Presymptomatic neuropsychological impairment in Huntington's disease

Ten asymptomatic individuals at risk for Huntington's disease (HD) were determined by the use of linked DNA probes to have a high (HD+ group) or low (HD- group) probability of having inherited the mutant gene. Neuropsychological examination, performed without knowledge of DNA results, revealed impairments in five of seven subjects in the HD+ group. Abnormalities were related to visuospatial abilities or to functions associated with the frontal lobes. All three subjects in the HD- group showed no neuropsychological impairment. Statistical analyses confirmed differences between the HD+ and HD- groups. Affected parents of subjects were at least 12 years older at symptom onset. These results demonstrate that clear neuropsychological impairment may be present in HD even when overt signs and symptoms are not expected for a number of years.

Characterization of six partial deletions in the low-density-lipoprotein (LDL) receptor gene causing familial hypercholesterolemia (FH)

Two hundred thirty-four unrelated heterozygotes for familial hypercholesterolemia (FH) were screened to detect major rearrangements in the low-density-lipoprotein (LDL) receptor gene. Total genomic DNA was analyzed by Southern blot hybridization to probes encompassing exons 1-18 of the LDL receptor gene. Six different mutations were detected and characterized by the use of exon-specific probes and detailed restriction mapping. Each mutation is unique and suggests that molecular heterogeneity underlies the molecular pathology of FH. There appear to be preferential sites within the LDL receptor gene for major rearrangements resulting in deletions.

A polymorphic DNA marker that represents a conserved expressed sequence in the region of the Huntington disease gene

A polymorphic marker (D4S62) that is genetically closely linked to D4S10 and is in the region of the gene for Huntington disease is described. A four-allele polymorphism is detected when HincII-digested DNA is hybridized with D4S62. D4S62 maps, by Southern blot analysis using somatic-cell hybrids, to 4p16.1 closer to the centromere than does D4S10. The use of the polymorphisms detected by D4S62 increases the informativeness of markers close to the gene for Huntington disease and will be useful for preclinical diagnosis. D4S62 detects transcripts of approximately 6,000 nucleotides in rat, mouse, and monkey liver and brain. This represents the first demonstration of conserved expressed sequences close to the gene for Huntington disease.

The combined use of positron emission tomography and DNA polymorphisms for preclinical detection of Huntington's disease

Twenty-three persons at risk for Huntington's disease (HD) have been studied using a polymorphic human linked DNA marker (D4S10) and positron emission tomography (PET). We determined the likelihood of inheritance of the gene for HD in 13 persons, using DNA polymorphism studies. Of these, eight persons had a greater than 90% probability of being presymptomatic heterozygotes for HD. Three of these eight subjects had caudate glucose utilization detected by PET that was more than 2 standard deviations (SD) below the age-matched control mean. Measurement of caudate glucose utilization in the other five presumed presymptomatic heterozygotes revealed results between 1 and 2 SD below the mean. Five persons had a less than 10% likelihood of having inherited the abnormal gene for HD. Of these, four had normal rates of glucose utilization in the caudate nuclei. However, one individual with DNA results indicating a low risk of developing HD had abnormally low measures of caudate glucose utilization. This suggests that a recombination had occurred between the linked marker and the gene in this person. These studies suggest that PET studies of caudate glucose utilization may help to confirm results of DNA studies in some persons, and may provide an opportunity to detect when DNA results may be incorrect due to recombination.

Apolipoprotein B gene variants are involved in the determination of serum cholesterol levels: a study in normo- and hyperlipidaemic individuals

We have investigated the frequencies of 3 restriction fragment length polymorphisms (RFLPs) of the apolipoprotein B (apo B) gene in normo- and hyperlipidaemic individuals. In individuals with type III hyperlipidaemia, the allele frequency for the RFLP detected with XbaI was significantly different from the allele frequency in normolipidaemic individuals and in those with other types of hyperlipidaemia. No significant difference in allele frequency was found among these groups for the RFLPs detected with MspI or EcoRI. Within a sample of 62 normolipidaemic individuals, homozygotes for the X2 allele (cutting site) of the XbaI RFLP had a significantly higher serum cholesterol level than homozygotes for the XI allele, with individuals of the genotype X1X2 having an intermediate value (X2X2 mean 5.71 mmol/l, X1X1 mean 4.81 mmol/l, X1X2 mean 5.30 mmol/l). There were also significant differences in serum triglyceride levels in individuals with different XbaI genotypes. In these normolipidaemic individuals there was no correlation between the EcoRI and MspI RFLP genotypes and levels of any serum lipid variable. Information from the XbaI and EcoRI RFLPs was used in conjunction to define apo B haplotypes. These haplotypes are a more precise measure of the genotypic variation, and they explain a greater fraction of the serum cholesterol and triglyceride levels than the single-site polymorphisms considered separately. This study suggests that variations in the gene for apo B are associated with the determination of serum cholesterol and triglyceride levels both in patients with type III hyperlipidaemia and in the normal population.

A somatic cell hybrid panel for localizing DNA segments near the Huntington's disease gene

Thirty-four random DNA probes from the terminal half of the human chromosome 4 short arm were further localized within 4pter----p15.1. A panel of somatic cell hybrid lines defining six chromosomal regions within 4pter----p15.1 was constructed using human cell lines containing translocation or deletion chromosomes. The vast majority of the DNA sequences, 32 of 34 or 94%, mapped to the three most proximal regions comprising 4p16.1----4p15.1. Only two probes were localized distal to 4p16.1: one in the region 4p16.3----4p16.1 and one in 4p16.3. D4S10, a polymorphic DNA marker linked to the Huntington's disease defect, has previously been mapped to the terminal region of 4p with conflicting assignments to 4p16.1 and 4p16.3. Analysis of restriction fragment length polymorphisms demonstrated hemizygosity for D4S10 in a patient with Wolf-Hirschhorn syndrome resulting from an unbalanced translocation t(4;8)(p16.3;p23.1), supporting the 4p16.3 localization. Our panel of somatic cell hybrids provides a rapid method for mapping new probes to the same vicinity as that of D4S10. However, the relative paucity of such DNA segments identified here suggests that a more directed approach may be required to generate additional markers near the HD gene.

Cerebral glucose and dopa metabolism in movement disorders

The development of positron emission tomography (PET) has enabled us to perform in vivo measurements of certain aspects of regional cerebral function. Regional cerebral glucose metabolism may be readily quantified with [18F] fluoro-2-deoxyglucose (FDG) and presynaptic dopaminergic function may be studied with the labelled dopa analog 6-[18F] fluoro-L-dopa. We have applied a model to the analysis of 6-FD/PET data with which in vivo age-related changes in dopaminergic function may be demonstrated in normal subjects. With this technique, we have studied a series of asymptomatic MPTP-exposed subjects and have shown evidence of subclinical nigrostriatal pathway damage. Studies of regional cerebral glucose metabolism with FDG in early Huntington's disease have shown a characteristic impairment in caudate function which precedes the development of caudate atrophy. In addition, some asymptomatic individuals who are at risk for HD have caudate hypometabolism. We feel that, at the present time, PET provides information which is complementary to the clinical examination in establishing a diagnosis of HD. In the future these studies may also help in the investigation of at risk individuals.

Molecular genetics and Huntington's disease. The South African situation

The finding of a polymorphic DNA marker for Huntington's disease offers the potential for preclinical and prenatal screening for this condition. However, before implementation of a programme of this nature in South Africa, certain technical, medical psychosocial and ethical considerations require careful appraisal. The current situation with regard to the importance and implications of this new technology to affected kindreds is reviewed and discussed.

First-trimester prenatal diagnosis for Huntington's disease with DNA probes

Polymorphic DNA probes linked to the locus for Huntington disease (HD) were used for prenatal diagnosis of a 10-week fetus at 25% risk for the disease. The fetus proved to have a 48% risk of having inherited the HD mutation which was similar to that for the at-risk parent (50%). On this basis the parents elected to terminate the pregnancy. When appropriate family members are available and DNA studies are informative, prenatal diagnosis of HD with polymorphic DNA probes can determine the at-risk status of the fetus with 96% accuracy.

A polymorphic DNA probe located to human chromosome 4p16 (D4S62)

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DNA polymorphisms in and around the Apo-A1-CIII genes and genetic hyperlipidemias

We have studied the frequency of DNA polymorphisms in and around the apolipoprotein A-1 (Apo-A1) and apolipoprotein CIII (Apo-CIII) gene loci in 53 persons of Caucasian descent with genetic hyperlipidemias. Three restriction-fragment-length polymorphisms (RFLPs) have previously been located 5' and 3' to the Apo-A1 gene and in the Apo-CIII gene and were detected after digestion with XmnI, PstI, and SstI, respectively, and hybridization with a 2.2-kb fragment of the Apo-A1 gene. These RFLPs are in linkage equilibrium. The rare variant sites for XmnI (X2) and SstI (S2) were more frequent in familial combined hyperlipidemia (FCH) than in controls and persons with other genetic hyperlipidemias. When considered as a haplotype, this difference was significant (P less than .03). The findings in this study suggest that the previously reported association between S2 and hypertriglyceridemia may be accounted for, in part, by inclusion of numerous patients with FCH. Our data provide further evidence that these RFLPs around and within the Apo-A1/Apo-CIII genes do not participate in unmasking clinical expression in persons with familial dysbetalipoproteinemia.

Arrested epidermal morphogenesis in three newborn infants with a fatal genetic disorder (restrictive dermopathy)

Two sibs and one unrelated infant were born prematurely with taut, shiny, restrictive skin that was abnormal in structure, organization, biochemistry, and state of differentiation. Prominent abnormalities in all regions of the skin were recognized by light and electron microscopy, immunohistochemistry, and biochemistry. The epidermis was hyperplastic, hyperkeratotic, and parakeratotic. Keratohyaline granules were abnormal in structure, but the keratohyalin-derived protein filaggrin was apparently normal in quantity and biochemistry. The epidermal cells contained less than the expected quantity of high-molecular-weight, differentiation-specific keratins and the tissue stained with antikeratin antibodies in an aberrant pattern. Additional 48 and 56 kD keratin polypeptides, indicative of a hyperproliferative state, were expressed. The dermal-epidermal junction was remarkably flat and the dermis was thinner than normal. The connective tissue appeared stretched and was oriented like tendon rather than dermis. Collagen fiber bundles and fibrils were smaller in diameter than normal. The nails were normal but other epidermal appendages such as the pilosebaceous structures and the eccrine sweat glands were underdeveloped, suggesting that morphogenesis of these structures was arrested at an early stage in utero. The subcutaneous fat was at least twice the thickness of the dermis. The skin abnormalities appeared to be the cause of the flexion contractions, characteristic facies, and inability to survive because of restricted respiratory movements. The structural and biochemical abnormalities in the skin of affected infants may serve as markers for prenatal and postnatal diagnosis of the disorder, and may provide insight into the basic mechanism of the disease.

Gaucher's disease in the Cape coloured population of the RSA, including a family with 5 affected siblings

Nine Cape Coloured children from 4 families with severe non-neuropathic Gaucher's disease are documented. The diagnosis was confirmed histologically in the bone marrow, spleen and liver, and by serum acid phosphatase and leucocyte beta-glucosidase assays. This represents a minimum prevalence for Gaucher's disease of 1 in 247,350 in this population and an approximate genetic carrier rate of 1 in 230 for the abnormal gene. A family with 5 affected siblings is recorded. The severe early clinical expression documented in these coloured patients is similar to that described in the Afrikaner population and differs from the less severe expression of Gaucher's disease in the South African Ashkenazi Jewish population. Gaucher's disease in the Cape Coloured population presents with a precocious onset, causes severe complications and progresses rapidly.

Regression model for predicting dissociations of regional cerebral glucose metabolism in individuals at risk for Huntington's disease

This article describes and partially validates a method for predicting whether an observed regional metabolic value is consistent with the observed value of another region. A regression equation was generated from a set of normal metabolic values, and then this equation was applied to patients with symptomatic Huntington's disease and patients at risk for this disorder. The results of the regression method were consistent with observations of the absolute rate for the normal subjects and Huntington's patients. For the at-risk patients, 6 of 18 were found to have reduced caudate metabolism relative to observed thalamic values. Since the initial scan, one of these identified at-risk individuals has developed symptomatic Huntington's disease. The method may be appropriate for other disorders where there are potential subgroups (e.g., schizophrenia) within a diagnostic category.

Subregional assignment of the linked marker G8 (D4S10) for Huntington disease to chromosome 4p16.1-16.3

The linked DNA marker for Huntington disease has recently been mapped to the short arm of chromosome 4 by somatic cell hybridization studies. Southern blot analysis of DNA from patients with Wolf-Hirschhorn syndrome (WHS) has suggested that the linked marker maps within the terminal 4p16 band. We have now accomplished subregional assignment of G8 (D4S10) to 4p16.1-16.3 using in situ hybridization techniques on two patients with nonoverlapping interstitial deletions of 4p. The mapping of G8 (D4S10) to a region deleted in patients with WHS will allow the application of new strategies for detecting DNA sequences closer to the locus for Huntington disease.

Restrictive dermopathy: a newly recognized autosomal recessive skin dysplasia

A brother and sister from consecutive pregnancies had rigid and tightly adherent skin in association with generalized contractures, unusual facies, pulmonary hypoplasia, an abnormal placenta, and a short umbilical cord. Both died shortly after birth. Pathologic examination of the skin by light and electron microscopy showed structural abnormalities of the epidermis, dermis, and subcutaneous fat. An abnormal pattern of keratin proteins was determined biochemically using extracted epidermal proteins. Autopsy showed a normal spinal cord and muscle histology. It is postulated that the defective skin severely restricted movement and secondarily led to the other abnormalities. Familial occurrence is most consistent with autosomal recessive transmission. These patients and the primary skin defect are discussed within the framework of the Fetal Akinesia or Hypokinesia Deformation Sequence.

Positron emission tomography in the early diagnosis of Huntington's disease

We studied 10 patients with early Huntington's disease and 7 normal age-matched controls with positron emission tomography (PET) using fluorodeoxyglucose. Subjects had little or no caudate nucleus atrophy and had not received any medications. The results demonstrated that hypometabolism of glucose preceded tissue loss. Furthermore, patients with minimal neurologic or psychiatric symptoms and no obvious CT changes may be differentiated from normal persons with high accuracy by PET. PET is helpful in the early diagnosis of Huntington's disease irrespective of the mode of presentation. PET may also be useful for preclinical detection and may supplement information from DNA studies.

A family with Huntington disease and reciprocal translocation 4;5

We report the clinical and cytogenetic findings in a family in which a balanced reciprocal translocation between the long arm of chromosome 4 and the short arm of chromosome 5 is segregating together with Huntington disease in 2 generations. In situ hybridization studies revealed that the linked human DNA marker is located on the short arm of the normal and translocated chromosome 4 in the region 4p16. The association between Huntington disease and the translocation in this family may represent a chance occurrence. However, it is also possible that there is an undetected rearrangement of DNA on chromosome 4 involving the gene for Huntington disease but not affecting the site of the linked marker. Finally, the likelihood that this represents heterogeneity cannot be excluded.

Cerebral metabolism of glucose in benign hereditary chorea

Benign hereditary chorea (BHC) is an autosomal dominant disorder characterized by chorea of early onset with little or no progression. There is marked clinical variability in this disease with some subjects having onset in infancy and others with onset in early adulthood. In contrast to Huntington's disease (HD), there is no dementia. Computed tomography is normal in all subjects with no evidence of caudate nucleus atrophy. We present the results of positron emission tomography using 18F-2-fluorodeoxyglucose on three patients with this disorder from two families. Cerebral glucose metabolism in one patient was decreased in the caudate nucleus, as previously reported in HD. The other two persons from a second family showed a relative decrease in metabolic rates of glucose in the caudate when compared with the thalamus. It appears that caudate hypometabolism is not specific for HD. These findings suggest that the caudate nucleus may play a significant role in the pathophysiology of some persons with BHC.

Primary lipoprotein lipase deficiency

The enzyme lipoprotein lipase plays a central role in the processing of energy in the form of calorically dense triglyceride. Classical LPL deficiency usually presents in childhood with the multiple manifestations related to chylomicronemia. Many patients with genetic variations have been noted who differ in one of many ways from the classical patients. With the development of techniques to measure enzyme mass and to study gene expression, the molecular defects in each of these families should become evident.