Decreased calcium permeability caused by biallelic TRPV5 mutation leads to autosomal recessive renal calcium-wasting hypercalciuria.

Hypercalciuria is the most common metabolic risk factor in people with kidney stone disease. Its etiology is mostly multifactorial, although monogenetic causes of hypercalciuria have also been described. Despite the increased availability of genetic diagnostic tests, the vast majority of individuals with familial hypercalciuria remain unsolved. In this study, we investigated a consanguineous pedigree with idiopathic hypercalciuria. The proband additionally exhibited severe skeletal deformities and hyperparathyroidism. Whole-exome sequencing of the proband revealed a homozygous ultra-rare variant in TRPV5 (NM_019841.7:c.1792G>A; p.(Val598Met)), which encodes for a renal Ca2+-selective ion channel. The variant segregates with the three individuals with hypercalciuria. The skeletal phenotype unique to the proband was due to an additional pathogenic somatic mutation in GNAS (NM_000516.7:c.601C>T; p.(Arg201Cys)), which leads to polyostotic fibrous dysplasia. The variant in TRPV5 is located in the TRP helix, a characteristic amphipathic helix that is indispensable for the gating movements of TRP channels. Biochemical characterization of the TRPV5 p.(Val598Met) channel revealed a complete loss of Ca2+ transport capability. This defect is caused by reduced expression of the mutant channel, due to misfolding and preferential targeting to the proteasome for degradation. Based on these findings, we conclude that biallelic loss of TRPV5 function causes a novel form of monogenic autosomal recessive hypercalciuria, which we name renal Ca2+-wasting hypercalciuria (RCWH). The recessive inheritance pattern explains the rarity of RCWH and underscores the potential prevalence of RCWH in highly consanguineous populations, emphasizing the importance of exploration of this disorder within such communities.

Mutated Transcripts of ZEB2 Do Not Undergo Nonsense-Mediated Decay in Mowat-Wilson Syndrome.

Introduction: Mowat-Wilson syndrome (MWS) is an autosomal-dominant complex developmental disorder characterized by distinctive facial appearance, intellectual disability, epilepsy, and various clinically heterogeneous abnormalities reminiscent of neurocristopathies. MWS is caused by haploinsufficiency of ZEB2 due to heterozygous point mutations and copy number variations. Case Presentation: We report on two unrelated affected individuals with novel ZEB2indel mutations, molecularly confirming the diagnosis of MWS. Quantitative real-time polymerase chain reaction (PCR) for the comparison of total transcript levels and allele-specific quantitative real-time PCR were also performed and demonstrated that the truncating mutations did not lead to nonsense-mediated decay as expected. Conclusion: ZEB2 encodes a multifunctional pleiotropic protein. Novel mutations in ZEB2 should be reported in order that genotype-phenotype correlations might be established in this clinically heterogeneous syndrome. Further cDNA and protein studies may help elucidate the underlying pathogenetic mechanisms of MWS since nonsense-mediated RNA decay was found to be absent in only a few studies including this study.

Hemolytic Anemia due to Glucose 6 Phosphate Dehydrogenase Deficiency Triggered by Type 1 Diabetes Mellitus

Glucose 6 phosphate dehydrogenase (G6PD) is expressed in all tissues and is necessary to maintain oxidant stress capacity of cells. G6PD deficiency is the most common enzymopathy in humans and is among the important causes of hemolytic anemia. It has been reported that severe hemolytic anemia due to G6PD deficiency may develop in newly diagnosed diabetes, especially during the correction of hyperglycemia. To date, nine cases have been published. Genetic analysis was not performed for G6PD deficiency in these published patients. We present a case of hemolytic anemia due to G6PD deficiency secondary to newly diagnosed type 1 diabetes mellitus. Genetic testing was performed for the index patient and revealed a previously reported missense pathogenic variant (c.653C>T; p.Ser218Phe) in the G6PD gene.

Novel Cranial Imaging Findings and a Splice-Site Variant in a Patient with Tyrosinemia Type III, and a Summary of Published Cases.

Tyrosinemia type III is an extremely rare autosomal recessive disease, with only 19 patients yet reported. It is caused by a deficiency of the 4-hydroxyphenylpyruvate dioxygenase enzyme, resulting from biallelic mutations in the HPD gene. Although the clinical spectrum of the disease is not fully known, most patients present with neurodevelopmental symptoms. We report on a 20-month-old patient who was investigated due to developmental delay and dysmorphic features. The girl had a novel splice-site mutation in the HPD gene and ventriculomegaly in cranial imaging, which was not previously associated with tyrosinemia type III. Our patient had mild subjective improvement in social skills and language development after dietary therapy was started and her tyrosine levels decreased. We also summarize clinical, biochemical, and genetic findings of previously published patients with biallelic HPD mutations.

Mild phenotype in two siblings with a missense GHR variant.

OBJECTIVES:  Laron syndrome (LS) is a disease caused by growth hormone receptor (GHR) defects. It is characterized by severe postnatal growth retardation and distinctive facial features. CASE PRESENTATION: In this case report, we describe the clinical and biochemical characteristics of two siblings with LS, a sister and a brother, and identify a homozygous c.344A> C (p.Asn115Thr) variant in GHR. The sister was 11 years 9 months old with a height of 127.5 cm (-3.86 SDS), and the brother was 14 years 10 months old with a height of 139 cm (-4.27 SDS). Their phenotype did not have features suggesting classical LS. CONCLUSION: In the current literature, there are three cases with the same missense variant. Our cases differ from them in clinical (higher height SDS, mild dysmorphism including a broad forehead, malar hypoplasia, prominent columella and chin, thick lips) and biochemical characteristics. Here, we present the variable expressivity in the two siblings.

Clinical Management in Systemic Type Pseudohypoaldosteronism Due to SCNN1B Variant and Literature Review

Systemic pseudohypoaldosteronism (PHA) is a rare, salt-wasting syndrome that is caused by inactivating variants in genes encoding epithelial sodium channel subunits. Hyponatremia, hyperkalemia, metabolic acidosis, increased aldosterone and renin levels are expected findings in PHA. Clinical management is challenging due to high dose oral replacement therapy. Furthermore, patients with systemic PHA require life-long therapy. Here we report a patient with systemic PHA due to SCNN1B variant whose hyponatremia and hyperkalemia was detected at the 24th hour of life. Hyperkalemia did not improve with conventional treatments and dialysis was required. He also developed myocarditis and hypertension in follow-up. Challenges for diagnosis and treatment in this patient are discussed herein. In addition, published evidence concerning common features of patients with SCNN1B variant are reviewed.

Further Phenotypic Delineation of Partial Trisomy 17q and Partial Monosomy 20q due to Rare t(17;20).

Copy number variations in subtelomeric regions of chromosomes 17 and 20 are associated with intellectual disability and various systemic manifestations. Microarray analysis allows identification of submicroscopic chromosomal abnormalities and is applicable to elucidate the etiology of cognitive impairment in approximately one-fifth of the cases. In the present study, we report on 3 male children from 2 sisters, who suffered from intellectual disability, facial dysmorphism, and epilepsy. Despite the initial suggestion of an X-linked inheritance, the condition was associated with 17q25.3 duplication and concomitant 20q13.33 deletion, as detected by microarray analysis. Coexistence of a deletion and a duplication suggests unbalanced segregation of a parental balanced translocation. Further investigations revealed maternal balanced translocations, which resulted in copy number aberrations in the children following unbalanced segregations. The work-up underlined the importance of genomic screening using microarrays as the first-tier diagnostic tool in intellectual disability, despite an apparent X-linked segregation in the pedigree.