attempt to identify a biochemical basis for their phenotypic expression.

Diagnosis of Gaucher's disease in cultured skin fibroblasts and leucocytes.

Washing skin fibroblasts or leucocytes in 0.25 mol/l sucrose increases the activity ofβ-glucosidase at acid pH. This effect is primarily due to removal of low levels of sodium chloride, which inhibit acidβ-glucosidase. A secondary factor for skin fibroblasts is the removal of residual phosphate buffer pH 7.3 used to wash the cells following trypsinization. As theβ-glucosidase activity of water-lysed leucocytes is higher at acid pH than that of a saline suspension of leucocytes, the former are better for the diagnosis of Gauchers disease. However, more reliable results still may be obtained by assay of this enzyme in cultured skin fibroblasts.

Diagnosis of Hexosaminidase a Deficiency with Sulphated Substrate: Evidence for an alpha-Locus Genetic Compound in a Tay-Sachs Variant

Two major forms of lysosomal β-hexosaminidase activity exist in human tissues and cells. The A form, containing ∝β subunits, has an acid pi, is heat labile and specifically hydrolyses GM2-ganglioside. The B component, containing ββ subunits, has a basic pi, is relatively heat stable and has a broader substrate specificity. In vitro, both enzymes readily hydrolyse a number of artificial conjugates of N-acetylglucosamine and N-acetylgalactosamine. The fluorogenic substrate, 4-methylumbelliferyl-2-acetamido-2-deoxyβ- D-glucopyranoside (4MU-GlcNAc) has for some time been used to assay β-hexosaminidase activities. However, sulphation of this substrate (or the p-nitrophenol derivative) in the 6-position of the amino sugar, produces a substrate which is specific for β-hexosaminidase A but not the B isoenzyme (Kresse et al 1981; Inui and Wenger 1984; Bayleran et al 1984). This substrate therefore provides a simple and sensitive one step assay of β-hexosaminidase A activity and recognition of its deficiency in Tay-Sachs disease.