Arginine to ornithine ratio as a diagnostic marker in patients with positive newborn screening for hyperargininemia

Arginase deficiency is a rare inborn error of metabolism that interrupts the final step of the urea cycle. Untreated individuals often present with episodic hyperammonemia, developmental delay, cognitive impairment, and spasticity in early childhood. The newborn screening (NBS) algorithms for arginase deficiency vary between individual states in the US but often include hyperargininemia and elevated arginine to ornithine (Arg/Orn) ratio. Here, we report 14 arginase deficiency cases, including two patients with positive NBS for hyperargininemia in whom the diagnosis of arginase deficiency was delayed owing to normal or near normal plasma arginine levels on follow-up testing. To improve the detection capability for arginase deficiency, we evaluated plasma Arg/Orn ratio as a secondary diagnostic marker in positive NBS cases for hyperargininemia. We found that plasma Arg/Orn ratio combined with plasma arginine was a better marker than plasma arginine alone to differentiate patients with arginase deficiency from unaffected newborns. In fact, elevated plasma arginine in combination with an Arg/Orn ratio of ≥1.4 identified all 14 arginase deficiency cases. In addition, we examined the impact of age on plasma arginine and ornithine levels. Plasma arginine increased 0.94 μmol/L/day while ornithine was essentially unchanged in the first 31 days of life, which resulted in a similar increasing trend for the Arg/Orn ratio (0.01/day). This study demonstrated that plasma Arg/Orn ratio as a secondary diagnostic marker improved the detection capability for arginase deficiency in newborns with hyperargininemia, which will allow timely detection of arginase deficiency and hence initiation of treatment before developing symptoms.

Further Delineation of Ribose-5-phosphate Isomerase Deficiency: Report of a Third Case

Ribose-5-phosphate isomerase deficiency, a disorder of the pentose phosphate shunt, was described in 1999. There are 2 previously reported cases of ribose-5-phosphate isomerase deficiency. Here, we describe the clinical course, diagnostic odyssey, and molecular findings in the third case of ribose-5-phosphate isomerase deficiency to further delineate the syndrome. Whole-exome sequencing demonstrated 2 mutations in the ribose-5-phosphate isomerase gene, RPIA, in a child with neonatal onset leukoencephalopathy and psychomotor delays. Urine polyols were elevated confirming deficiency of ribose-5-phosphate isomerase (RPI, EC. 5.3.1.6) and pathogenicity of the variants. Measurement of urine polyols should be considered in cases of early-onset white-matter disease.

Congenital Glucose-Galactose Malabsorption: A Case Report

Congenital glucose-galactose malabsorption (CGGM) is a rare cause of intractable infantile diarrhea, with only a few hundred cases recognized worldwide. This life-threatening disorder must be considered in the differential diagnosis of an infant who presents with diarrhea and dehydration that fails to respond to standard therapy. The clinical and diagnostic course of an infant with recurrent episodes of watery diarrhea and hypernatremic dehydration found to be homozygous for a rare variant in the SLC5A1 gene, c.187C>T (p.R63X) is described.

HUWE1 mutations in Juberg-Marsidi and Brooks syndromes: the results of an X-chromosome exome sequencing study

BACKGROUND

X linked intellectual disability (XLID) syndromes account for a substantial number of males with ID. Much progress has been made in identifying the genetic cause in many of the syndromes described 20-40 years ago. Next generation sequencing (NGS) has contributed to the rapid discovery of XLID genes and identifying novel mutations in known XLID genes for many of these syndromes.

METHODS

2 NGS approaches were employed to identify mutations in X linked genes in families with XLID disorders. 1 involved exome sequencing of genes on the X chromosome using the Agilent SureSelect Human X Chromosome Kit. The second approach was to conduct targeted NGS sequencing of 90 known XLID genes.

RESULTS

We identified the same mutation, a c.12928 G>C transversion in the HUWE1 gene, which gives rise to a p.G4310R missense mutation in 2 XLID disorders: Juberg-Marsidi syndrome (JMS) and Brooks syndrome. Although the original families with these disorders were considered separate entities, they indeed overlap clinically. A third family was also found to have a novel HUWE1 mutation.

CONCLUSIONS

As we identified a HUWE1 mutation in an affected male from the original family reported by Juberg and Marsidi, it is evident the syndrome does not result from a mutation in ATRX as reported in the literature. Additionally, our data indicate that JMS and Brooks syndromes are allelic having the same HUWE1 mutation.

Congenital mirror movements: mutational analysis of RAD51 and DCC in 26 cases

OBJECTIVE

We screened a large series of individuals with congenital mirror movements (CMM) for mutations in the 2 identified causative genes, DCC and RAD51.

METHODS

We studied 6 familial and 20 simplex CMM cases. Each patient had a standardized neurologic assessment. Analysis of DCC and RAD51 coding regions included Sanger sequencing and a quantitative method allowing detection of micro rearrangements. We then compared the frequency of rare variants predicted to be pathogenic by either the PolyPhen-2 or the SIFT algorithm in our population and in the 4,300 controls of European origin on the Exome Variant Server.

RESULTS

We found 3 novel truncating mutations of DCC that segregate with CMM in 4 of the 6 families. Among the 20 simplex cases, we found one exonic deletion of DCC, one DCC mutation leading to a frameshift, 5 missense variants in DCC, and 2 missense variants in RAD51. All 7 missense variants were predicted to be pathogenic by one or both algorithms. Statistical analysis showed that the frequency of variants predicted to be deleterious was significantly different between patients and controls (p < 0.001 for both RAD51 and DCC).

CONCLUSION

Mutations and variants in DCC and RAD51 are strongly associated with CMM, but additional genes causing CMM remain to be discovered.

When the usual symptoms become an unusual diagnosis: a case report of trifunctional protein complex

Disorders of mitochondrial fatty acid b-oxidation should be considered in any infant who presents with unexplained hypoglycemia and/or myopathy. Although disorders of trifunctional protein (TFP) complex including long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) and mitochondrial TFP deficiencies are extremely rare, the combined incidence of mitochondrial fatty acid disorders is quite frequent. With the expansion of newborn screening, what were once considered uncommon disorders are being identified with increasing frequency in asymptomatic infants. The following case scenario presents an infant who developed symptoms prior to the completion of newborn screening. This fairly routine course for a late-preterm infant reveals an extremely rare inborn error of metabolism, LCHAD deficiency. An overview of TFP complex, the differential diagnoses as the case unfolds, diagnostic test results, acute care management, and short-term patient follow-up is presented. With experience, health care providers often become accustomed to and expect to see common things regularly. This case presents a scenario which, as it unfolds, appears to be quite common. It turns out, however, to be very uncommon.

Combining fetal sonography with genetic and allele pathogenicity studies to secure a neonatal diagnosis of Bardet-Biedl syndrome

Bardet-Biedl syndrome (BBS) is a rare pediatric ciliopathy characterized by marked clinical variability and extensive genetic heterogeneity. Typical diagnosis of BBS is secured at a median of 9 years of age, and sometimes well into adolescence. Here, we report a patient in whom prenatal detection of increased nuchal fold, enlarged echogenic kidneys, and polydactyly prompted us to screen the most commonly mutated genes in BBS and the phenotypically and genetically overlapping ciliopathy, Meckel-Gruber syndrome (MKS). We identified the common Met390Arg mutation in BBS1 in compound heterozygosity with a novel intronic variant of unknown significance (VUS). Testing of mRNA harvested from primary foreskin fibroblasts obtained shortly after birth revealed the VUS to induce a cryptic splice site, which in turn led to a premature termination and mRNA degradation. To our knowledge, this is the earliest diagnosis of BBS in the absence of other affected individuals in the family, and exemplifies how combining clinical assessment with genetic and timely assays of variant pathogenicity can inform clinical diagnosis and assist with patient management in the prenatal and neonatal setting.

Partial trisomy 10p12.33 and partial monosomy 13q32.1: case report and a literature review

We report on a preterm neonate with a deletion of the distal long arm of chromosome 13q32.1 and partial trisomy of the short arm of chromosome 10p12.33. The patient has intrauterine growth retardation, microphthalmia, macrocephaly, holoprosencephaly, patent ductus arteriosus, aortic isthmus hypoplasia, right renal agenesis, imperforate anus, ambiguous genitalia, pleural effusion and vertebral anomaly. Analysis using an oligonucleotide microarray (U-array Cyto6000 array platform (Human Genome build: hg 18) indicated that there was a partial trisomy of chromosome 10(19.5 Mb gain) involving 298 oligonucleotides from 10pter to 10p12.33, and a partial monosomy of chromosome 13(18.3 Mb deleted) involving 313 oligonucleotides from 13q32.1 to 13qter. This is the first report of a patient with partial trisomy 10p12.33 and partial monosomy 13q32.1.

New RAB3GAP1 mutations in patients with Warburg Micro Syndrome from different ethnic backgrounds and a possible founder effect in the Danish

Warburg Micro Syndrome is a rare, autosomal recessive syndrome characterized by microcephaly, microphthalmia, microcornia, congenital cataracts, optic atrophy, cortical dysplasia, in particular corpus callosum hypoplasia, severe mental retardation, spastic diplegia, and hypogonadism. We have found five new mutations in the RAB3GAP1 gene in seven patients with suspected Micro Syndrome from families with Turkish, Palestinian, Danish, and Guatemalan backgrounds. A thorough clinical investigation of the patients has allowed the delineation of symptoms that are consistently present in the patients and may aid the differential diagnosis of Micro Syndrome for patients in the future. All patients had postnatal microcephaly, micropthalmia, microcornia, bilateral congenital cataracts, short palpebral fissures, optic atrophy, severe mental retardation, and congenital hypotonia with subsequent spasticity. Only one patient had microcephaly at birth, highlighting the fact that congenital microcephaly is not a consistent feature of Micro syndrome. Analysis of the brain magnetic resonance imagings (MRIs) revealed a consistent pattern of polymicrogyria in the frontal and parietal lobes, wide sylvian fissures, a thin hypoplastic corpus callosum, and increased subdural spaces. All patients were homozygous for the mutations detected and all mutations were predicted to result in a truncated RAB3GAP1 protein. The analysis of nine polymorphic markers flanking the RAB3GAP1 gene showed that the mutation c.1410C>A (p.Tyr470X), for which a Danish patient was homozygous, occurred on a haplotype that is shared by the unrelated heterozygous parents of the patient. This suggests a possible founder effect for this mutation in the Danish population.

Exclusion of APC and VHL gene deletions by array-based comparative hybridization in two patients with microscopically visible chromosomal aberrations

Karyotyping is a major component of the genetic work-up of patients with dysmorphism. Cytogenetic aberrations close to a known tumor suppressor gene raise important clinical issues because deletion of that tumor suppressor gene can cause genetic predisposition to cancer. We present two cancer-free dysmorphic patients with karyotypes of 46,XX,del(5)(q15q22.3) and 46,XX,del(3)(p25.2~pter). These deletions are close to the APC and VHL genes that confer susceptibility to familial Adenomatous polyposis (OMIM #17510) and von-Hippel-Lindau syndrome (OMIM #193300), respectively. The array-based comparative genomic hybridization (array-CGH) analysis using a custom Agilent 44K oligonucleotide array demonstrated an interstitial 20.7-megabase (Mb) deletion on 5q (chr5: 89,725,638-110,491,345) and a terminal 9.45-Mb deletion on 3p (chr3:pter-9,450,984). According to the March 2006 human reference sequence, the APC gene is located at chr5: 112,101,483-112,209,835 and the VHL gene is located at chr3: 10,158,319-10,168,746. These results indicate that the APC gene is 2,300 kilobases (kb) and the VHL gene is 700 kb away from deleted regions. Southern blot analysis for APC and VHL genes were negative, consistent with array-CGH findings. These results demonstrate the power of array-CCH to assess potential tumor suppressor gene involvement and cancer risk in patients with microscopically visible deletions in areas near tumor suppressors.

Further delineation of interstitial chromosome 6 deletion syndrome and review of the literature

Interstitial deletions of chromosome 6q are a relatively rare finding. Deletions have ranged from the loss of a single band to larger deletions spanning multiple bands. The clinical phenotype varies, but some features commonly seen include cardiac anomalies, hypotonia, facial dysmorphism and mental retardation. To further delineate the syndrome, we report an infant with facial dysmorphism, ectrodactyly and tetralogy of Fallot owing to interstitial deletion 6q16.1-6q22.32. On array comparative genomic hybridization analysis, the deletion spanned from the 93 377 323rd base to the 127 650 582nd base on chromosome 6 [coordinates are based on Human Mar. 2006 (hg18) assembly of International Human Genome Sequencing Consortium]. A literature review identified 16 additional cases with overlapping interstitial deletions of chromosome 6q between q13 and q23.1. Genotype-phenotype correlations are considered.

Telomere shortening in T lymphocytes of older individuals with Down syndrome and dementia

Telomere shortening has been recently correlated with Alzheimer's disease status. Therefore, we hypothesized that a possible association might exist for adults with Down syndrome (DS). Using blind, quantitative telomere protein nucleic acid FISH analyses of metaphase and interphase preparations from 18 age-matched trisomy 21 female study participants with and without dementia, we have observed increased telomere shortening in adults with DS and dementia (p < .01). From this initial study, we conclude that telomere shortening is associated with dementia in this high-risk population and suggest that additional research may show that telomere shortening may be a biological marker of dementia status.

Neonatal Gaucher disease presenting as persistent thrombocytopenia

Mutations in the beta-glucocerebrosidase gene cause Gaucher disease with the type 1 variant generally presenting later in life with mild disease and type 2 in infancy with severe neuronopathic symptoms. We describe a neonate homozygous for the D409 H mutation with thrombocytopenia, splenomegaly and cholestasis at birth as the major features.

Prenatal diagnostic testing for infantile and late-infantile neuronal ceroid lipofusinoses (NCL) using allele specific primer extension (ASPE)

Infantile (INCL, NCL1) and late-infantile (LINCL, NCL2) neuronal ceroid lipofuscinoses have been found to result from genetic deficiency of genes CLN(1 ) and CLN(2), respectively. The application of molecular analyses can facilitate prenatal diagnosis for families affected by NCL1 or NCL2, in which the familial mutation(s) have been identified. Molecular testing with allele-specific primer extension and DNA sequencing was performed in nine pregnancies, four from two NCL1 families and five from five NCL2 families. Lysosomal enzyme activity assays were carried out as well.Four fetuses from three pregnancies in NCL1 families were found to be carriers for a mutation 451C-T in the CLN(1) gene and one was normal. Prenatal testing of three NCL2 families who carried mutation R208X in the CLN(2) gene showed that all fetuses were carriers. In NCL2 families who carried either mutation IVS5-1C or/and IVS5-1A two normal pregnancies were detected. Our studies indicate that DNA testing, which may provide definitive prenatal diagnosis for NCL, may be used in combination with lysosomal enzyme activity analyses.

Proteomic studies identified a single nucleotide polymorphism in glyoxalase I as autism susceptibility factor

Autism is a neurodevelopmental disability characterized by deficits in verbal communications, impairments in social interactions, and repetitive behaviors. Several studies have indicated strong involvement of multigenic components in the etiology of autism. Linkage analyses and candidate gene search approaches so far have not identified any reliable susceptibility genes. We are using a proteomic approach to identify protein abnormalities due to aberrant gene expression in autopsied autism brains. In four of eight autism brains, we have found an increase in polarity (more acidic) of glyoxalase I (Glo1) by two-dimensional gel electrophoresis. To identify the molecular change resulting in the shift of Glo1 polarity, we undertook sequencing of GLO1 gene. Direct sequencing of GLO1 gene/mRNA in these brains, has identified a single nucleotide polymorphism (SNP), C419A. The SNP causes an Ala111Glu change in the protein sequence. Population genetics of GLO1 C419A SNP studied in autism (71 samples) and normal and neurological controls (49 samples) showed significantly higher frequency for the A419 (allele frequency 0.6 in autism and 0.4 in controls, one-tailed Fisher's test P < 0.0079). Biochemical measurements have revealed a 38% decrease in Glo1 enzyme activity in autism brains (one-tailed t-test P < 0.026). Western blot analysis has also shown accumulation of advanced glycation end products (AGE's) in autism brains. These data suggest that homozygosity for A419 GLO1 resulting in Glu111 is a predisposing factor in the etiology of autism.

UV light synergistically enhances the cardiotoxic effects of interleukin 1beta through peroxynitrite formation

BACKGROUND

Proinflammatory cytokines play an important role in chronic cardiac diseases.

METHODS AND RESULTS

Neonatal rat cardiomyocytes were exposed to interleukin (IL)-1beta (2 ng/mL) for 4 days. We assessed contractility through videomicroscopy and calcium transients with the Ca(2+)-sensitive dye fura-2. In IL-1beta-treated cells, the UV excitation (380 nm) necessary to induce dye fluorescence effected a rapid cessation of Ca(2+) transients and contraction, accompanied by calcium overload originating from an intracellular compartment. This occurred in the absence of fura-2 but required UV illumination. Incubation with 10 mmol/L N-acetylcysteine prevented this response, suggesting a free radical-mediated event. However, exposure to IL-1beta either increased or did not change the activity of the free radical scavengers superoxide dismutase, catalase, and glutathione peroxidase. In contrast, lipid peroxidation increased by 600% (P < or =.0001) in the IL-1beta plus UV-treated cells, an effect eliminated by L-NMMA. L-NMMA also completely abolished the UV-mediated cytotoxicity. We used immunohistochemistry to localize nitrotyrosine accumulation in the myocytes cotreated with IL-1beta and UV, an effect that was also blocked by L-NMMA.

CONCLUSIONS

We hypothesize that the toxic radical peroxynitrite, arising from nitric oxide and superoxide anion, may be responsible for tetany and acute cardiomyocyte death. These results demonstrate the potential role of peroxynitrite in cardiotoxicity, which may be important in cardiac diseases associated with proinflammatory cytokines.

Lysosomal ceroid depletion by drugs: therapeutic implications for a hereditary neurodegenerative disease of childhood

Neuronal ceroid lipofuscinoses (NCLs) are the most common hereditary neurodegenerative diseases of childhood. The infantile form, INCL, is caused by lysosomal palmitoyl-protein thioesterase (PPT) deficiency, which impairs the cleavage of thioester linkages in palmitoylated proteins, preventing their hydrolysis by lysosomal proteinases. Consequent accumulation of these lipid-modified proteins (constituents of ceroid) in lysosomes leads to INCL. Because thioester linkages are susceptible to nucleophilic attack, drugs with this property may have therapeutic potential for INCL. We report here that two such drugs, phosphocysteamine and N-acetylcysteine, disrupt thioester linkages in a model thioester compound, [14C]palmitoyl approximately CoA. Most importantly, in lymphoblasts derived from INCL patients, phosphocysteamine, a known lysosomotrophic drug, mediates the depletion of lysosomal ceroids, prevents their re-accumulation and inhibits apoptosis. Our results define a novel pharmacological approach to lysosomal ceroid depletion and raise the possibility that nucleophilic drugs such as phosphocysteamine hold therapeutic potential for INCL.

Specific substrate for CLN2 protease/tripeptidyl-peptidase I assay

The classic late infantile neuronal ceroid lipofuscinosis (LINCL, CLN2) is a fatal neurodegenerative disorder that results from mutations in a gene encoding a lysosomal proteinase, known as CLN2 protease (CLN2p) or tripeptidyl peptidase I (TPP-I). Three different substrates, fluorescein isothiocyanate-labelled haemoglobin, A-F-F-7-amino-4-methylcoumarin (AAF-AMC) and G-F-F-L-7-amino-4-trifluoromethylcoumarin (GFFL-AFC) have been used for the CLN2p/TPP-I assay with varying degrees of residual activities in patients with LINCL. Further, conclusive identification of carriers are not possible with the first two substrates. An assay for the CLN2p/TPP-I based on the cleavage of amino terminal tripeptide from G-F-F-L-AFC was applied to prenatal and postnatal diagnosis of LINCL patients and heterozygote carriers. In leukocytes, the CLN2p/TPP-I activities in controls and heterozygote carriers were 1995 +/- 154 (n = 15) and 918 +/- 253 (n = 15) nmol/h/mg protein respectively. No CLN2p/TPP-I activity was detectable in all but two patients. These two patients had less than 2% residual activity, and had delayed clinical symptoms for LINCL. This shows that the G-F-F-L-AFC is a highly specific substrate for the CLN2p/TPP-I assay. The fact that with this substrate the enzyme cleaves a peptide bond between the two amino acids may be the reason for the high level of specificity.

Atypical late infantile and juvenile forms of neuronal ceroid lipofuscinosis and their diagnostic difficulties

We have collected 122 late-infantile neuronal ceroid lipofuscinosis (LINCL, CLN2) and 191 juvenile NCL (JNCL, CLN3) cases, diagnosed on the basis of age-at-onset, clinical symptomatology, and pathological findings and representing the most common forms of NCL in the United States, and Europe. However, careful analysis of available data revealed that about 80% of cases show typical and 20% show atypical clinical course and/or pathological findings and thus, may represent variants of LINCL and JNCL, respectively. Recent progress in the biochemistry and molecular genetics of NCL inclined us to reevaluate these atypical NCL cases. The gene responsible for LINCL has not yet been identified, except for the Finnish variant. Accumulation of subunit c of mitochondrial ATP synthase, to curvilinear profiles, is found in LINCL cases. A novel variant of LINCL, with predominantly granular profiles in the lysosomal storage, as well as normal excretion of subunit c in urine samples, was found in five cases. When the palmitoyle-protein thioesterase (PPT) was studied in these five cases, it was found that the level was deficient, suggesting that they are not LINCL, but the infantile form of neuronal ceroid lipofuscinosis (INCL). Using molecular genetic techniques in the typical JNCL cases, common 1.02 kb deletion to CLN3 was found in 23/27 (homozygotes) and in one allele 4/27 (heterozygotes) in affected pedigrees. In atypical JNCL pedigrees, it was found in 5/16 heterozygotes, while in 1/5 pedigrees, a novel mutation of one atypical JNCL where a single amino acid substitution at 295 E-->K was found in one allele. None of the atypical JNCL cases was homozygote. In atypical JNCL cases where mutation in CLN3 has not been identified (11/16 probands), several possibilities may exist. The phenotype may be caused by a yet undefined mutation in CLN3 or may be due to phenotypically overlapping with other forms of NCL. Pheno/genotypic correlation and the diagnostic difficulties are discussed.

Fragile X syndrome in two siblings with major congenital malformations

We report on 2 brothers with both fragile X and VACTERL-H syndrome. The first sibling, age 5, had bilateral cleft lip and palate, ventricular septal defect, and a hypoplastic thumb. The second sibling, age 2 1/2, had a trachesophageal fistula, esophageal atresia, and vertebral abnormality. High-resolution chromosome analysis showed a 46, XY chromosome constitution in both siblings. By PCR and Southern blot analysis, the siblings were found to have large triplet repeat expansions in the fragile X gene (FMR 1) and both had methylation mosaicism. Enzyme kinetic studies of iduronate sulfatase demonstrated a two-fold increase in activity in the first sib as compared to the second. Possible mechanisms through which the fragile X mutation can cause down-regulation of adjacent loci are discussed.

A common mutation site in the beta-galactosidase gene originates in Puerto Rico

Several mutation sites have been found in the beta-galactosidase gene of patients with GM1 gangliosidosis. In a previous report we found a common point mutation site in American patients with GM1 gangliosidosis resulting in a 208Arg --> Cys amino acid substitution. From the patients' family history, we suggested that this mutation may have come to South and North America via Puerto Rico. Four new patients with infantile GM1 gangliosidosis have been analyzed with allele-specific hybridization. Two siblings from Puerto Rico of Spanish ancestry are homozygous for this mutation. Another patient also from Puerto Rico is heterozygous for this allele, and another black patient does not have this mutation. These results support our initial hypothesis that this mutation has probably arisen in Puerto Rico.

Abnormal acid phosphatases in neuronal ceroid-lipofuscinoses

Acid phosphatases in brain and cultured lymphoblasts from patients affected with neuronal ceroid-lipofuscinoses (NCL) were studied by starch gel electrophoresis. After electrophoresis the gel was incubated with 4-methyl umbelliferyl phosphate at pH 4.5 and the fluorescent reaction product was visualized under ultraviolet light. Control brain showed a single band with mobility of about 1 cm while NCL patients showed two additional fast moving bands. In the late-infantile, and in the adult form (Kufs disease), the middle band was prominent while the fast moving band was predominant in juvenile NCL. In long-term lymphoblasts, controls showed a single band of acid phosphatase activity while both juvenile and late-infantile NCL showed two additional fast moving bands. Obligate heterozygotes showed reduced levels of the fast moving bands. Fluorometric assay of acid phosphatase using 4-methylumbelliferyl phosphate as substrate showed a 2-fold increase in activity in the patients. The increased acid phosphatase activity is completely inhibited by tartrate. Lymphocyte hexosamnidase activities were unchanged in NCL patients lymphoblasts. Studies on brains of NCL patients and on cultured lymphoblasts from families with late-infantile and juvenile form of NCL showed that abnormal acid phosphatase is characteristic of NCL.

Molecular carrier testing for the fragile X syndrome: Issues for genetic counselors

Molecular analysis of the fragile X (FMR-1) gene identifies female fragile X carriers, but appropriate genetic counseling can only be provided if the limitations of the testing methods are understood. Molecular analysis of this gene is achieved with both the polymerase chain reaction (PCR) and Southern blot techniques. PCR is faster and can determine the actual number of CGG repeats, which modifies genetic counseling substantially. However, for a sizeable percentage of women, PCR alone is not conclusive, and Southern analysis is necessary to complete the study. While this procedure takes longer, it is usually conclusive. Women who present for genetic counseling and carrier testing in the second trimester of pregnancy need this information quickly, and for them the turn-around time is paramount. It is critical that genetic counselors understand these methods so that they can educate their clients and facilitate appropriate follow-up.

New X-linked mental retardation (XLMR) syndrome with distinct facial appearance and growth retardation

We report on 2 brothers and their nephew with an apparently new X-linked mental retardation (XLMR) syndrome characterized by a distinct facial appearance, growth retardation, and severe mental retardation. The facial traits included triangular shape; bifrontal narrowness; malar flatness; blepharophimosis; very deeply set eyes; epicanthus inversus; bulbous nose; low hairline; low-set, deeply cupped, and protruding ears; short ill-defined philtrum; and thin tented upper lip. These facial anomalies are particularly striking and recognizable even at birth. The boys were small for gestational age and remained below -2 SD in growth parameters. With age, large joint contractures developed. Pectus excavatum was apparent at birth but became more obvious with age. Global developmental delay was evident in infancy. The brothers were nonverbal while their nephew spoke simple words. Optic atrophy, esotropia, nystagmus, and spastic diplegia were evident. They were self-abusive, hyperactive, and poorly coordinated. CT scans demonstrated atrophic hydrocephalus. No EEG abnormalities were detected. Karyotypes were 46,XY and fragile X negative. Routine chemistries; amino, organic, and uronic acids; oligosaccharides; lysosomal enzymes; and very long chain fatty acids were normal. Remarkable phenotypic similarity between these brothers and their nephew and lack of manifestations in their mothers makes X-linked recessive inheritance likely. This syndrome, which does not appear to have been reported previously, adds to the delineation of XLMR.

A de novo 13 nt deletion, a newly identified C647W missense mutation and a deletion of exon 18 in infantile onset glycogen storage disease type II (GSDII)

We identified the presumably rare event of de novo mutation in an autosomal recessive disorder, glycogen storage disease type II (GSDII). GSDII results from inherited deficiency of acid alpha-glucosidase (acid maltase) and both the expressed and structural gene (designated GAA) have been isolated. The mutation was a deletion of 13 nt of coding sequence (delta nt 1456-1468) on the paternally derived allele of the proband. The delta nt 1456-1468 results in a reading frameshift and a premature termination signal upstream of the enzyme catalytic site. Paternity was confirmed by presence of two downstream, uncommon amino acid substitutions (E689K, W746C) in both proband and father and by comparison of nine short tandem repeats. The maternal allele carried a newly identified deleterious C647W missense mutation in a highly conserved area of the protein. The C647W mutation was also found in a second unrelated proband, heteroallelic with a deletion extending from IVS17 to IVS18.

Rapid fragile X carrier screening and prenatal diagnosis using a nonradioactive PCR test

OBJECTIVE

To develop a rapid, nonradioactive test using the polymerase chain reaction (PCR) capable of detecting full fragile X mutations, premutations, and resolving normal alleles and to apply this to prenatal diagnosis and carrier screening of pregnant women at risk for fragile X carrier status.

DESIGN

Prenatal and blood sample PCR analysis with confirmation by direct Southern blotting and cytogenetic techniques.

SETTING

Samples sent to a DNA diagnostic research laboratory at a tertiary referral center.

PARTICIPANTS

Pregnant women with a family history of undiagnosed mental retardation or known fragile X syndrome and controls.

RESULTS

A rapid, nonradioactive PCR screening protocol for the fragile X mental retardation-1 gene for both normal and mutant alleles was developed. Analysis of 570 control X chromosomes showed a modal number of 30 CGG repeats (range, 12 to 52 repeats) and a calculated heterozygosity of approximately 80%. No excess of homozygosity was found, indicating the test was accurate for normal allele resolution. In addition, 150 unrelated pregnant women were screened. Within known fragile X families, five of 20 pregnant women were diagnosed as carriers. Two new fragile X families were diagnosed among relatives of 130 females with family histories of undiagnosed mental retardation, although no carriers were identified. Prenatal PCR testing of 28 carriers accurately detected nine fetuses with full mutations.

CONCLUSIONS

This rapid, nonradioactive PCR protocol allows accurate resolution of normal alleles as well as simultaneous detection of carrier alleles and full mutations. With this approach, efficient screening of pregnant women at risk for fragile X carrier status, subsequent genetic counseling of identified carriers, and reliable prenatal diagnosis can be offered.

Metabolic studies in a mouse model of hepatorenal tyrosinemia: absence of perinatal abnormalities

Radiation induced chromosomal deletions at the albino locus in the mouse, lethal when homozygous, cause abnormalities of expression of several unlinked liver specific genes. Recently, the gene encoding FAH was shown to be included in the deletions. Since in humans FAH mutations cause tyrosinemia type I, deletion homozygous mice were suspected of having tyrosinemia. Studies of plasma amino acids did not confirm this suspicion. Also, succinylacetone levels were normal in fetal and newborn livers of deletion homozygotes. The present evidence, therefore, does not support the assumption that the earlier described ultrastructural and enzyme abnormalities in deletion homozygotes are secondary effects of tyrosinemia caused by the deletion of FAH.