Gene deletion patterns in spinal muscular atrophy patients with different clinical phenotypes

Clinical and Genetic Study of Algerian Patients with Spinal Muscular Atrophy

Spinal muscular atrophy (SMA) is the second most common lethal autosomal recessive disorder. It is divided into the acute Werdnig-Hoffmann disease (type I), the intermediate form (type II), the Kugelberg-Welander disease (type III), and the adult form (type IV). The gene involved in all four forms of SMA, the so-called survival motor neuron (SMN) gene, is duplicated, with a telomeric (tel SMN or SMN1) and a centromeric copy (cent SMN or SMN2). SMN1 is homozygously deleted in over 95% of SMA patients. Another candidate gene in SMA is the neuronal apoptosis inhibitory protein (NAIP) gene; it shows homozygous deletions in 45-67% of type I and 20-42% of type II/type III patients. Here we studied the SMN and NAIP genes in 92 Algerian SMA patients (20 type I, 16 type II, 53 type III, and 3 type IV) from 57 unrelated families, using a semiquantitative PCR approach. Homozygous deletions of SMN1 exons 7 and/or 8 were found in 75% of the families. Deletions of exon 4 and/or 5 of the NAIP gene were found in around 25%. Conversely, the quantitative analysis of SMN2 copies showed a significant correlation between SMN2 copy number and the type of SMA.

Noninvasive Ventilation in Children with Spinal Muscular Atrophy Types 1 and 2

OBJECTIVE

Our aim was to assess the efficacy of noninvasive ventilation (NIV) for the treatment of thoracoabdominal asynchrony during sleep in children with spinal muscular atrophy (SMA) types 1 and 2.

DESIGN

Nine subjects underwent assessment for sleep apnea/hypopnea index (AHI), mean oxyhemoglobin saturation (SpO2), oxygen desaturation index, transcutaneous carbon dioxide tension (tcpCO2), and mean phase angle during sleep as a measure of thoracoabdominal coordination. A second sleep study was performed with use of NIV.

RESULTS

The nine patients (7 mos of age, range 2-33) had a baseline AHI of 2.1 events per hour (range 0.5-55.8), oxygen desaturation index of 3.7 events per hour (range 1.6-46.1), mean tcpCO2 of 46 mm Hg (range 37-60), and phase angle of 127 degrees (range 72.7-151.7). Comparing baseline and NIV sleep studies, we found significant improvement in oxygen desaturation index (P < 0.010), mean tcpCO2 (P < 0.001), and phase angle (P < 0.001). For five patients, phase-angle improvement became significant when using high-span bilevel positive airway pressure (PAP).

CONCLUSIONS

NIV improved sleep breathing parameters and thoracoabdominal coordination during sleep in SMA types 1 and 2. Phase-angle improvement correlated with bilevel PAP pressures. Phase angle may be useful for the evaluation and monitoring of therapeutic interventions such as NIV.

Sleep-Disordered Breathing in Spinal Muscular Atrophy Types 1 and 2

OBJECTIVE

Our aim was to assess the respiratory pattern during sleep in patients affected by spinal muscular atrophy types 1 and 2 and to compare their apnea-hypopnea indices with those of controls.

DESIGN

All consecutively referred patients underwent polysomnography. Sleep stages were defined as either wake, quiet sleep (QS), or active sleep (AS). As measures of thoracoabdominal coordination, we measured: phase angle during QS and AS (Ph Angle QS and AS), phase relation during inspiration and expiration during QS and AS: (Ph RIB QS, Ph RIB AS, Ph REB QS; Ph REB AS) and the apnea-hypopnea index.

RESULTS

The 14 consecutively referred infants and small children (age, 11.7 +/- 11.4 mos) showed a higher apnea-hypopnea index (P < 0.001), Ph Angle QS (P < 0.001), Ph Angle AS (P < 0.001), Ph RIB QS (P < 0.001), Ph RIB AS (P < 0.001), Ph REB QS (P < 0.001), and Ph REB AS (P < 0.001) compared with 28 healthy controls (age, 10.1 +/- 8.9 mos).

CONCLUSIONS

Patients affected by types 1 and 2 spinal muscular atrophy had significantly higher apnea-hypopnea indices than controls. Thoracoabdominal asynchrony was present during the inspiratory and expiratory phases in both quiet and active sleep. Measures of thoracoabdominal coordination may be useful for the evaluation and monitoring of therapeutic interventions for these patients.

Regulation of alternative RNA splicing by exon definition and exon sequences in viral and mammalian gene expression

Intron removal from a pre-mRNA by RNA splicing was once thought to be controlled mainly by intron splicing signals. However, viral and other eukaryotic RNA exon sequences have recently been found to regulate RNA splicing, polyadenylation, export, and nonsense-mediated RNA decay in addition to their coding function. Regulation of alternative RNA splicing by exon sequences is largely attributable to the presence of two major cis-acting elements in the regulated exons, the exonic splicing enhancer (ESE) and the suppressor or silencer (ESS). Two types of ESEs have been verified from more than 50 genes or exons: purine-rich ESEs, which are the more common, and non-purine-rich ESEs. In contrast, the sequences of ESSs identified in approximately 20 genes or exons are highly diverse and show little similarity to each other. Through interactions with cellular splicing factors, an ESE or ESS determines whether or not a regulated splice site, usually an upstream 3' splice site, will be used for RNA splicing. However, how these elements function precisely in selecting a regulated splice site is only partially understood. The balance between positive and negative regulation of splice site selection likely depends on the cis-element's identity and changes in cellular splicing factors under physiological or pathological conditions.

Regulation of alternative RNA splicing by exon definition and exon sequences in viral and mammalian gene expression

Intron removal from a pre-mRNA by RNA splicing was once thought to be controlled mainly by intron splicing signals. However, viral and other eukaryotic RNA exon sequences have recently been found to regulate RNA splicing, polyadenylation, export, and nonsense-mediated RNA decay in addition to their coding function. Regulation of alternative RNA splicing by exon sequences is largely attributable to the presence of two major cis-acting elements in the regulated exons, the exonic splicing enhancer (ESE) and the suppressor or silencer (ESS). Two types of ESEs have been verified from more than 50 genes or exons: purine-rich ESEs, which are the more common, and non-purine-rich ESEs. In contrast, the sequences of ESSs identified in approximately 20 genes or exons are highly diverse and show little similarity to each other. Through interactions with cellular splicing factors, an ESE or ESS determines whether or not a regulated splice site, usually an upstream 3' splice site, will be used for RNA splicing. However, how these elements function precisely in selecting a regulated splice site is only partially understood. The balance between positive and negative regulation of splice site selection likely depends on the cis-element's identity and changes in cellular splicing factors under physiological or pathological conditions.

Birc1e is the gene within the Lgn1 locus associated with resistance to Legionella pneumophila

In inbred mouse strains, permissiveness to intracellular replication of Legionella pneumophila is controlled by a single locus (Lgn1), which maps to a region within distal Chromosome 13 that contains multiple copies of the gene baculoviral IAP repeat-containing 1 (Birc1, also called Naip; refs. 1-3). Genomic BAC clones from the critical interval were transferred into transgenic mice to functionally complement the Lgn1-associated susceptibility of A/J mice to L. pneumophila. Here we report that two independent BAC clones that rescue susceptibility have an overlapping region of 56 kb in which the entire Lgn1 transcript must lie. The only known full-length transcript coded in this region is Birc1e (also called Naip5).

Spinal muscular atrophy in black South Africans: concordance with the universal SMN1 genotype

Only one study has reported on the genetic basis of spinal muscular atrophy (SMA) in South African subjects. This was conducted in the Johannesburg region and has suggested that black South Africans only (indigenous Africans) differ from the norm. We have explored this further by DNA studies in 30 unrelated and racially diverse patients who reside in the Western Cape, and who were assessed as SMA subjects according to the internationally accepted inclusion criteria for SMA. These subjects were seen at the neurology clinic at Red Cross Children's Hospital in Cape Town during the period 1980-2001. Four had the type 1 form of SMA, 16 had type 2 and 10 had type 3. All patients were found to be homozygous for the loss of either exon 7 or exons 7 and 8 of the SMN1 gene. Six additional patients had anterior horn cell disease but were negative for the SMN1 gene deletion. All six had exclusion features listed in the international guidelines. This study shows that all patients from the Western Cape, which included 12 black South Africans, are no different genetically or phenotypically from the internationally recognized form of typical SMA.