Rainer Rossi

Mutations in the gene encoding immunoglobulin μ-binding protein 2 cause spinal muscular atrophy with respiratory distress type 1

Classic spinal muscular atrophy (SMA) is caused by mutations in the telomeric copy of SMN1. Its product is involved in various cellular processes, including cytoplasmic assembly of spliceosomal small nuclear ribonucleoproteins, pre-mRNA processing and activation of transcription. Spinal muscular atrophy with respiratory distress (SMARD) is clinically and genetically distinct from SMA. Here we demonstrate that SMARD type 1 (SMARD1) results from mutations in the gene encoding immunoglobulin μ-binding protein 2 (IGHMBP2; on chromosome 11q13.2–q13.4). In six SMARD1 families, we detected three recessive missense mutations (exons 5, 11 and 12), two nonsense mutations (exons 2 and 5), one frameshift deletion (exon 5) and one splice donor-site mutation (intron 13). Mutations in mouse Ighmbp2 (ref. 14) have been shown to be responsible for spinal muscular atrophy in the neuromuscular degeneration (nmd) mouse, whose phenotype resembles the SMARD1 phenotype. Like the SMN1 product, IGHMBP2 colocalizes with the RNA-processing machinery in both the cytoplasm and the nucleus. Our results show that IGHMBP2 is the second gene found to be defective in spinal muscular atrophy, and indicate that IGHMBP2 and SMN share common functions important for motor neuron maintenance and integrity in mammals.

Diaphragmatic Spinal Muscular Atrophy with Respiratory Distress Is Heterogeneous, and One Form Is Linked to Chromosome 11q13-q21

To the Editor: Diaphragmatic spinal muscular atrophy (SMA) has been delineated as a variant of infantile SMA (SMA1 [MIM 253300]) (Mellins et al. 1974; Bertini et al. 1989). The most prominent symptoms are severe respiratory distress resulting from diaphragmatic paralysis with eventration shown on chest x-ray and predominant involvement of the upper limbs and distal muscles. In contrast to classic SMA1, in diaphragmatic SMA the upper spinal cord is more severely affected than the lower section. The pmn mouse presents with progressive motor neuronopathy and a disease that closely resembles diaphragmatic SMA (Schmalbruch et al. 1991). The pmn locus has been mapped to murine chromosome 13 (Brunialti et al. 1995). Here we report on nine patients from three families with diaphragmatic SMA following autosomal recessive inheritance. The diagnosis of diaphragmatic SMA was made on the basis of clinical criteria (Rudnik-Schoneborn et al. 1996). Family 1 is of Lebanese origin; family 2, German origin; and family 3, Italian origin. We obtained DNA samples from these families after receiving informed consent, in accordance with the Declaration of Helsinki. In family 1 (fig. 1A), the parents are first cousins. The first affected son died, at the age of 10 wk, of suspected sudden infant death syndrome (SIDS). One daughter presented, at the age of 6 wk, with feeding difficulties and progressive respiratory distress. Chest x-ray showed eventration of the diaphragm. Mechanical ventilation was initiated at the age of 8 wk. She developed progressive muscular atrophy with complete paralysis of the upper and lower limbs and mild contractures of the knee and ankle joints. Three other children, nonidentical twin daughters and the youngest daughter, died of respiratory failure—the twins at the age of 8 and 9 wk and the youngest daughter at the age of 8 wk. Autopsy specimens were taken from gastrocnemius muscle in both twins and from the upper spinal cord in one twin. Skeletal-muscle histology revealed neurogenic atrophy without signs of reinnervation. Ultrastructurally, the motor end plates lacked nerve terminals and showed postsynaptic degenerative changes characterized by deep invaginations. The diameter of anterior spinal roots was reduced in the upper spinal cord. The remaining motor neurons showed chromatolysis. These findings offer two different pathophysiological concepts: (1) degeneration of the anterior horn cells of the spinal cord with neurogenic muscular atrophy suggests dying-forward atrophy, and (2) presynaptic and postsynaptic signs of motor end-plate degeneration suggest dying-back atrophy. In family 2 (fig. 1B), the first child had severe muscular hypotonia and died, at the age of 9 wk, of cardiorespiratory failure. The third child has been mechanically ventilated since the age of 3 mo. In family 3 (fig. 1C), which has been reported in detail elsewhere (Novelli et al. 1995), the gene locus for SMA1, on chromosome 5q, has been excluded. Both affected sibs presented with respiratory insufficiency right after birth and with the typical signs of diaphragmatic SMA. Figure 1 Haplotypes in families with diaphragmatic SMA subtypes. A, Family 1 (Lebanese origin): age at onset, 6–10 wk. B, Family 2 (German origin): age at onset, 9–12 wk. C, Family 3 (Italian origin): onset at birth. Haplotype analysis indicated ... First, we confirmed that, in families 1 and 2, there is no linkage of the trait to markers of the SMA locus on 5q11.2-q13.3, as there is in family 3. Second, the orthologous regions corresponding to the murine pmn gene region on human chromosomes 1q and 7p were excluded as gene loci responsible for the disease (Grohmann et al. 1998). To locate the gene locus for diaphragmatic SMA, a whole-genome scan was undertaken in family 1. Microsatellite analysis was performed, by standard semiautomated methods, by an ABI 377-Sequencer, and the results were processed by GENESCAN software, as described elsewhere (Saar et al. 1997). The whole-genome linkage scan was performed with the use of 340 polymorphic fluorescence–labeled markers spaced at ∼10-cM intervals throughout the autosomal part of the genome. Subsequent fine mapping was performed with eight additional microsatellite markers. Markers were chosen from the Genethon final linkage map. Two-point parametric linkage analyses were performed with the LINKAGE package, version 5.2 (Lathrop and Lalouel 1984), under the following assumptions: a regular, fully penetrant autosomal recessive trait locus with a disease-allele frequency of .002 and no phenocopy rate, codominant marker loci with uniformly distributed allele frequencies, and standard recombination rates. Multipoint analysis was performed with the GENEHUNTER program, version 1.3 (Kruglyak et al. 1996). Genomewide linkage scanning of family 1 revealed linkage of diaphragmatic SMA only to markers on chromosome 11q13-q21. In the following, we name this subtype of diaphragmatic SMA “spinal muscular atrophy with respiratory distress” (SMARD). For the markers D11S1296, D11S4095, D11S901, D11S1358, and D11S1757, a maximum two-point LOD score of 3.16 at recombination fraction (θ) 0 was obtained. The two-point LOD scores for 13 markers on chromosome 11q are summarized in table 1. Haplotype analysis revealed a recombination event in individual 2.4 that placed the disease locus distal to marker D11S1883 (fig. 1A). The crossing-over in individual 2.1 placed the disease locus proximal to marker D11S917. Consistent with parental consanguinity, all affected siblings from family 1 were autozygous for all markers within the cosegregating segment. Multipoint linkage analysis with the use of 13 markers yielded a maximum LOD score of 3.86, which clearly places the disease locus between D11S1883 and D11S917 (Genethon map positions 68.5 cM and 100.9 cM). Table 1 LOD-Score Values at Standard Recombination Rates for Markers on Chromosome 11q in Lebanese Family 1 In family 2, the two affected sibs shared two identical parental haplotypes in the SMARD cosegregating segment on 11q13-q21, a finding that supports the assignment of the SMARD locus to this region (fig. 1B). In family 3, haplotype analysis was inconsistent with linkage to the markers tested (fig. 1C). Thus, this locus was excluded as being responsible for the disease in this family. Our finding that diaphragmatic SMA with onset at age 6–12 wk is linked to chromosome 11q markers in two apparently unrelated families from different countries (families 1 and 2) but that diaphragmatic SMA with onset at birth does not show such linkage (family 3) suggests that diaphragmatic SMA is both clinically and genetically heterogeneous. The prevalence of diaphragmatic SMA is unknown. However, in a series of >200 patients with early-onset SMA, ∼1% presented with diaphragmatic SMA and did not have a deletion of the survival motor-neuron gene (SMN) on chromosome 5q (Rudnik-Schoneborn et al. 1996). Considering the case history of the affected son from family 1 who had suspected SIDS, we presume that some of those infants with SIDS may possibly have been misdiagnosed. We are currently looking for further patients with SMARD, to refine the large cosegregating region on chromosome 11q.

Permissive hypercapnia in extremely low birthweight infants (PHELBI): a randomised controlled multicentre trial

BACKGROUND Tolerating higher partial pressure of carbon dioxide (pCO2) in mechanically ventilated, extremely low birthweight infants might reduce ventilator-induced lung injury and bronchopulmonary dysplasia. We aimed to test the hypothesis that higher target ranges for pCO2 decrease the rate of bronchopulmonary dysplasia or death. METHODS In this randomised multicentre trial, we recruited infants from 16 tertiary care perinatal centres in Germany with birthweight between 400 g and 1000 g and gestational age 23-28 weeks plus 6 days, who needed endotracheal intubation and mechanical ventilation within 24 h of birth. Infants were randomly assigned to either a high target or control group. The high target group aimed at pCO2 values of 55-65 mm Hg on postnatal days 1-3, 60-70 mm Hg on days 4-6, and 65-75 mm Hg on days 7-14, and the control target at pCO2 40-50 mmHg on days 1-3, 45-55 mm Hg on days 4-6, and 50-60 mm Hg on days 7-14. The primary outcome was death or moderate to severe bronchopulmonary dysplasia, defined as need for mechanical pressure support or supplemental oxygen at 36 weeks postmenstrual age. Cranial ultrasonograms were assessed centrally by a masked paediatric radiologist. This trial is registered with the ISRCTN registry, number ISRCTN56143743. RESULTS Between March 1, 2008, and July 31, 2012, we recruited 362 patients of whom three dropped out, leaving 179 patients in the high target and 180 in the control group. The trial was stopped after an interim analysis (n=359). The rate of bronchopulmonary dysplasia or death in the high target group (65/179 [36%]) did not differ significantly from the control group (54/180 [30%]; p=0·18). Mortality was 25 (14%) in the high target group and 19 (11%; p=0·32) in the control group, grade 3-4 intraventricular haemorrhage was 26 (15%) and 21 (12%; p=0·30), and the rate of severe retinopathy recorded was 20 (11%) and 26 (14%; p=0·36). INTERPRETATION Targeting a higher pCO2 did not decrease the rate of bronchopulmonary dysplasia or death in ventilated preterm infants. The rates of mortality, intraventricular haemorrhage, and retinopathy did not differ between groups. These results suggest that higher pCO2 targets than in the slightly hypercapnic control group do not confer increased benefits such as lung protection. FUNDING Deutsche Forschungsgemeinschaft.

Estimation of ifosfamide/cisplatinum-induced renal toxicity by urinary protein analysis.

Ifosfamide (IFO) chemotherapy has been reported to result in deToni-Debré-Fanconi syndrome in a minority of patients only, but evaluation of tubular transport capacities has identified a substantial number of patients as having subclinical tubular dysfunction. After completion of combination chemotherapy employing IFO (n=37) or IFO plus cisplatinum (CPL) (n=27), glomerular and tubular function was assessed in 64 patients by the urinary excretion of transferrin, IgG, albumin, α1-microglobulin (A1M) andN-acetyl-β-d-glucosaminidase. Sodium dodecyl sulphate polyacrylamide gel electrophoresis was performed in 21 patients. The determination of urinary marker proteins was compared with the glomerular filtration rate, the fractional phosphate and percent amino acid reabsorption. A reduced glomerular filtration rate was observed in 9.8% of patients. Tubular dysfunction was frequent, with a predominance of renal amino acid (57%) and A1M (48%) loss. IFO-mediated renal toxicity was dose dependent. CPL treatment resulted in significant enhancement of tubular toxicity induced by IFO, whereas concomitant gentamicin therapy did not affect tubular function. Measurement of urinary protein cannot replace other tests for tubular dysfunction in IFO-treated patients, because the spectrum of IFO-induced nephrotoxicity includes dysfunction of different and independent transport mechanisms of the proximal tubular system. Increased urinary A1M excretion is an important indicator of impaired tubular protein reabsorption.

Renal Fanconi syndrome: first sign of partial respiratory chain complex IV deficiency.

Abstract A 2-year-old boy who developed hypophosphatemic rickets without signs of muscular weakness or neurological disturbances is presented. Biochemical findings included hypophosphatemia, metabolic acidosis, hypouricemia, hyperphosphaturia, severe glucosuria, generalized hyperaminoaciduria, hypercalciuria, proteinuria with elevated excretion of IgG, transferrin, albumin and high levels of α-1-microglobulin. Urine concentration capacity and creatinine clearance were normal. Lactaturia without elevated levels of plasma lactate and a high urinary excretion of β-hydroxybutyrate were suggestive for mitochondriopathy. Partial deficiency of cytochrome c oxidase (complex IV of the respiratory chain) was found in skeletal muscle. A renal biopsy specimen demonstrated enlarged mitochondria with abnormal arborization and disorientation of the cristae in the proximal tubular cells. Reduced activity of mitochondrial cytochrome c oxidase in tubular cells could be demonstrated by ultracytochemistry. In conclusion, rickets due to the renal Fanconi syndrome can be the first clinical sign of mitochondrial cytopathies without extrarenal symptoms. Elevated excretion of lactate and ketone bodies in urine may serve as a diagnostic marker.

The factor V G1691A mutation is a risk for porencephaly: A case-control study

This study was initiated to investigate prothrombotic risk factors in children with porencephaly. 76 porencephalic and 76 healthy infants were investigated for factor V (FV) G1691A mutation, factor II G20210A variant, methylenetetrahydrofolate reductase (MTHFR) C677T genotype, lipoprotein (a), protein C, protein S, and antithrombin. Only the FV mutation (p = 0.005) and combinations of two or three different risk factors (p = 0.003) were significantly associated with porencephaly. These data give evidence that the FV G1691A mutation and a combination of prothromboic factors play a major role in the development of childhood porencephaly. Ann Neurol 2004.

Congenital Ichthyosis in Severe Type II Gaucher Disease with a Homozygous Null Mutation

This paper describes a neonate with type II Gaucher disease. The phenotype was unusually severe with congenital ichthyosis, hepatosplenomegaly, muscular hypotonia, myoclonus and respiratory failure. Electron microscopy of the skin revealed lamellar body contents in the stratum corneum interstices, appearances considered to be typical of type II Gaucher disease. The baby died from respiratory failure 1 month postpartum having made no neurological progress. Molecular analysis identified a previously not reported homozygous null mutation, c.1505G→A of the β-glucocerebrosidase gene.

Neurodevelopmental outcomes of extremely low birthweight infants randomised to different PCO2 targets: the PHELBI follow-up study

Background Tolerating higher partial pressures of carbon dioxide (PCO2) in mechanically ventilated extremely low birthweight infants to reduce ventilator-induced lung injury may have long-term neurodevelopmental side effects. This study analyses the results of neurodevelopmental follow-up of infants enrolled in a randomised multicentre trial. Methods Infants (n=359) between 400 and 1000 g birth weight and 23 0/7–28 6/7 weeks gestational age who required endotracheal intubation and mechanical ventilation within 24 hours of birth were randomly assigned to high PCO2 or to a control group with mildly elevated PCO2 targets. Neurodevelopmental follow-up examinations were available for 85% of enrolled infants using the Bayley Scales of Infant Development II, the Gross Motor Function Classification System (GMFCS) and the Child Development Inventory (CDI). Results There were no differences in body weight, length and head circumference between the two PCO2 target groups. Median Mental Developmental Index (MDI) values were 82 (60–96, high target) and 84 (58–96, p=0.79). Psychomotor Developmental Index (PDI) values were 84 (57–100) and 84 (65–96, p=0.73), respectively. Moreover, there was no difference in the number of infants with MDI or PDI <70 or <85 and the number of infants with a combined outcome of death or MDI<70 and death or PDI<70. No differences were found between results for GMFCS and CDI. The risk factors for MDI<70 or PDI<70 were intracranial haemorrhage, bronchopulmonary dysplasia, periventricular leukomalacia, necrotising enterocolitis and hydrocortisone treatment. Conclusions A higher PCO2 target did not influence neurodevelopmental outcomes in mechanically ventilated extremely preterm infants. Adjusting PCO2 targets to optimise short-term outcomes is a safe option. Trial registration number ISRCTN56143743.

Influence of PCO2 Control on Clinical and Neurodevelopmental Outcomes of Extremely Low Birth Weight Infants

Background: Levels or fluctuations in the partial pressure of CO2 (PCO2) may affect outcomes for extremely low birth weight infants. Objectives: In an exploratory analysis of a randomized trial, we hypothesized that the PCO2 values achieved could be related to significant outcomes. Methods: On each treatment day, infants were divided into 4 groups: relative hypocapnia, normocapnia, hypercapnia, or fluctuating PCO2. Ultimate assignment to a group for the purpose of this analysis was made according to the group in which an infant spent the most days. Statistical analyses were performed with analysis of variance (ANOVA), the Kruskal-Wallis test, the χ2 test, and the Fisher exact test as well as by multiple logistic regression. Results: Of the 359 infants, 57 were classified as hypocapnic, 230 as normocapnic, 70 as hypercapnic, and 2 as fluctuating PCO2. Hypercapnic infants had a higher average product of mean airway pressure and fraction of inspired oxygen (MAP × FiO2). For this group, mortality was higher, as was the likelihood of having moderate/severe bronchopulmonary dysplasia (BPD), necrotizing enterocolitis (NEC), and poorer neurodevelopment. Multiple logistic regression analyses showed an increased risk for BPD or death associated with birth weight (p < 0.001) and MAP × FiO2 (p < 0.01). The incidence of adverse neurodevelopment was associated with birth weight (p < 0.001) and intraventricular hemorrhage (IVH; p < 0.01). Conclusions: Birth weight and respiratory morbidity, as measured by MAP × FiO2, were the most predictive of death or BPD and NEC, whereas poor neurodevelopmental outcome was associated with low birth weight and IVH. Univariate models also identified PCO2. Thus, hypercapnia seems to reflect greater disease severity, a likely contributor to differences in outcomes.