Patricia Galvin-Parton

Newborn screening for Krabbe disease: the New York State model.

Krabbe disease is a rare inherited neurologic disorder affecting the central and peripheral nervous systems. The disease has four phenotypes: early infantile, later onset, adolescent, and adult. The only known treatment is hematopoietic stem cell transplantation, which is, in the early infantile form of the disease, most beneficial if performed before onset of clinical symptoms. In August 2006, New York State began screening all newborns for Krabbe disease. A rapid and accurate technique for assessing galactocerebrosidase activity and performing DNA mutation analysis had been developed. Interpreting these results was limited, however, because neither enzyme activity nor genetic mutation reliably predicts phenotype. A series of initiatives were therefore developed by a multidisciplinary group of neurologists, geneticists, metabolic pediatricians, neurodevelopmental pediatricians, and transplant physicians (the Krabbe Consortium of New York State) to enhance the effectiveness of the newborn screening program. A standardized clinical evaluation protocol was designed based on the available literature, criteria for transplantation for the early infantile phenotype were formulated, a clinical database and registry was developed, and a study of developmental and functional outcomes was instituted. This multidisciplinary standardized approach to evaluating infants who have positive results on newborn screening may serve as a model for other states as they begin the process of screening for Krabbe disease and other lysosomal storage disorders.

Mutation Analysis and Embryonic Expression of the HLXB9 Currarino Syndrome Gene

The HLXB9 homeobox gene was recently identified as a locus for autosomal dominant Currarino syndrome, also known as hereditary sacral agenesis (HSA). This gene specifies a 403-amino acid protein containing a homeodomain preceded by a very highly conserved 82-amino acid domain of unknown function; the remainder of the protein is not well conserved. Here we report an extensive mutation survey that has identified mutations in the HLXB9 gene in 20 of 21 patients tested with familial Currarino syndrome. Mutations were also detected in two of seven sporadic Currarino syndrome patients; the remainder could be explained by undetected mosaicism for an HLXB9 mutation or by genetic heterogeneity in the sporadic patients. Of the mutations identified in the 22 index patients, 19 were intragenic and included 11 mutations that could lead to the introduction of a premature termination codon. The other eight mutations were missense mutations that were significantly clustered in the homeodomain, resulting, in each patient, in nonconservative substitution of a highly conserved amino acid. All of the intragenic mutations were associated with comparable phenotypes. The only genotype-phenotype correlation appeared to be the occurrence of developmental delay in the case of three patients with microdeletions. HLXB9 expression was analyzed during early human development in a period spanning Carnegie stages 12-21. Signal was detected in the basal plate of the spinal cord and hindbrain and in the pharynx, esophagus, stomach, and pancreas. Significant spatial and temporal expression differences were evident when compared with expression of the mouse Hlxb9 gene, which may partly explain the significant human-mouse differences in mutant phenotype.

Ethnically diverse causes of Walker-Warburg syndrome (WWS): FCMD mutations are a more common cause of WWS outside of the Middle East.

Walker‐Warburg syndrome (WWS) is a genetically heterogeneous autosomal recessive disease characterized by congenital muscular dystrophy, cobblestone lissencephaly, and ocular malformations. Mutations in six genes involved in the glycosylation of á‐dystroglycan (POMT1, POMT2, POMGNT1, FCMD, FKRP and LARGE) have been identified in WWS patients, but account for only a portion of WWS cases. To better understand the genetics of WWS and establish the frequency and distribution of mutations across WWS genes, we genotyped all known loci in a cohort of 43 WWS patients of varying geographical and ethnic origin. Surprisingly, we reached a molecular diagnosis for 40% of our patients and found mutations in POMT1, POMT2, FCMD and FKRP, many of which were novel alleles, but no mutations in POMGNT1 or LARGE. Notably, the FCMD gene was a more common cause of WWS than previously expected in the European/American subset of our cohort, including all Ashkenazi Jewish cases, who carried the same founder mutation.

High Incidence of Noonan Syndrome Features Including Short Stature and Pulmonic Stenosis in Patients carrying NF1 Missense Mutations Affecting p.Arg1809: Genotype–Phenotype Correlation

Neurofibromatosis type 1 (NF1) is one of the most frequent genetic disorders, affecting 1:3,000 worldwide. Identification of genotype–phenotype correlations is challenging because of the wide range clinical variability, the progressive nature of the disorder, and extreme diversity of the mutational spectrum. We report 136 individuals with a distinct phenotype carrying one of five different NF1 missense mutations affecting p.Arg1809. Patients presented with multiple café‐au‐lait macules (CALM) with or without freckling and Lisch nodules, but no externally visible plexiform neurofibromas or clear cutaneous neurofibromas were found. About 25% of the individuals had Noonan‐like features. Pulmonic stenosis and short stature were significantly more prevalent compared with classic cohorts (P < 0.0001). Developmental delays and/or learning disabilities were reported in over 50% of patients. Melanocytes cultured from a CALM in a segmental NF1‐patient showed two different somatic NF1 mutations, p.Arg1809Cys and a multi‐exon deletion, providing genetic evidence that p.Arg1809Cys is a loss‐of‐function mutation in the melanocytes and causes a pigmentary phenotype. Constitutional missense mutations at p.Arg1809 affect 1.23% of unrelated NF1 probands in the UAB cohort, therefore this specific NF1 genotype–phenotype correlation will affect counseling and management of a significant number of patients.

Newborn screening for Krabbe disease in New York State: the first eight years' experience

Purpose:Krabbe disease (KD) results from galactocerebrosidase (GALC) deficiency. Infantile KD symptoms include irritability, progressive stiffness, developmental delay, and death. The only potential treatment is hematopoietic stem cell transplantation. New York State (NYS) implemented newborn screening for KD in 2006.Methods:Dried blood spots from newborns were assayed for GALC enzyme activity using mass spectrometry, followed by molecular analysis for those with low activity (≤12% of the daily mean). Infants with low enzyme activity and one or more mutations were referred for follow-up diagnostic testing and neurological examination.Results:Of >1.9 million screened, 620 infants were subjected to molecular analysis and 348 were referred for diagnostic testing. Five had enzyme activities and mutations consistent with infantile KD and manifested clinical/neurodiagnostic abnormalities. Four underwent transplantation, two are surviving with moderate to severe handicaps, and two died from transplant-related complications. The significance of many sequence variants identified is unknown. Forty-six asymptomatic infants were found to be at moderate to high risk for disease.Conclusions:The positive predictive value of KD screening in NYS is 1.4% (5/346) considering confirmed infantile cases. The incidence of infantile KD in NYS is approximately 1 in 394,000, but it may be higher for later-onset forms.Genet Med 18 3, 239–248.

Induction of Gαq-specific Antisense RNA in Vivo Causes Increased Body Mass and Hyperadiposity

Transgenic BDF-1 mice harboring an inducible, tissue-specific transgene for RNA antisense to Gαq provide a model in which to study a loss-of-function mutant of Gαq in vivo Gαq deficiency induced in liver and white adipose tissue at birth produced increased body mass and hyperadiposity within 5 weeks of birth that persisted throughout adult life. Gαq-deficient adipocytes display reduced lipolytic responses, shown to reflect a newly discovered, α1-adrenergic regulation of lipolysis. This α1-adrenergic response via phosphoinositide hydrolysis and activation of protein kinase C is lacking in the Gαq loss-of-function mutants in vivo and provides a basis for the increased fat accumulation.

Clinical outcomes of children with abnormal newborn screening results for Krabbe disease in New York State

Background:Early infantile Krabbe disease is rapidly fatal, but hematopoietic stem cell transplantation (HSCT) may improve outcomes if performed soon after birth. New York State began screening all newborns for Krabbe disease in 2006.Methods:Infants with abnormal newborn screen results for Krabbe disease were referred to specialty-care centers. Newborns found to be at high risk for Krabbe disease underwent a neurodiagnostic battery to determine the need for emergent HSCT.Results:Almost 2 million infants were screened. Five infants were diagnosed with early infantile Krabbe disease. Three died, two from HSCT-related complications and one from untreated disease. Two children who received HSCT have moderate to severe developmental delays. Forty-six currently asymptomatic children are considered to be at moderate or high risk for development of later-onset Krabbe disease.Conclusions:These results show significant HSCT-associated morbidity and mortality in early infantile Krabbe disease and raise questions about its efficacy when performed in newborns diagnosed through newborn screening. The unanticipated identification of “at risk” children introduces unique ethical and medicolegal issues. New York’s experience raises questions about the risks, benefits, and practicality of screening newborns for Krabbe disease. It is imperative that objective assessments be made on an ongoing basis as additional states begin screening for this disorder.Genet Med 18 12, 1235–1243.

Screening for GALC to make neonatal diagnosis and initial neonatal stem cell treatment with umbilical cord blood

Lysosomal storage disorders represent a group of over 40 distinct genetic diseases with a total incidenceofapproximately1:7000births.Krabbe’s disease is one of these disorders, occuring as a result of greatly diminished or absent activity of the lysosomal enzyme b-galactocerebrosidase (GALC) (1). Its course is characterized by the progressive loss of central and peripheral myelin and by spasticity, dementia, and peripheral neuropathy. About 90% of Krabbe’s patients have an infantile course which is rapidly progressive and fatal within the first few years. The remainder of the group becomes symptomatic later in childhood or even as adults (2). The gene responsible for this disorder has been found and more than 40 mutations have been identified in patients with all clinical types of Krabbe. Homozygous mutations or two severe mutations will result in the infantile type. However, it is difficult to predict the phenotype of novel mutations or when mutations are found in the heterozygous state (3). Theoretic treatment plans for the lysosomal storage disorders have included enzyme replacement therapy (4), cell replacement therapy (5), drug therapy (6), gene therapy (7), bone marrow transplant (8) and hematopoietic stem cell transplant including umbilical cord stem cells (9). In Krabbe’s disease, reports have indicated a favorable clinical course following treatment in the late onset form of the disease (8) but little success following the diagnosis of symptomatic patients with the infantile form (10). In the manuscript by Caniglia et al., published in the October issue, the authors report on an infant with only minimal central nervous system (CNS) involvement who received an allogeneic bone marrow transplant at 4 months of age. In spite of positive engraftment, the infant continued to display neurologic deterioration and early death. The paper stresses the need to identify affected infants prior to the onset of any CNS involvement and points out the difficulty in achieving this goal. Currently, a work-up for GALC is initiated only after the presentation of clinical symptoms and confirmation of diagnosis is time-consuming. By the time of confirmation, the authors indicate that these cases would be too far advanced to be eligible for therapy. Except for cases with a family history of the disease, the presymptomatic detection of Krabbe’s disease will only be possible through early diagnosis as with a newborn screening program. Newborn screening was first introduced by Dr Guthrie in the 1960s for the detection of phenylketonuria. Diagnosis from dried blood spots on filter paper, known as Guthrie cards, is still used (11). Since that time, every state in the USA has adopted a newborn screening program although the disorders screened vary from state to state. Over the years the number of disorders which can be picked up by a screening technique have greatly increased. There have been numerous ethical debates over which disorders qualify for screening and what each state will offer. Tandem mass spectrometry (MS/MS) has become a key technology in the fields of biochemical genetics and newborn screening (12). The development of electrospray ionisation with MS/MS and associated automation of sample handling have allowed newborn screening for an ever growing number of disorders (13). Research in determination of oligosaccharides and glycolipids by tandem mass spectrometry has been underway to diagnose lysosomal disorders. A novel use of electrospray mass spectrometry to determine activity of galactocerebroside b-galactosidase by monitoring the change in molecular Pediatr Transplantation 2003: 7: 83–85

Genotype-Phenotype Correlation in NF1: Evidence for a More Severe Phenotype Associated with Missense Mutations Affecting NF1 Codons 844–848

Neurofibromatosis type 1 (NF1), a common genetic disorder with a birth incidence of 1:2,000–3,000, is characterized by a highly variable clinical presentation. To date, only two clinically relevant intragenic genotype-phenotype correlations have been reported for NF1 missense mutations affecting p.Arg1809 and a single amino acid deletion p.Met922del. Both variants predispose to a distinct mild NF1 phenotype with neither externally visible cutaneous/plexiform neurofibromas nor other tumors. Here, we report 162 individuals (129 unrelated probands and 33 affected relatives) heterozygous for a constitutional missense mutation affecting one of five neighboring NF1 codons—Leu844, Cys845, Ala846, Leu847, and Gly848—located in the cysteine-serine-rich domain (CSRD). Collectively, these recurrent missense mutations affect ∼0.8% of unrelated NF1 mutation-positive probands in the University of Alabama at Birmingham (UAB) cohort. Major superficial plexiform neurofibromas and symptomatic spinal neurofibromas were more prevalent in these individuals compared with classic NF1-affected cohorts (both p < 0.0001). Nearly half of the individuals had symptomatic or asymptomatic optic pathway gliomas and/or skeletal abnormalities. Additionally, variants in this region seem to confer a high predisposition to develop malignancies compared with the general NF1-affected population (p = 0.0061). Our results demonstrate that these NF1 missense mutations, although located outside the GAP-related domain, may be an important risk factor for a severe presentation. A genotype-phenotype correlation at the NF1 region 844–848 exists and will be valuable in the management and genetic counseling of a significant number of individuals.

Deficient activity of alanyl-tRNA synthetase underlies an autosomal recessive syndrome of progressive microcephaly, hypomyelination, and epileptic encephalopathy

Aminoacyl‐transfer RNA (tRNA) synthetases ligate amino acids to specific tRNAs and are essential for protein synthesis. Although alanyl‐tRNA synthetase (AARS) is a synthetase implicated in a wide range of neurological disorders from Charcot‐Marie‐Tooth disease to infantile epileptic encephalopathy, there have been limited data on their pathogenesis. Here, we report loss‐of‐function mutations in AARS in two siblings with progressive microcephaly with hypomyelination, intractable epilepsy, and spasticity. Whole‐exome sequencing identified that the affected individuals were compound heterozygous for mutations in AARS gene, c.2067dupC (p.Tyr690Leufs*3) and c.2738G>A (p.Gly913Asp). A lymphoblastoid cell line developed from one of the affected individuals showed a strong reduction in AARS abundance. The mutations decrease aminoacylation efficiency by 70%–90%. The p.Tyr690Leufs*3 mutation also abolished editing activity required for hydrolyzing misacylated tRNAs, thereby increasing errors during aminoacylation. Our study has extended potential mechanisms underlying AARS‐related disorders to include destabilization of the protein, aminoacylation dysfunction, and defective editing activity.