Sensorineural Hearing Loss in a Child with Succinic Semialdehyde Dehydrogenase Deficiency.

Succinic semialdehyde dehydrogenase (SSADH) deficiency is a rare autosomal-recessive disorder of gamma-aminobutyric acid (GABA) metabolism, resulting in accumulation of GABA and gamma-hydroxybutyric acid (GHB) in physiological fluids. Approximately 450 patients have been diagnosed worldwide with this inherited neurotransmitter disorder. We report on a five-year-old male patient, homozygous for the pathogenic variant (NM_170740:c.1265G>A) in ALDH5A1 presenting with an unexpected association of typical SSADH deficiency manifestations with bilateral sensorineural hearing loss (SNHL). Brainstem evoked response audiometry (BERA) testing showed mid-frequency sensorineural hearing damage that suggested a hereditary component to SNHL. Whole exome sequencing (WES) failed to discern other genetic causes of deafness. Several variants of uncertain significance (VUS) detected in genes known for their role in hearing physiology could not be verified as the cause for the SNHL. It is known that central auditory processing depends on a delicate balance between excitatory and inhibitory neurotransmission, and GABA is known to play a significant role in this process. Additionally, excessive concentrations of accumulated GABA and GBH are known to cause a down-regulation of GABA receptors, which could have an adverse influence on hearing function. However, these mechanisms are very speculative in context of SNHL in a patient with inherited disorder of GABA metabolism. Injury of the globi pallidi, one of hallmarks of SSADH deficiency, could also be a contributory factor to SNHL, as was suspected in some other inborn errors in metabolism. We hope that this case will contribute to the understanding of phenotypic complexity of SSADH deficiency.

Expanding the Phenotypic Spectrum: Chronic Kidney Disease in a Patient with Combined Oxidative Phosphorylation Defect 21.

Introduction: Pathogenic variants in TARS2 are associated with combined oxidative phosphorylation deficiency 21 (COXPD21), an autosomal recessive disorder usually presenting as mitochondrial encephalomyopathy. Kidney impairment has been documented in a minority of COXPD21 patients, mostly with distal renal tubular acidosis. Case report: We report on the first COXPD21 patient with generalized tubular dysfunction and early childhood progression to chronic kidney disease (CKD). Thorough diagnostic evaluation was initiated at six months of age due to failure to thrive, muscular hypotonia, motor delay and recurrent bronchiolitis. The boy was lost to follow-up until the age of two years, when he was readmitted with elevated creatinine level, reduced estimated glomerular filtrate rate, normochromic anaemia, metabolic acidosis and hyperkalaemia. Urine abnormalities pointed to generalized tubular dysfunction. Two novel heterozygous missense variants in TARS2 gene were detected by the means of whole exome sequencing: c.1298T>G (p.Phe438Cys) of maternal origin and c.1931A>T (p.Asp644Val) of paternal origin. Currently, at 4.5 years of age, the boy has failure to thrive, severe motor and verbal delay and end stage of CKD. We referred the patient to paediatric centre that provides renal replacement therapy. Conclusion: The overall clinical course in the patient we report on corresponds well to the previously reported cases of TARS2 related COXPD21, especially in regard to neurological and developmental aspects of the disease. However, we point out the generalized tubulopathy and early occurrence of CKD in our patient as atypical renal involvement in COXPD21. Additionally, this is the first report of hypothyroidism and hypoparathyroidism in a COXPD21 patient.

A Novel Variant in the LIPA Gene Associated with Distinct Phenotype.

Deficiency of lysosomal acid lipase (LAL-D) is caused by biallelic pathogenic variants in the LIPA gene. Spectrum of LAL-D ranges from early onset of hepatosplenomegaly and psychomotor regression (Wolman disease) to a more chronic course (cholesteryl ester storage disease - CESD). The diagnosis is based on lipid and biomarker profiles, specific liver histopathology, enzyme deficiency, and identification of causative genetic variants. Biomarker findings are a useful for diagnostics of LAL-D, including high plasma concentration of chitotriosidase as well as elevated oxysterols. Current treatment options include enzyme replacement therapy (sebelipase-alpha), statins, liver transplantation, and stem cell transplantation. We present two pairs of siblings from Serbia with a distinctive phenotype resembling LAL-D with a novel variant of unknown significance (VUS) detected in the LIPA gene and residual LAL activity. All patients presented with hepatosplenomegaly at early childhood. In siblings from family 1, compound heterozygosity for a pathogenic c.419G>A (p.Trp140Ter) variant and a novel VUS c.851C>T (p.Ser284Phe) was detected. Patients from family 2 were homozygous for c.851C>T VUS and both have typical histopathologic findings for LAL-D in the liver. Enzyme activity of LAL was tested in three patients and reported as sufficient, and therefore enzyme replacement therapy could not be approved. When confronted with a challenge of diagnosing an inherited metabolic disorder, several aspects are taken into consideration: clinical manifestations, specific biomarkers, enzyme assay results, and molecular genetic findings. This report brings cases to light which have a considerable discrepancy between those aspects, namely the preserved LAL enzyme activity in presence of clinical manifestations and rare variants in the LIPA gene.

Ambiguous Genitalia and Lissencephaly in A 46,XY Neonate with a Novel Variant of Aristaless Gene.

Introduction: Disorders of sexual development can present isolated or as a part of complex genetic syndromes. Case presentation: A newborn with ambiguous genitalia and prenatally diagnosed brain malformations was referred to our hospital. Prenatal ultrasound examination and MRI showed lissencephaly and absence of the corpus callosum. At admission, physical examination revealed microphallus, hypospadia and complete fusion of labioscrotal folds with nonpalpable gonads, normal blood pressure and serum biochemistry. Cortisol level was normal (201 nmol/L), testosterone elevated (14.4 nmol/L), FSH 0.1 IU/L, LH 0.7 IU/L, estradiol 241 pmol/L. Seizures were noted on the 2nd day and the child was started on anticonvulsives. When 17-OHP level results came back elevated (200 nmol/L), ACTH test was performed and the child was started on hydrocortisone and fludrocortisone treatment. Congenital adrenal hyperplasia became unlikely when karyotype result showed normal male karyotype (46, XY, SRY+) with no Mullerian structures seen on ultrasonographic exam. As association of ambiguous genitalia and lissencephaly strongly suggested a mutual genetic background, diagnosis of X-linked lissencephaly with ambiguous genitalia (X-LAG) became apparent. Conclusions: The presented case highlights the importance of looking at the whole clinical picture instead of separate isolated findings with emphasis on patient-centered approach guided by clinical findings and patient history.

Genetic characterization of GSD I in Serbian population revealed unexpectedly high incidence of GSD Ib and 3 novel SLC37A4 variants.

Glycogen storage disease (GSD) type I is inborn metabolic disease characterized by accumulation of glycogen in multiple organs. We analyzed 38 patients with clinical suspicion of GSD I using Sanger and next-generation sequencing (NGS). We identified 28 GSD Ib and 5 GSD Ia patients. In 5 patients, GSD III, VI, IX, cholesteryl-ester storage disease and Shwachman-Diamond syndrome diagnoses were set using NGS. Incidences for GSD Ia and GSD Ib were estimated at 1:172 746 and 1:60 461 live-births, respectively. Two variants were identified in G6PC gene: c.247C>T (p.Arg83Cys) and c.518T>C (p.Leu173Pro). In SLC37A4 gene, 6 variants were detected. Three previously reported variants c.81T>A (p.Asn27Lys), c.162C>A (p.Ser54Arg) and c.1042_1043delCT (p.Leu348Valfs*53) accounted for 87% of all analyzed alleles. Computational, transcription studies and/or clinical presentation in patients confirmed pathogenic effect of 3 novel variants: c.248G>A (p.Gly83Glu), c.404G>A (p.Gly135Asp) and c.785G>A (p.Ser263Glyfs*33 or p.Gly262Asp). In the cohort, hepatomegaly, hypoglycemia and failure to thrive were the most frequent presenting signs of GSD Ia, while hepatomegaly and recurrent bacterial infections were clinical hallmarks of GSD Ib. All GSD Ib patients developed neutropenia while 20.6% developed inflammatory bowel disease. Our study revealed the highest worldwide incidence of GSD Ib. Furthermore, description of 3 novel variants will facilitate medical genetic practice.

Genotype-phenotype correlation in 44 Czech, Slovak, Croatian and Serbian patients with mucopolysaccharidosis type II.

Mucopolysaccharidosis type II (Hunter syndrome, MPS II, OMIM 309900) is an X-linked lysosomal storage disorder caused by deficiency of iduronate-2-sulfatase (IDS). We analyzed clinical and laboratory data from 44 Slavic patients with this disease. In total, 21 Czech, 7 Slovak, 9 Croatian and 7 Serbian patients (43 M/1 F) were included in the study (median age 11.0 years, range 1.2-43 years). Birth prevalence ranged from 1:69,223 (Serbia) to 1:192,626 (Czech Rep.). In the majority of patients (71%), the disease manifested in infancy. Cognitive functions were normal in 10 patients. Four, six and 24 patients had mild, moderate, and severe developmental delay, respectively, typically subsequent to developmental regression (59%). Residual enzyme activity showed no predictive value, and estimation of glycosaminoglycans (GAGs) had only limited importance for prognosis. Mutation analysis performed in 36 families led to the identification of 12 novel mutations, eight of which were small deletions/insertions. Large deletions/rearrangements and all but one small deletion/insertion led to a severe phenotype. This genotype-phenotype correlation was also identified in six cases with recurrent missense mutations. Based on patient genotype, the severity of the disease may be predicted with high probability in approximately half of MPS II patients.

Molecular and phenotypic characteristics of seven novel mutations causing branched-chain organic acidurias.

Specific mitochondrial enzymatic deficiencies in the catabolism of branched-chain amino acids cause methylmalonic aciduria (MMA), propionic acidemia (PA) and maple syrup urine disease (MSUD). Disease-causing mutations were identified in nine unrelated branched-chain organic acidurias (BCOA) patients. We detected eight previously described mutations: p.Asn219Tyr, p.Arg369His p.Val553Glyfs*17 in MUT, p.Thr198Serfs*6 in MMAA, p.Ile144_Leu181del in PCCB, p.Gly288Valfs*11, p.Tyr438Asn in BCKDHA and p.Ala137Val in BCKDHB gene. Interestingly, we identified seven novel genetic variants: p.Leu549Pro, p.Glu564*, p.Leu641Pro in MUT, p.Tyr206Cys in PCCB, p.His194Arg, p.Val298Met in BCKDHA and p.Glu286_Met290del in BCKDHB gene. In silico and/or eukaryotic expression studies confirmed pathogenic effect of all novel genetic variants. Aberrant enzymes p.Leu549Pro MUT, p.Leu641Pro MUT and p.Tyr206Cys PCCB did not show residual activity in activity assays. In addition, activity of MUT enzymes was not rescued in the presence of vitamin B12 precursor in vitro which was in accordance with non-responsiveness or partial responsiveness of patients to vitamin B12 therapy. Our study brings the first molecular genetic data and detailed phenotypic characteristics for MMA, PA and MSUD patients for Serbia and the whole South-Eastern European region. Therefore, our study contributes to the better understanding of molecular landscape of BCOA in Europe and to general knowledge on genotype-phenotype correlation for these rare diseases.