Stuart K. Shapira

Chromosome 1p36 Deletions: The Clinical Phenotype and Molecular Characterization of a Common Newly Delineated Syndrome

Deletions of the distal short arm of chromosome 1 (1p36) represent a common, newly delineated deletion syndrome, characterized by moderate to severe psychomotor retardation, seizures, growth delay, and dysmorphic features. Previous cytogenetic underascertainment of this chromosomal deletion has made it difficult to characterize the clinical and molecular aspects of the syndrome. Recent advances in cytogenetic technology, particularly FISH, have greatly improved the ability to identify 1p36 deletions and have allowed a clearer definition of the clinical phenotype and molecular characteristics of this syndrome. We have identified 14 patients with chromosome 1p36 deletions and have assessed the frequency of each phenotypic feature and clinical manifestation in the 13 patients with pure 1p36 deletions. The physical extent and parental origin of each deletion were determined by use of FISH probes on cytogenetic preparations and by analysis of polymorphic DNA markers in the patients and their available parents. Clinical examinations revealed that the most common features and medical problems in patients with this deletion syndrome include large anterior fontanelle (100%), motor delay/hypotonia (92%), moderate to severe mental retardation (92%), growth delay (85%), pointed chin (80%), eye/vision problems (75%), seizures (72%), flat nasal bridge (65%), clinodactyly and/or short fifth finger(s) (64%), low-set ear(s) (59%), ear asymmetry (57%), hearing deficits (56%), abusive behavior (56%), thickened ear helices (53%), and deep-set eyes (50%). FISH and DNA polymorphism analysis showed that there is no uniform region of deletion but, rather, a spectrum of different deletion sizes with a common minimal region of deletion overlap.

Clinical, cytogenetic, and molecular characterization of seven patients with deletions of chromosome 22q13. 3

We have studied seven patients who have chromosome 22q13.3 deletions as revealed by high-resolution cytogenetic analysis. Clinical evaluation of the patients revealed a common phenotype that includes generalized developmental delay, normal or accelerated growth, hypotonia, severe delays in expressive speech, and mild facial dysmorphic features. Dosage analysis using a series of genetically mapped probes showed that the proximal breakpoints of the deletions varied over approximately 13.8 cM, between loci D22S92 and D22S94. The most distally mapped locus, arylsulfatase A (ARSA), was deleted in all seven patients. Therefore, the smallest region of overlap (critical region) extends between locus D22S94 and a region distal to ARSA, a distance of > 25.5 cM.

Loss of the Potassium Channel β‐Subunit Gene, KCNAB2, Is Associated with Epilepsy in Patients with 1p36 Deletion Syndrome

Summary:  Purpose: Clinical features associated with chromosome 1p36 deletion include characteristic craniofacial abnormalities, mental retardation, and epilepsy. The presence and severity of specific phenotypic features are likely to be correlated with loss of a distinct complement of genes in each patient. We hypothesize that hemizygous deletion of one, or a few, critical gene(s) controlling neuronal excitability is associated with the epilepsy phenotype. Because ion channels are important determinants of seizure susceptibility and the voltage‐gated K+ channel β‐subunit gene, KCNAB2, has been localized to 1p36, we propose that deletion of this gene may be associated with the epilepsy phenotype.

DNA Rearrangements on Both Homologues of Chromosome 17 in a Mildly Delayed Individual with a Family History of Autosomal Dominant Carpal Tunnel Syndrome

Disorders known to be caused by molecular and cytogenetic abnormalities of the proximal short arm of chromosome 17 include Charcot-Marie-Tooth disease type 1A (CMT1A), hereditary neuropathy with liability to pressure palsies (HNPP), Smith-Magenis syndrome (SMS), and mental retardation and congenital anomalies associated with partial duplication of 17p. We identified a patient with multifocal mononeuropathies and mild distal neuropathy, growth hormone deficiency, and mild mental retardation who was found to have a duplication of the SMS region of 17p11.2 and a deletion of the peripheral myelin protein 22 (PMP22) gene within 17p12 on the homologous chromosome. Further molecular analyses reveal that the dup(17)(p11.2p11.2) is a de novo event but that the PMP22 deletion is familial. The family members with deletions of PMP22 have abnormalities indicative of carpal tunnel syndrome, documented by electrophysiological studies prior to molecular analysis. The chromosomal duplication was shown by interphase FISH analysis to be a tandem duplication. These data indicate that familial entrapment neuropathies, such as carpal tunnel syndrome and focal ulnar neuropathy syndrome, can occur because of deletions of the PMP22 gene. The co-occurrence of the 17p11.2 duplication and the PMP22 deletion in this patient likely reflects the relatively high frequency at which these abnormalities arise and the underlying molecular characteristics of the genome in this region.

Molecular basis of phenotypic variation in patients with argininemia

Argininemia is an autosomal recessive disorder caused by a deficiency in the liver-type arginase enzyme. Clinical manifestations include progressive spastic diplegia and mental retardation. While the quality of life can severely deteriorate in most such patients, some do show remarkable improvement in neurological symptoms while on controlled diets. We examined the thesis that differences in clinical responses to dietary treatment are based on molecular heterogeneity in mutant arginase alleles. Genomic DNAs from 11 patients with argininemia were examined using the polymerase chain reaction, cloning, and sequencing. Nine mutations representing 21/22 mutant alleles were identified in 11 patients with argininemia, and four of these mutations were expressed in vitro to determine the severity of enzymatic defects. We found that these mutations accounted for 64% of the mutant alleles in our patients. Based on findings in vitro expression tests, the mutations can be considered either severe or moderate. Patients with at least one moderate mutant allele responded well to dietary treatment; concentrations of plasma arginine were controlled within 300 μM. In contrast, patients with two severely mutated alleles did not respond to dietary treatment and plasma arginine was over 400 μM. Argininemia is heterogeneous at the molecular level. The degree of clinical improvement during dietary treatment is reflected in the concentration of arginine in plasma, as a measure of metabolic control. Plasma arginine levels during treatment is reflected in the concentration of arginine in plasma, as a measure of metabolic control. Plasma arginine levels during treatment correlated with types of molecular defects in the arginase genes.

Inherited duplication Xq27-qter at Xp22.3 in severely affected males: Molecular cytogenetic evaluation and clinical description in three unrelated families

We describe the clinical phenotype in four males from three families with duplication (X)(qter-->q27::p22.3-->qter). This is an unusual duplication of the distal long arm segment, Xq27-qter, onto the distal short arm of the X chromosome at Xp22.3, as shown by fluorescent in situ hybridization analysis with multiple X-specific probes. The patients are young male offspring of three unrelated, phenotypically normal carrier women. The affected males have similar clinical manifestations including severe growth retardation and developmental delay, severe axial hypotonia, and minor anomalies. Such clinical similarity in three unrelated families demonstrates that this chromosome abnormality results in a new and distinct clinical phenotype. Replication studies, performed on two of the mothers, provided evidence that inactivation of the abnormal X chromosome permitted the structural abnormality to persist in these families for a generation or more in females without phenotypic expression.

Evaluation of Immunization Rates and Safety Among Children With Inborn Errors of Metabolism

BACKGROUND: Children with inherited metabolic disorders are a potential high-risk group for vaccine-preventable diseases, yet information regarding immunization rates and vaccine safety within this population is limited. METHODS: Using Northern California Kaiser Permanentes electronic medical record, we identified children with inborn errors of metabolism from 1990 to 2007. We assessed immunization rates among infants with inborn errors of metabolism born at Northern California Kaiser Permanente matched to healthy infants (1 to 20), comparing both vaccines received by 2 years of age and age at vaccination. We assessed postvaccination adverse events among children up to 18 years old with inborn errors of metabolism, separately comparing emergency-department visits and hospitalizations during postvaccine days 0 to 30 (primary) and days 0 to 14 (secondary). RESULTS: Comparing infants with inborn errors of metabolism (n = 77) versus matched control subjects (n = 1540), similar proportions were up to date for vaccines at 2 years of age, and there was no evidence of delay in receipt of recommended vaccines during the first year. Vaccination of children with inborn errors of metabolism (n = 271) was not associated with any significant increase in emergency-department visits or hospitalizations during the 30 days after vaccination. Secondary analyses suggested that there may be increased rates of hospitalizations 2 weeks after vaccination for the sickest 1- to 4-year-old children. CONCLUSIONS: Children with inborn errors of metabolism at Northern California Kaiser Permanente received vaccines on the same immunization schedule as healthy infants. Immunization was not associated with increased risk for serious adverse events during the month after vaccination, providing overall reassurance that routine vaccination of children with inborn errors of metabolism does not result in adverse effects.

Mitochondrial DNA Depletion Associated With Partial Complex II and IV Deficiencies and 3-Methylglutaconic Aciduria

We report a patient with mitochondrial DNA depletion, partial complex II and IV deficiencies, and 3-methylglutaconic aciduria. Complex II deficiency has not been previously observed in mitochondrial DNA depletion syndromes. The observation of 3-methylglutaconic and 3-methylglutaric acidurias may be a useful indicator of a defect in respiratory chain function caused by mitochondrial DNA depletion. (J Child Neurol 2001;16:136-138).

Future Research Directions to Identify Causes of the Increasing Incidence Rate of Congenital Hypothyroidism in the United States

A workshop to evaluate the reported increasing trend in the incidence rate of primary congenital hypothyroidism (CH) identified by newborn screening was held February 27 and 28, 2008, in Atlanta, Georgia, and was sponsored by the Centers for Disease Control and Prevention, the Health Resources and Services Administration, and the National Newborn Screening and Genetics Resource Center. Through a series of presentations and discussions, this group of experts considered a variety of factors that could be contributing to the perceived increasing trend of the CH-incidence rate, the gaps in knowledge that need to be overcome to identify the causes of the observed trend, and possible future research activities that might resolve the uncertainties surrounding the increasing incidence rate of CH in the United States. On the basis of these discussions, workshop participants concluded that the initial focus of future efforts should be to determine if the increasing CH-incidence rate persists once there is standardization of the diagnostic criteria for the classification of CH versus transient hypothyroidism. In discussions, workshop participants suggested that if the increasing incidence rate of CH could not be explained by definitional issues, then future research could focus on the identification and evaluation of risk factors for CH that might be changing among the US population and, thus, contributing to the observed increasing incidence rate of CH.

Normal expression of the Fanconi anemia proteins FAA and FAC and sensitivity to mitomycin C in two Patients with Seckel syndrome

Seckel syndrome is a rare autosomal recessive disorder. The classical presentation includes pre- and postnatal growth deficiency, mental retardation, and characteristic facial appearance. There have been several reports of associated hematological abnormalities and chromosomal breakage, findings suggestive of Fanconi anemia (FA). We tested for these findings in two Arabic patients with this syndrome. We compared the growth profile of lymphoblastoid cells from our patients and their parents with the FA group A cell line HSC72 in the presence and absence of mitomycin C (MMC). By Western analysis, we also determined the expression of FAA and FAC, two FA disease gene products that together account for approximately 80% of FA. Unlike HSC72 cells, cells from the patients were resistant to MMC, and both FAA and FAC proteins were expressed at similar levels in all cell lines. There is an increasing recognition of clinical variability and perhaps genetic heterogeneity in Seckel syndrome. Our results demonstrate that cross-link sensitivity comparable to FA is not a uniform finding in patients with Seckel syndrome.