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.

De novo interstitial deletion of 11q14.3q22 in a boy with mild intellectual disability and short stature.

BACKGROUND: Interstitial deletions of the 11q region are infrequent. Nonrecurrent chromosomal rearrangements are observed with high variability in size and precise breakpoints of the deleted area. Moreover heterogeneous clinical findings are observed in those harboring 11q interstitial deletions. Main clinical features associated with these deletions include mild dysmorphic findings intellectual disability and moderate developmental or speech delay . METHOD: Conventional high-resolution karyotyping along with microarray studies were performed for the index patient who was found to be a carrier of a de novo interstitial deletion in the long arm of chromosome 11 which is located between the 11q14 and 11q22 band regions. We also investigated the homologous chromosome with next-generation sequencing technology to search for unmasked recessive variants in genes on the nondeleted contralateral allele. RESULTS: Cytogenetic analysis revealed a de novo interstitial deletion on the long arm of chromosome 11 46 XY del(11) (q14q22). Microarray analysis confirmed the deletion of 11.2 Mb in length mapping from 11q14.3 to 11q22.2 [arr (GRCh37) 11q14.3q22.1(90549863_101833022)x1 dn]. Whole-exome sequencing did not detect any other genetic variant (single nucleotide variant ) on the nondeleted allele. CONCLUSION: This study gave us the opportunity for an attempt to define the smallest region of overlap for frequently observed clinical findings by reviewing the literature.

Renpenning Syndrome in a Turkish Patient: de novo Variant c.607C>T in PACS1 and Hypogammaglobulinemia Phenotype.

Renpenning syndrome is an X-linked intellectual disability syndrome caused by mutations in the human polyglutamine binding protein 1 (PQBP1) gene characterized by intellectual disability (ID), microcephaly, and dysmorphic facial features. We report a Turkish child with a novel pathogenic variant in PQBP1 and a likely pathogenic variant in the PACS1 gene presenting with growth restriction, microcephaly, ID, micropenis, bilateral iris coloboma, and hypogammaglobulinemia. Cytogenetic investigations, including a high-resolution-banded karyotype, were normal. Clinical exome sequencing was performed. We found the novel PQBP1 variant, c.640C>T; p.(Arg214Trp), and the known PACS1 variant, c.607C>T; p.(Arg203Trp), in the proband. The patient's hypogammaglobulinemia did not respond to treatment. This condition was detected for the first time in a patient with Renpenning syndrome.

Successful management of acute pancreatitis due to apolipoprotein C-II deficiency in a 37-day-old infant.

Familial chylomicronemia is caused by deficiency of lipoprotein lipase or its co-activators. Here, we report an infant with apolipoprotein C-II (APOC2) deficiency, who developed acute pancreatitis 37 days after birth. He presented as abdominal sepsis with fever, irritability and abdominal distention. Amylase levels were low, but lipase levels and imaging findings were consistent with acute pancreatitis. He had severe hypertriglyceridemia (1091 mg/dl). Keeping him nil orally for two days resulted in rapid decrease in triglyceride levels and resolution of the clinical findings. APOC2 gene sequencing revealed a homozygous splice-site mutation (c.55+1G>C). To the best of our knowledge, this patient is not only the youngest reported patient with APOC2 deficiency, but also the youngest such patient who developed pancreatitis. Although he had a severe presentation, invasive methods to treat hypertriglyceridemia were not necessary. We emphasize that clinical findings and amylase levels are not reliable to diagnose pancreatitis in this age group.

A Glutamine Repeat Variant of the RUNX2 Gene Causes Cleidocranial Dysplasia.

Cleidocranial dysplasia (CCD), an autosomal dominant skeletal dysplasia characterized by hypoplastic clavicles and delayed closure of the cranial sutures, is caused by mutations of the runt-related transcription factor 2 (RUNX2) gene. The RUNX2 gene consists of a glutamine and alanine repeat domain (Q/A domain, 23Q/17A), a DNA-binding Runt domain and a proline/serine/threonine-rich domain. We report on a familial case of CCD with a novel mutation within the Q/A domain of the RUNX2 gene, which is an insertion in exon 1 (p.Q71_E72insQQQQ) representing the Q-repeat variant (27Q/17A). Functional analysis of the 27Q variant revealed abolished transactivation capacity of the mutated RUNX2 protein. This is the first case report that demonstrated a glutamine repeat variant of the RUNX2 gene causes CCD.