The Clinical and Molecular Characteristics of Molybdenum Cofactor Deficiency Due to MOCS2 Mutations

BACKGROUND

We explored the clinical and molecular characteristics of molybdenum cofactor deficiency due to MOCS2 muations.

METHODS

We summarize the genetic and clinical findings of previously reported patients with a MOCS2 mutation. We also present a new patient with novel neuroradiological findings associated with molybdenum cofactor deficiency due to a novel homozygous variant in the 5' untranslated region of the MOCS2 gene.

RESULTS

The study population comprised 35 patients with a MOCS2 gene mutation. All reported children had delayed motor milestones. The major initial symptom was seizures in neonatal period. Facial dysmorphism was present in 61% of the patients. Only one patient had ectopia lentis. Agenesis of the corpus callosum and an associated interhemispheric cyst in our case are novel neuroradiological findings.

CONCLUSIONS

The occurrence of neonatal seizures and feeding difficulties can be the first clinical signs of molybdenum cofactor deficiency. Although there is no effective therapy for this condition, early diagnosis and genetic analysis of these lethal disorders facilitate adequate genetic counseling.

Role of excessive maternal iron in the pathogenesis of congenital leukoencephalomalacia in captive black rhinoceroses (Diceros bicornis)

OBJECTIVE

To investigate the possibility that excessive maternal iron (overload) may contribute to development of congenital leukoencephalomalacia in captive black rhinoceroses.

SAMPLE POPULATION

Tissue specimens and serum samples from 18 rhinoceroses in 2 kindreds harboring 4 (possibly 5) affected female calves.

PROCEDURE

Fresh and archival sera and necropsy tissue specimens were evaluated to determine the nature and extent of iron overload in captive and wild black rhinoceroses as well as other rhinoceros species.

RESULTS

Quantitative serum and tissue assays of iron and iron analytes, corroborated by histopathologic findings, indicated that these kindreds carried the greatest body burdens of iron yet found among captive black rhinoceroses. Fourteen of 18 rhinoceroses had the highest serum ferritin concentrations measured among 64 black rhinoceroses in captivity in the United States. Dams of affected calves had serum ferritin concentrations 2 orders of magnitude higher than clinically normal humans, equids, or free-ranging rhinoceroses. A neonatal serum sample from 1 affected female calf had a high ferritin concentration (approx 100-fold increase), but a male sibling of another affected female did not, suggesting a possible sex disparity in fetal response to maternal iron overload. Morphologic hallmarks of hemochromatosis were prominent in dams and grandams of affected calves.

CONCLUSIONS AND CLINICAL RELEVANCE

Excessive maternal iron may affect female fetuses more than males, possibly inducing leukoencephalomalacia by catalyzing production of highly toxic hydroxyl free radicals during crucial periods of in utero development. Reduction of maternal iron overload may decrease the probability of developing leukoencephalomalacia and some other disorders commonly affecting rhinoceroses in captivity.

[Multicystic encephalomalacia in twin pregnancies]

Multicystic encephalomalacia (ME) is a rare entity in the pediatric age. In ME brain tissue in substituted by cavities of variable size. ME has different etiologies being asphyxia and circulatory alterations the most important factors. In monozygotic twins there is an increased incidence of structural anomalies than dizygotic twins. We present four twin patients with ME. Three of them had a prenatal dead sibling. The fourth pair of twins had a twin-twin transfusion. We want to stress the utility of brain echography in early diagnosis of ME.

X-linked Leigh's syndrome

Two male half siblings developed rapid progression of neurologic symptoms at 11/2 and 21/2 years of age. Neither boy had a metabolic acidosis. Characteristic features of subacute necrotizing encephalomyelopathy, the neuropathologic basis of Leigh's syndrome, were demonstrated at autopsy. X-linkage of the disorder was considered because the boys had different fathers. An X-linked form of Leigh's syndrome was supported by a review of the literature, which showed an unexplained male/female ratio in Leigh's syndrome of 1.83/1, and a significant excess of male-male siblings. An X-linked form of Leigh's syndrome would explain the excess of males, and may account for some of the clinical and biochemical heterogeneity.

Erythrocyte transketolase activity in suspected cases of Leigh's disease, or subacute necrotising encephalomyelopathy

Erythrocyte transketolase activity and the effect of adding thiamine pyrophosphate (% thiamine pyrophosphate effect) were measured in 111 subjects suspected to suffer from Leigh's disease (subacute necrotising encephalomyelopathy). From clinical evidence these subjects were divided into five groups: (1) necropsy-proved cases of subacute necrotising encephalomyelopathy, (2) cases positive for urinary thiamine pyrophosphate: adenosine triphosphate phosphotransferase inhibitor, (3) clinically likely cases of subacute necrotising encephalomyelopathy (patients still alive, or on whom no necropsy was performed), (4) cases diagnosed as diseases other than subacute necrotising encephalomyelopathy (control group), (5) cases for which no diagnosis had been made. Comparison of erythrocyte transketolase activities with and without added thiamine pyrophosphate and of the % thiamine pyrophosphate effect for each group compared with the control group showed no statistically significant differences from normal values for any of these parameters. Similarly, there were no differences between the two sexes in transketolase activity, and no correlation between transketolase activity and age. These results indicate that erythrocyte transketolase activity is not altered in subacute necrotising encephalomyelopathy and is unlikely to be of value for the diagnosis of Leigh's disease.

Chronic Leigh Disease: a genetic and biochemical study

The large family of a 21-year-old man who died of Leigh disease was investigated for evidence of neurological abnormalities and presence of the adenosine triphosphate-thiamine diphosphate phosphoryltransferase inhibitor factor. Of 217 persons (seven generations) included in the pedigree, 68 were examined neurologically and biochemically. Fourteen (20%), 5 of whom had abnormal neurological findings, were found to excrete the inhibitor factor. Clinical manifestations varied from severe neurological affliction to subtle deficits. A chronic relapsing course was frequently encountered, with exacerbations occurring in association with apparent metabolic stress. Parental consanguinity was identified in the propositus as well as in other family members with neurological abnormalities. Males and females were affected, and no vertical transmission of the trait was found. These multigenerational data suggest that Leigh disease in adults is inherited in an autosomal recessive manner and has variable degrees of expression with a wide spectrum of neurological manifestations.

[Subacute necrotizing encephalomielopathy. Leigh syndrome (author's transl)]

A 6-month-old girl with familiar history of two dead sisters few months old, was admitted to the Hospital with a neurological process. After her admission progressively worsened until her death. The patient had clinical manifestation of proximal tubular acidosis. Levels of lactic and piruvic acid were normal. Necropsic study was compatible with the diagnoses of subacute necrotizing encephalomielopathy of Leigh syndrome.

[Subacute necrotizing encephalomyelopathy (Leigh's disease) (author's transl)]

The characteristic neuropathological features of subacute necrotizing encephalomyelopathy (Leigh), their histology and distribution are described. Clinical findings are unspecific. Impairment of feeding. vomitus, respiratory abnormality, retardation of psychomotor development, familial incidence and onset in early childhood are prominent symptoms. Atactic and athetoid movements, optic atrophy, oculomotor abnormalities are observed in most cases. An enzyme inhibitor excreted in the urine seems to be related to an inborn error of thiamine dependent metabolism in brain tissue. Treatment with thiamine derivatives may have a beneficial effect on the clinical course.