Reduced sodium/proton exchanger NHE3 activity causes congenital sodium diarrhea

Congenital sodium diarrhea (CSD) refers to an intractable diarrhea of intrauterine onset with high fecal sodium loss. CSD is clinically and genetically heterogeneous. Syndromic CSD is caused by SPINT2 mutations. While we recently described four cases of the non-syndromic form of CSD that were caused by dominant activating mutations in intestinal receptor guanylate cyclase C (GC-C), the genetic cause for the majority of CSD is still unknown. Therefore, we aimed to determine the genetic cause for non-GC-C non-syndromic CSD in 18 patients from 16 unrelated families applying whole-exome sequencing and/or chromosomal microarray analyses and/or direct Sanger sequencing. SLC9A3 missense, splicing and truncation mutations, including an instance of uniparental disomy, and whole-gene deletion were identified in nine patients from eight families with CSD. Two of these nine patients developed inflammatory bowel disease (IBD) at 4 and 16 years of age. SLC9A3 encodes Na(+)/H(+) antiporter 3 (NHE3), which is the major intestinal brush-border Na(+)/H(+) exchanger. All mutations were in the NHE3 N-terminal transport domain, and all missense mutations were in the putative membrane-spanning domains. Identified SLC9A3 missense mutations were functionally characterized in plasma membrane NHE null fibroblasts. SLC9A3 missense mutations compromised NHE3 activity by reducing basal surface expression and/or loss of basal transport function of NHE3 molecules, whereas acute regulation was normal. This study identifies recessive mutations in NHE3, a downstream target of GC-C, as a cause of CSD and implies primary basal NHE3 malfunction as a predisposition for IBD in a subset of patients.

Molecular and clinical characterization of the myopathic form of mitochondrial DNA depletion syndrome caused by mutations in the thymidine kinase (TK2) gene

Mitochondrial DNA (mtDNA) depletion syndromes (MDSs) are a clinically and molecularly heterogeneous group of mitochondrial cytopathies characterized by severe mtDNA copy number reduction in affected tissues. Clinically, MDSs are mainly categorized as myopathic, encephalomyopathic, hepatocerebral, or multi-systemic forms. To date, the myopathic form of MDS is mainly caused by mutations in the TK2 gene, which encodes thymidine kinase 2, the first and rate limiting step enzyme in the phosphorylation of pyrimidine nucleosides. We analyzed 9 unrelated families with 11 affected subjects exhibiting the myopathic form of MDS, by sequencing the TK2 gene. Twelve mutations including 4 novel mutations were detected in 9 families. Skeletal muscle specimens were available from 7 out of 11 subjects. Respiratory chain enzymatic activities in skeletal muscle were measured in 6 subjects, and enzymatic activities were reduced in 3 subjects. Quantitative analysis of mtDNA content in skeletal muscle was performed in 5 subjects, and marked mtDNA content reduction was observed in each. In addition, we outline the molecular and clinical characteristics of this syndrome in a total of 52 patients including those previously reported, and a total of 36 TK2 mutations are summarized. Clinically, hypotonia and proximal muscle weakness are the major phenotypes present in all subjects. In summary, our study expands the molecular and clinical spectrum associated with TK2 deficiency.

Pregnancy of a patient with multiple Acyl-CoA dehydrogenation deficiency (MADD)

We describe the pregnancy of a patient of French-Canadian descent with multiple Acyl-CoA dehydrogenation deficiency (MADD). The proband was found to harbor a previously reported homozygous missense mutation on EFTDH gene (p.Pro534Leu:c.1601C>T) confirming the biochemical diagnosis of MADD. This mutation was not found in 50 controls from the same ethnic background. The clinical and molecular information of all patients with ETFDH mutations reported in the literature up-to-date are summarized.

A novel syndrome of mandibular hypoplasia, deafness, and progeroid features associated with lipodystrophy, undescended testes, and male hypogonadism

CONTEXT

Mandibuloacral dysplasia (MAD) is an autosomal recessive progeroid disorder associated with type A (partial) or B (generalized) lipodystrophy and is due to mutations in lamin A/C (LMNA) or zinc metalloproteinase (ZMPSTE24) genes.

OBJECTIVE

The objective of the study was to report a novel syndrome with some overlapping features with MAD.

RESULTS

We report seven patients with mandibular hypoplasia, deafness, progeroid features (MDP), and associated lipodystrophy. These patients have similar features to MAD patients such as hypoplastic mandible, beaked nose, stiff joints, and sclerodermatous skin. However, the patients did not harbor any disease causing variants in LMNA or ZMPSTE24 and showed distinct characteristics such as sensorineural hearing loss and absence of clavicular hypoplasia and acroosteolysis. All males with MDP had undescended testes and were hypogonadal. One adult female showed lack of breast development. Skinfold thickness, dual-energy X-ray absorptiometry and whole-body magnetic resonance imaging for body fat distribution revealed a lack of lipodystrophy in a prepubertal female but a progressive loss of sc fat presenting with partial lipodystrophy in young adults and generalized lipodystrophy in older patients.

CONCLUSIONS

Patients with MDP syndrome have a few overlapping but some distinct clinical features as compared with MAD, suggesting that it is a novel syndrome. The molecular basis of MDP syndrome remains to be elucidated.

Heparin cofactor II-thrombin complex: a biomarker of MPS disease

The mucopolysaccharidoses are a group of lysosomal storage disorders caused by defects in the degradation of glycosaminoglycans. Each disorder is characterized by progressive multi-system disease with considerable clinical heterogeneity. The clinical heterogeneity of these disorders is thought to be related to the degree of the metabolic block in glycosaminoglycan degradation which in turn is related to the underlying mutation at the respective locus. There are currently no objective means other than longitudinal clinical observation, or the detection of a recurrent genetic mutation to accurately predict the clinical course for an individual patient, particularly when diagnosed early. In addition, there are no specific disease biomarkers that reflect the total body burden of disease. The lack of specific biomarkers has made monitoring treatment responses and predicting disease course difficult in these disorders. The recent introduction of enzyme replacement therapy for MPS I, II, and VI highlights the need for objective measures of disease burden and disease responsiveness. We show that serum levels of heparin cofactor II-thrombin complex is a reliable biomarker of the mucopolysaccharidoses. Untreated patients have serum levels that range from 3- to 112-fold above control values. In a series of patients with varying severity of mucopolysaccharidosis I, the serum complex concentration was reflective of disease severity. In addition, serum heparin cofactor II-thrombin levels showed responsiveness to various treatment regimens. We propose that serum levels of heparin cofactor II-thrombin complex may provide an important assessment and monitoring tool for patients with mucopolysaccharidosis.

Importance of dressing removal before radiolabeled WBC imaging for musculoskeletal infection

Leukocyte imaging performed with in-111 or Tc-99m is gaining widespread acceptance as a method for detection of osteomyelitis associated with soft tissue injury or infection. The authors present three cases in which initial imaging was suggestive of a focal infectious process in bone and soft tissue. However, repeat imaging after the removal of wound dressings, which revealed sero-sanguineous discharge in all cases, resulted in a scan appearance that was much less remarkable for focal radiotracer accumulation in the bone. The authors conclude that accumulation of labeled WBCs in wound discharge can result in scans that are false-positive for osteomyelitis. Therefore, the authors recommend that wounds should be cleaned and dressings changed before imaging in order to avoid scans that are false-positive for osteomyelitis.

Fast stress and rest acquisitions for technetium-99m-sestamibi separate-day SPECT

Abbreviated acquisition protocols were designed for stress and rest to decrease stress and rest SPECT image acquisition times but maintain the high count density of 99mTc-sestamibi separate-day cardiac images.

METHODS

Scan findings were compared visually and quantitatively with standard SPECT for 12 rest and 32 stress patient studies.

RESULTS

Of 29 stress defects detected by standard SPECT, 27 were present with the fast technique; of 8 resting SPECT defects, all were detected with fast SPECT. Two stress and no resting false-positive defects occurred with fast SPECT. Linear correlations (r) between standard and fast quantitative defect extent and severity were 0.76 and 0.86, respectively for stress SPECT, and 0.88 and 0.96 for rest SPECT. Stress fast defects were slightly less severe (p = 0.02) than those observed using standard acquisition.

CONCLUSION

We conclude that these fast protocols for separate-day 99mTc-MIBI SPECT accurately detect and characterize perfusion defects and provide a means to improve patient tolerance and increase laboratory throughput.

Simultaneous biplane first-pass radionuclide angiocardiography using a scintillation camera with two perpendicular detectors

Generally performed in a single anterior or right anterior oblique (RAO) view, first-pass radionuclide angiocardiography (RNA) is limited due to its inability to evaluate septal and posterior wall motion.

METHODS

Thirty-five patients undergoing stress/rest sestamibi SPECT (22 mCi/22 mCi 2-day protocol) underwent biplane RNA at the time of resting injection. The stress SPECT images (acquired with the patient at rest) were ECG-gated to evaluate resting regional myocardial wall thickening. By this means wall motion assessed by RNA was compared to the presence of a resting SPECT perfusion defect accompanied by a localized decrease in wall thickening.

RESULTS

In 16 patients in whom both resting perfusion and wall thickening were normal one demonstrated apical hypokinesis by RNA in the RAO view. In the other 29 patients, a total of 58 resting segmental perfusion defects with abnormal wall thickening were present (12 anterior, 13 inferior, 14 apical, 11 septal and 8 posterolateral). Wall motion abnormalities were detected in all these patients and in 57/58 segments (98%) by biplane RNA. Septal and posterolateral wall motion abnormalities were detected in only the LAO RNA study. In three patients, wall motion abnormalities were detected by LAO imaging only. Of the remaining 87 normally perfused segments in these 29 patients, RNA wall motion was normal in 85. Two posterolateral segments demonstrated apparent hypokinesis, probably due to left atrial overlap in the LAO projection.

CONCLUSION

Simultaneous biplane RNA accurately detects wall motion abnormalities frequently missed by single-plane RAO imaging.

Genetic homogeneity at the Friedreich ataxia locus on chromosome 9

Classical Friedreich ataxia, a progressive, neurodegenerative disorder involving both the central and peripheral nervous systems, has been subclassified according to the observed clinical heterogeneity. The variations in the age at onset and in the spectrum and severity of symptoms have previously been interpreted as evidence of genetic heterogeneity. We have studied the linkage between the disorder and closely linked DNA markers in families of distinct ethnic origins, including the "typical" French-Canadians and the Acadian population of Louisiana. The disease in these two populations, both of continental French origin, has a very similar initial clinical picture. However, a marked difference in the rate of progression of the obligatory symptoms after 10 years of apparent disease is observed. A total of 553 individuals from 80 families with 202 affected members have been typed with the chromosome 9 marker MCT112, which we have previously shown to be closely linked to the disease locus. Evidence for linkage was observed in all families with the generation of a combined total lod score of 25.09 at a recombination fraction of theta = .00, providing strong evidence for genetic homogeneity at this locus for the classical form of this disease.

Differences in the damage caused by glaze ice on codominant Acer saccharum and Fagus grandifolia

A severe glaze ice storm had greater destructive impact on Fagus grandifolia than on codominant Acer saccharum trees in a mature southern Quebec forest. Both the numbers and total biomass of major branches lost by beech were significantly greater than by sugar maple compared with the contribution of each species to the canopy composition. This greater ice damage to beech suggests that reciprocal replacement processes involving beech and maple seedlings cannot completely account for the maintenance of beech–maple codominance in northern forests subject to relatively frequent ice storms. We hypothesize that the ability of beech to root sprout is important in compensating for its greater susceptibility to ice damage and contributes to the maintenance of beech–maple codominance in northern forests.

Increased plasma catecholamines in patients with Friedreich's ataxia

We studied free plasma catecholamines in 23 patients with Friedreich's ataxia, having a mean age of 22 +/- 9.6 (SD) years. Conjugated catecholamines were also studied in 10 patients. Mean plasma norepinephrine and epinephrine were significantly higher than controls both in the supine and standing positions. In total 15 out of 23 patients (65%) had increase free and/or conjugated plasma catecholamines. The increased in plasma catecholamines was more marked in patients with severe neuromotor impairment. Among the patients with left ventricular concentric hypertrophy (wall thickness greater than 12 mm), only 3 had no demonstrable sympathetic hyperfunction. Since the high local concentrations of norepinephrine at the site of release from sympathetic nerve terminals may serve as a trigger for the hypertrophic response of the myocardial cell, it is suggested that early pharmacological intervention could prevent or limit the cardiomyopathic process or its clinical consequences.

Taurine in cerebrospinal fluid in Friedreich's ataxia

In a previous study we reported low values of taurine and aspartic acid in the CSF of patients with Friedreich's ataxia, when the results were compared to the literature. Further studies have revealed that unforetold difficulties with the advertised methodology of sequential multi-sample amino acid analysis were responsible for low values in the determination of these two amino acids in the small volumes necessary for CSF. A corrected method is presented. With the latter method the differences disappear for CSF taurine and aspartic acid, but they remain valid for the previously reported blood and urine values in Friedreich's ataxia. GABA levels are also normal in Friedreich's ataxia CSF.

Glucose and insulin metabolism in Friedreich's ataxia

Our prospective survey of 50 ataxic patients confirms the previous finding of frequent clinical or chemical diabetes in Friedreich's ataxia. Eighteen percent of our typical cases have clinical diabetes and 40% at least an abnormal glucose tolerance curve. However, this finding does not appear to be specific to that form of ataxia. Furthermore, we have shown that most patients with ataxia have normal or low fasting insulin levels, but a hyperinsulinic response to a glucose load.