Dariusz Rokicki

Elevated Carbohydrate-Deficient Transferrin (CDT) and Its Normalization on Dietary Treatment as a Useful Biochemical Test for Hereditary Fructose Intolerance and Galactosemia

Abnormalities in protein glycosylation are reported in fructosemia (HFI) and galactosemia, although, particularly in HFI, the published data are limited to single cases. The purpose was to investigate the usefulness of the carbohydrate-deficient transferrin (CDT) profile for identification and monitoring of these disorders. First we analyzed CDT values before and shortly after the diagnosis in 10 cases of HFI and 17 cases of galactosemia. In all patients, elevated CDT levels were found that significantly (p < 0.0001) decreased with the therapeutic diet (27.3 ± 11.5% versus 9.3 ± 5.1% for HFI and 43.8 ± 14.1% versus 11.2 ± 4.0% for galactosemia). To evaluate the use of CDT test in monitoring compliance, the test was performed in 25 HFI patients on fructose-restricted diet. We found an elevated CDT level on 104 from 134 tests (mean 11.3 ± 5.5%, control 1.5%–6.2%). The fructose intake was found to be 90 ± 70 mg/kg/d, and the diet was unbalanced. A number of patients presented lower height, elevated urinary uric acid excretion, and hypercalciuria. In conclusion, abnormal percentage of CDT (%CDT) values may allow prompt detection of HFI (or galactosemia). Persistence of some abnormalities in HFI on treatment may be caused by trace amounts of fructose ingestion and/or a deficient diet. Regular %CDT measurements are suggested for HFI treatment monitoring.

Congenital disorder of glycosylphosphatidylinositol (GPI)-anchor biosynthesis—The phenotype of two patients with novel mutations in the PIGN and PGAP2 genes

BACKGROUND Glycosylphosphatidylinositol (GPI)-anchor deficiencies are a new subclass of congenital disorders of glycosylation. About 26 genes are involved in the GPI-anchor biosynthesis and remodeling pathway, of which mutations in thirteen have been reported to date as causative of a diverse spectrum of intellectual disabilities. Since the clinical phenotype of these disorders varies and the number of described individuals is limited, we present new patients with inherited GPI-anchor deficiency (IGD) caused by mutations in the PGAP2 and PIGN genes. PATIENTS AND METHODS The first girl presented with profound psychomotor retardation, low birth parameters, and chest deformities already existing in neonatal period. The disease course was slowly progressive with severe hypotonia, chronic fever, and respiration insufficiency at the age of 6. The second girl showed profound psychomotor retardation, marked hypotonia, and high birth weight (97 centile). Dysmorphy was mild or absent in both girls. Whole exome sequencing revealed novel variants in the genes PGAP2 (c.2T>G and c.221G>A) and PIGN (c.790G>A and c.932T>G). Impaired GPI binding were was subsequently uncovered, although the hyperactivity of alkaline phosphatase (a GPI-anchored protein) occurred only in first case. CONCLUSIONS Based on our results we can conclude that: 1. GPI-anchor biosynthesis disorders may represent a relatively frequent and overlooked metabolic defect; 2. The utility of GPI binding assessment as a screening test for this group of rare diseases requires further studies.

NAXE Mutations Disrupt the Cellular NAD(P)HX Repair System and Cause a Lethal Neurometabolic Disorder of Early Childhood

To safeguard the cell from the accumulation of potentially harmful metabolic intermediates, specific repair mechanisms have evolved. APOA1BP, now renamed NAXE, encodes an epimerase essential in the cellular metabolite repair for NADHX and NADPHX. The enzyme catalyzes the epimerization of NAD(P)HX, thereby avoiding the accumulation of toxic metabolites. The clinical importance of the NAD(P)HX repair system has been unknown. Exome sequencing revealed pathogenic biallelic mutations in NAXE in children from four families with (sub-) acute-onset ataxia, cerebellar edema, spinal myelopathy, and skin lesions. Lactate was elevated in cerebrospinal fluid of all affected individuals. Disease onset was during the second year of life and clinical signs as well as episodes of deterioration were triggered by febrile infections. Disease course was rapidly progressive, leading to coma, global brain atrophy, and finally to death in all affected individuals. NAXE levels were undetectable in fibroblasts from affected individuals of two families. In these fibroblasts we measured highly elevated concentrations of the toxic metabolite cyclic-NADHX, confirming a deficiency of the mitochondrial NAD(P)HX repair system. Finally, NAD or nicotinic acid (vitamin B3) supplementation might have therapeutic implications for this fatal disorder.

Biallelic Mutations in TMEM126B Cause Severe Complex I Deficiency with a Variable Clinical Phenotype

Complex I deficiency is the most common biochemical phenotype observed in individuals with mitochondrial disease. With 44 structural subunits and over 10 assembly factors, it is unsurprising that complex I deficiency is associated with clinical and genetic heterogeneity. Massively parallel sequencing (MPS) technologies including custom, targeted gene panels or unbiased whole-exome sequencing (WES) are hugely powerful in identifying the underlying genetic defect in a clinical diagnostic setting, yet many individuals remain without a genetic diagnosis. These individuals might harbor mutations in poorly understood or uncharacterized genes, and their diagnosis relies upon characterization of these orphan genes. Complexome profiling recently identified TMEM126B as a component of the mitochondrial complex I assembly complex alongside proteins ACAD9, ECSIT, NDUFAF1, and TIMMDC1. Here, we describe the clinical, biochemical, and molecular findings in six cases of mitochondrial disease from four unrelated families affected by biallelic (c.635G>T [p.Gly212Val] and/or c.401delA [p.Asn134Ilefs∗2]) TMEM126B variants. We provide functional evidence to support the pathogenicity of these TMEM126B variants, including evidence of founder effects for both variants, and establish defects within this gene as a cause of complex I deficiency in association with either pure myopathy in adulthood or, in one individual, a severe multisystem presentation (chronic renal failure and cardiomyopathy) in infancy. Functional experimentation including viral rescue and complexome profiling of subject cell lines has confirmed TMEM126B as the tenth complex I assembly factor associated with human disease and validates the importance of both genome-wide sequencing and proteomic approaches in characterizing disease-associated genes whose physiological roles have been previously undetermined.

Biallelic mutations in CYP24A1 or SLC34A1 as a cause of infantile idiopathic hypercalcemia (IIH) with vitamin D hypersensitivity: molecular study of 11 historical IIH cases

Idiopathic infantile hypercalcemia (IIH) is a mineral metabolism disorder characterized by severe hypercalcemia, failure to thrive, vomiting, dehydration, and nephrocalcinosis. The periodical increase in incidence of IIH, which occurred in the twentieth century in the United Kingdom, Poland, and West Germany, turned out to be a side effect of rickets over-prophylaxis. It was recently discovered that the condition is linked to two genes, CYP24A1 and SLC34A1. The aim of the study was to search for pathogenic variants of the genes in adult persons who were shortlisted in infancy as IIH caused by “hypersensitivity to vit. D”. All persons were found to carry mutations in CYP24A1 or SLC34A1, nine and two persons respectively. The changes were biallelic, with one exception. Incidence of IIH in Polish population estimated on the basis of allele frequency of recurrent p.R396W CYP24A1 variant, is 1:32,465 births. It indicates that at least a thousand homozygotes and compound heterozygotes with risk of IIH live in the country. Differences in mechanism of developing hypercalcemia indicate that its prevention may vary in both IIH defects. Theoretically, vit. D restriction is a first indication for CYP24A1 defect (which disturbs 1,25(OH)2D degradation) and phosphate supplementation for SLC34A1 defect (which impairs renal phosphate transport). In conclusion, we suggest that molecular testing for CYP24A1 and SLC34A1 mutations should be performed in each case of idiopathic hypercalcemia/hypercalciuria, both in children and adults, to determine the proper way for acute treatment and complications prevention.

Difficulties in recognition of pyruvate dehydrogenase complex deficiency on the basis of clinical and biochemical features. The role of next-generation sequencing.

Pyruvate dehydrogenase complex (PDHc) defect is a well-known cause of mitochondrial disorders (MD) with at least six responsible genes (PDHA1, PDHB, DLAT, DLD, PDHX, PDP1). The aim of this work was to assess the diagnostic value of biochemical methods in recognition of PDHc defect in Polish patients with suspicion of MD. In the first step, Western blot of the E1α subunit was performed on 86 archive muscle bioptates with suspicion of MD. In the second step, Sanger PDHA1 sequencing was performed in 21 cases with low E1α expression. In the third step, 7 patients with negative results of PDHA1 sequencing were subjected to whole-exome sequencing (WES). This protocol revealed 4 patients with PDHA1 and one with DLD mutations. Four additional probands were diagnosed outside the protocol (WES or Sanger sequencing). The molecular characterization of PDHc defect was conducted in a total of 9 probands: 5 according to and 4 off the protocol. Additionally, two affected relatives were recognized by a family study. Altogether we identified seven different PDHA1 changes, including two novel variants [c.464T > C (p.Met155Thr) and c.856_859dupACTT (p.Arg288Leufs*10)] and one DLD variant. The lactate response to glucose load in the PDHA1 subset was compared to a subset of non PDHc-related MD. Opposite responses were observed, with an increase of 23% and decrease of 27%, respectively. The results show that determining lactate response to glucose load and muscle E1α expression may contribute to distinguishing PDHc-related and other MD, however, WES is becoming the method of choice for MD diagnostics.

Neurologic Presentation, Diagnostics, and Therapeutic Insights in a Severe Case of Adenylosuccinate Lyase Deficiency:

Epilepsy in adenylosuccinate lyase deficiency may be difficult to treat, and there is no standardized therapy. The authors describe a case of severe adenylosuccinate lyase deficiency resulting from a heterozygous mutation of the ADSL gene (p.D215H/p.I351T). The patient presented with tonic-clonic seizures, opisthotonus, tremor, and myoclonus in the 4th day of life. The seizures were refractory on various combinations of antiepileptic treatment. A ketogenic diet was introduced at the age of 2 resulting in a seizure-free period. The patient, however, developed a metabolic hyperchloremic acidosis with Fanconi syndrome, which disappeared a month after cessation of the diet at the age of 5. Since the withdrawal of the ketogenic diet, seizures have returned to a frequency of several times a day. In conclusion, a ketogenic diet could be considered a valid therapeutic option in patients with intractable seizures in a course of adenylosuccinate lyase deficiency; however, it requires a formal study.

Bilateral striatal necrosis caused by ADAR mutations in two siblings with dystonia and freckles-like skin changes that should be differentiated from Leigh syndrome

Pathogenic molecular variants in the ADAR gene are a known cause of rare diseases, autosomal recessive Aicardi- Goutières syndrome type 6, severe infantile encephalopathy with intracranial calcifications and dominant dyschromatosis symmetrica hereditaria, demonstrated mainly in Asian adults. Recently, they have been also found in patients with nonsyndromic bilateral striatal necrosis accompanied by skin changes of the freckles-like type. Here, we present Polish siblings with acute onset and slowly progressive extrapyramidal syndrome with preserved intellectual abilities and basal ganglia changes found in MRI. A Leigh syndrome was considered for a long time as the most frequent cause of such lesions in children. Finally, two molecular variants in non-mitochondria-related ADAR gene c.3202+1G>A (p.?) and c.577C>G (p.Pro193Ala) were revealed by whole exome sequencing. We suggest that bilateral striatal necrosis should be always differentiated from LS to prevent the diagnosis delay. The striatal involvement accompanied by the presence of freckles-like skin changes should direct differential diagnosis to the ADAR gene mutations screening.

Tyrosinemia type III in an asymptomatic girl

Tyrosinemia type 3 (HT3) is a rare inborn error of tyrosine metabolism caused by mutations in the HPD gene encoding 4-hydroxyphenyl-pyruvate dioxygenase, which is transmitted in an autosomal recessive trait. The disorder is characterized by tyrosine accumulation in body fluids and massive excretion of tyrosine derivatives into urine (www.orpha.net). Since it is the least frequent form of tyrosinemia, only few cases with the variable but rather mild clinical features have been described so far. We report an 11 year old girl presenting with no clinical symptoms and with normal mental development who has been diagnosed with HT3 through metabolic screening on the basis of elevated serum level of tyrosine ranging from 425 to 535 μmol/L (normal values: 29–86 μmol/L), and elevated urinary excretion of p-hydroxyphenyl derivatives confirmed genetically with the homozygous c.479A > G (p.Tyr160Cys) missense change in the HPD gene. The girl has been only presenting with recurrent proteinuria of unknown etiology. A phenylalanine- and tyrosine-restricted diet has never been administered. Presented case may suggest that high tyrosine concentration itself does not participate directly in neuronal damage described in patients with tyrosinemia type 3.

Pediatric patient with hyperketotic hypoglycemia diagnosed with glycogen synthase deficiency due to the novel homozygous mutation in GYS2.

Background Glycogen synthase deficiency (glycogen storage disease 0 — GSD 0) caused by mutations in the GYS2 gene is characterized by a lack of glycogen synthesis in the liver. It is a rare condition of disturbed glycogen homeostasis in the liver with less than 30 cases reported in the literature so far. Case report We report a 9 year old boy diagnosed with GSD 0 due to the newly identified, highly pathogenic homozygous mutation: NM_021957.3:p.Phe574Leu/c.1720T > C in ex. 14. A random, asymptomatic hypoglycemia with ketonuria was found in this patient at the age of 7. His developmental parameters were within normal ranges. Oral glucose tolerance test showed normal baseline blood levels of glucose, insulin and lactate, and their increase following glucose intake. Eight-hour fasting plasma glucose test, revealed glucose blood level of 34 mg/dl with no clinical symptoms. The results of these tests suggested GSD 0. Molecular analysis of the GYS2 gene was not feasible, but this particular gene was included in the panel of hypoglycemia of whole exome sequencing (WES) which was at our disposal.