Fatal infantile X-linked neuropathy.

We report a pedigree with severe X-linked neuropathy that occurs in male infants and results in death, typically by 2 years of age. The proband of our report was weak with preserved mentation. He underwent extensive evaluation, which revealed abnormal nerve conduction studies, neurogenic changes on muscle biopsy, a decreased number of large myelinated fibers and rare onion bulb formations on nerve biopsy, negative gene testing for spinal muscular atrophy, CMT1a, and CMTX1 and a normal brain magnetic resonance image. The proband's mother, an obligate carrier, had normal nerve conduction studies. Male infants with a spinal muscular atrophy phenotype but normal genetic studies should be evaluated for this fatal X-linked neuropathy.

Genetic analysis of Hispanic individuals with cystic fibrosis.

We have performed molecular genetic analyses of Hispanic individuals with cystic fibrosis (CF) in the southwestern United States. Of 129 CF chromosomes analyzed, only 46% (59/129) carry delta F508. The G542X mutation was found on 5% (7/129) of CF chromosomes. The 3849 + 10kbC-->T mutation, detected primarily in Ashkenazi Jews, was present on 2% (3/129). R1162X and R334W, mutations identified in Spain and Italy, each occurred on 1.6% (2/129) of CF chromosomes. W1282X and R553X were each detected once. G551D and N1303K were not found. Overall, screening for 22 or more mutations resulted in detection of only 58% of CF transmembrane conductance regulator gene mutations among Hispanic individuals. Analysis of KM19/XV2c haplotypes revealed an unusual distribution. Although the majority of delta F508 mutations are on chromosomes of B haplotypes, the other CF mutations are on A and C haplotypes at higher-than-expected frequencies. These genetic analyses demonstrate significant differences between Hispanic individuals with CF and those of the general North American population. Assessment of carrier/affected risk in Hispanic CF individuals cannot, therefore, be based on the mutation frequencies found through studies of the general population but must be adjusted to better reflect the genetic makeup of this ethnic group. Further studies are necessary to identify the causative mutation(s) in this population and to better delineate genotype/phenotype correlations. These will enable counselors to provide more accurate genetic counseling.

Relationship of genotype to early pulmonary function in infants with cystic fibrosis identified through neonatal screening.

To determine whether pulmonary function in infants with asymptomatic cystic fibrosis is related to genotype, we studied 18 infants with cystic fibrosis identified through neonatal screening and 18 healthy control infants. Infants with cystic fibrosis (mean age, 2.0 months; range, 1.0 to 4.6 months) were identified from June 1990 to September 1991 through a statewide screening program based on elevated immunoreactive trypsinogen concentrations. Pulmonary function testing was done before and after inhalation of albuterol. There were no differences in pulmonary function between the cystic fibrosis group and the control infants (mean age, 2.7 months; range, 0.9 to 4.5 months). However, infants homozygous for the delta F508 deletion (n = 10) differed from infants with other genotypic variants of cystic fibrosis and control infants with respect to respiratory system resistance (79.4 +/- 11.5 vs 52.0 +/- 3.8 vs 55.5 +/- 5.0 cm H2O/L per second, respectively; p = 0.04) and specific conductance (0.15 +/- 0.02 vs 0.21 +/- 0.02 vs 0.21 +/- 0.02 cm H2O-1 sec-1, respectively; p = 0.02). Infants homozygous for the delta F508 deletion, but not other infants, responded to albuterol with a decrease in respiratory system resistance. We conclude that infants with asymptomatic cystic fibrosis homozygous for the delta F508 deletion have early evidence of airways obstruction and may need early respiratory treatment.

Mutation analysis of the cystic fibrosis transmembrane regulator gene in Native American populations of the southwest.

We report DNA and clinical analyses of cystic fibrosis (CF) in two previously unstudied, genetically isolated populations: Pueblo and Navajo Native Americans. Direct mutation analysis of six mutations of the CFTR gene--namely, delta F508, G542X, G551D, R553X, N1303K, and W1282X--was performed on PCR-amplified genomic DNA extracted from blood samples. Haplotype analyses with marker/enzyme pairs XV2c/TaqI and KM19/PstI were performed as well. Of the 12 affected individuals studied, no delta F508 mutation was detected; only one G542X mutation was found. None of the other mutations was detected. All affected individuals have either an AA, AC, or CC haplotype, except for the one carrying the G542X mutation, who has the haplotype AB. Clinically, six of the affected individuals examined exhibit growth deficiency, and five (all from the Zuni Pueblo) have a severe CF phenotype. Four of the six Zunis with CF are also microcephalic, a finding not previously noted in CF patients. Our DNA data have serious implications for risk assessment of CF carrier status for these people.

Screening for cystic fibrosis: feasibility of molecular genetic analysis of dried blood specimens.

Direct genotypic analysis for the common Caucasian cystic fibrosis mutation (delta F508) was performed using dried blood specimens in a filter paper matrix (neonatal screening blotter). DNA was obtained from dried and liquid blood samples, amplified, and analyzed by polyacrylamide gel electrophoresis. Additionally, intact 4-mm-diameter punched discs from blotters containing dried blood specimen were used in the amplification reactions and analyzed by electrophoresis. The results agreed completely between these three sample types, demonstrating the feasibility of molecular genetic confirmation of the delta F508 mutation from the neonatal screening blotter among those with positive CF screening results. Such a program could reduce follow-up testing by at least 50% in a CF newborn screening program and would identify immediately those families who would benefit from carrier detection for the delta F508 allele.

Congenital adrenal hypoplasia and selective absence of pituitary luteinizing hormone: a new autosomal recessive syndrome.

Congenital hypoplasia of the adrenal glands (CHA) is a rare condition, particularly in the absence of a central nervous system (CNS) anomaly. Two major types of CHA have been described in the setting of an apparently normal CNS and pituitary: a cytomegalic type usually with X-linked recessive inheritance and a miniature adult type that, when hereditary, is an autosomal recessive trait. Glycerol kinase deficiency (GKD) is an X-linked recessive trait, and it may be associated with CHA and adrenal insufficiency, presumably because of deletion of adjacent X-linked loci. We report on three sibling infants, one male and two females, with normal CNS and lethal CHA of the miniature adult type, selective absence of pituitary LH; two of the infants also had glycerol kinase (GK) activity that was decreased but not in the GKD range. Restriction fragment length polymorphism (RFLP) analysis of X chromosome markers located at Xp21-p22 was carried out on the maternal grandfather, both parents, two of three affected infants, and a living normal brother. The results excluded the X-linked type of this disorder associated with GKD in this family. Autosomal recessive inheritance is most likely.

Subcellular distribution and kinetic properties of soluble and particulate-associated bovine adrenal glycerol kinase.

The subcellular distribution and substrate kinetics of soluble and particulate-associated bovine adrenal glycerol kinase have been investigated. Whole adrenal, adrenal cortex and adrenal medulla were examined for distribution of glycerol kinase between soluble and particulate fractions. No major differences in distribution were noted between these tissues; of the total homogenate activity, 0-20% sedimented with the nuclear fraction, 24-36% sedimented with the post-nuclear fraction and 64-69% remained soluble. Steady-state kinetic parameters of glycerol kinase activity were compared in the soluble and mitochondrial fractions. The Km for glycerol in the soluble fraction was 6.3 +/- 0.1 microM and in the mitochondrial fraction was 4.0 +/- 0.3 microM. The Km for ATP in soluble fraction was 12.8 +/- 1.5 and in the mitochondrial fraction was 5.3 +/- 1.6. Release of adrenal glycerol kinase from the mitochondrial fraction was investigated using inorganic phosphate, ATP and glycerol 3-phosphate. Of these compounds, only ATP and glycerol 3-phosphate were effective in releasing particulate-associated glycerol kinase. Inorganic phosphate had no effect upon release. Particulate-associated glycerol kinase activity of the mitochondrial fraction was stimulated by addition of succinate and ADP and was inhibited by addition of atractyloside. The data presented here indicate that bound glycerol kinase found within the mitochondrial fraction is kinetically distinct from soluble glycerol kinase and binding to mitochondria is responsive to substrate and product levels within the physiological range.

Human and rat adrenal glycerol kinase: subcellular distribution and bisubstrate kinetics.

The subcellular distribution of adrenal glycerol kinase in man and rat are reported and the bisubstrate kinetics of the soluble enzyme are compared in these two species. The specific activity of glycerol kinase in human whole adrenal homogenate (145 microU/mg protein) was 3 times that found in rat whole adrenal homogenate (48 microU/mg protein). In both species 8% of the total glycerol kinase activity was associated with the nuclear pellet fraction. In human, 62% of the total activity was soluble, while 24% was associated with the postnuclear particulate fraction. Rat glycerol kinase activity was also predominantly soluble: 69% of the total activity was soluble and 13% was in the postnuclear particulate fraction. The apparent Km for glycerol in soluble adrenal glycerol kinase was similar in both species, 2.8 microM in human and 3.1 microM in rat. The apparent Km for ATP in soluble human adrenal glycerol kinase was 22.0 microM. In rat the enzyme did not appear to follow Michaelis-Menten kinetics with ATP as substrate. The Vmax for the soluble enzyme was similar in both human and rat. This report provides a background to biochemical investigations on human glycerol kinase deficiency, an inborn error of metabolism which may be characterized by adrenal hypoplasia and insufficiency.

Human glycerol kinase deficiency: enzyme kinetics and fibroblast hybridization.

Glycerol kinase deficiency has been associated with neuromuscular, skeletal and adrenal abnormalities and has also been seen in individuals without these clinical findings. Examination of residual enzyme activity in patients' liver, kidney, leukocytes and fibroblasts showed a generalized, heritable defect: the apparent Km for glycerol was increased 5-200-fold over control values, whereas the apparent Km for ATP was not significantly altered. This kinetic defect was similar in fibroblasts from clinically different individuals with this inborn error of metabolism. Hybridization of fibroblasts from these individuals showed no evidence of complementation for glycerol kinase activity.