A sporadic case of cystinuria, respiratory chain and growth hormone deficiencies

Hypotonia-cystinuria 2p21 deletion syndrome: Intrafamilial variability of clinical expression

Two siblings presented similarly with congenital hypotonia, lactic acidosis, and failure to thrive. Later in childhood, the brother developed cystinuria and nephrolithiasis whereas the older sister suffered from cystinuria and chronic neurobehavioral disturbances. Biopsied muscle studies demonstrated deficient cytochrome c oxidase activities consistent with a mitochondrial disease. Whole exome sequencing (WES), however, revealed a homozygous 2p21 deletion involving two contiquous genes, SLC3A1 (deletion of exons 2‐10) and PREPL (deletion of exons 2‐14). The molecular findings were consistent with the hypotonia–cystinuria 2p21 deletion syndrome, presenting similarly in infancy with mitochondrial dysfunction but diverging later in childhood and displaying intrafamilial phenotypic variability.

First cardiac manifestation of hypotonia-cystinuria syndrome

Hypotonia-cystinuria syndrome is a very rare autosomal recessive contiguous gene deletion syndrome of PREPL and SLC3A1 at 2p21 with neuromuscular and neuroendocrinologic presentation. We report a two-year-six-month-old affected female infant and her five-month-old affected brother with a novel homozygous deletion in SLC3A1 and PREPL gene. Both of siblings had mild facial dysmorphism, hypotonia, feeding problems, failure to thrive, developmental delay. She also had dilated cardiomyopathy which differ from other reported patients. Therefore cardiomyopathy may also be considered one of the features of hypotonia-cystinuria syndrome. With this case report, we present cardiac manifestation of hypotonia-cystinuria syndrome for the first time. Because of two siblings had hyperechogenic bowel in prenatal sonography, it might be a prenatal marker for HCS.

Further delineation of genotype-phenotype correlation in homozygous 2p21 deletion syndromes: first description of patients without cystinuria

Homozygous contiguous gene deletion syndromes are rare. On 2p21, however, several overlapping homozygous gene deletion syndromes have been described, all presenting with cystinuria but otherwise distinct phenotypes. Hypotonia-cystinuria syndrome (HCS, OMIM606407) is characterized by infantile hypotonia, poor feeding, and growth hormone deficiency. Affected individuals carry homozygous deletions including the cystinuria gene SLC3A1 and the adjacent PREPL gene. Larger homozygous deletions in this region encompassing the PPM1B, SLC3A1, PREPL, and C2orf34 (CAMKMT) genes result in a more severe phenotype, the 2p21 deletion syndrome. A phenotype intermediate to HCS and the 2p21 deletion syndrome is termed atypical HCS and is caused by deletion of SLC3A1, PREPL, and C2orf34 (CAMKMT). Using high resolution SNP array molecular karyotyping we identified two siblings with a homozygous deletion of 83 kb partially encompassing the genes PREPL and C2orf34 (CAMKMT), but not the SLC3A1 gene. The affected siblings display a recognizable phenotype which is similar to atypical HCS with regard to growth failure and neuro-muscular features, but is characterized by lack of cystinuria. The patients also exhibit features which have not been reported to date such as cleft palate and genital abnormalities. In conclusion, we report the first patients with a homozygous 2p21 deletion syndrome without cystinuria and further delineate the complex genotype-phenotype correlations of homozygous microdeletion syndromes of this region.

Deletion of C2orf34, PREPL and SLC3A1 causes atypical hypotonia-cystinuria syndrome

Hypotonia-cystinuria syndrome (HCS) and 2p21 deletion syndrome are two recessive contiguous gene deletion syndromes associated with cystinuria type I. In HCS patients, only SLC3A1 and PREPL are disrupted. In the 2p21 deletion syndrome, two additional genes (C2orf34 and PPM1B) are lost. Molecular analysis of the SLC3A1/PREPL locus was performed in the patients using quantitative polymerase chain reaction (PCR) methods. HCS in both siblings was confirmed with the deletion screen of the SLC3A1/PREPL locus. Fine mapping of the breakpoint revealed a deletion of 77.4 kb, including three genes: SLC3A1, PREPL and C2orf34. Features not present in classical HCS were a mild/moderate mental retardation and a respiratory chain complex IV deficiency. We report the first patients with a deletion of SLC3A1, PREPL and C2orf34. They present with a phenotype intermediate between HCS and 2p21 deletion syndrome.

Global distribution of the most prevalent deletions causing hypotonia-cystinuria syndrome

Hypotonia-cystinuria syndrome (HCS) is a recessive disorder caused by microdeletions of SLC3A1 and PREPL on chromosome 2p21. Patients present with generalized hypotonia at birth, failure to thrive, growth retardation and cystinuria type I. While the initially described HCS families live in small regions in Belgium and France, we have now identified HCS alleles in patients and carriers from the Netherlands, Italy, Canada and United States of America. Surprisingly, among the nine deletions detected in those patients, only one novel deletion was found. Furthermore, one previously described deletion was found six times, another twice. Finally, we have investigated the frequency of both deletions using a random Belgian cohort. Given the global occurrence, HCS should be considered in the differential diagnosis of neonatal hypotonia.

Genetic kidney diseases in the pediatric population of southern Israel

Genetic kidney diseases (GKDs) are an important and well-known entity in pediatric nephrology. In the past decade advances in genetic and molecular approaches have enabled elucidation of the underlying molecular defects in many of these disorders. Herein we summarize the progress that has been made over the past decade in disclosing the molecular basis of several novel GKDs, which were characterized in our area and include Bartter syndrome type IV, type II Bartter syndrome and transient neonatal hyperkalemia, cystinuria and mental retardation, familial hypomagnesemia with secondary hypocalcemia, infantile nephronophthisis, familial hemolytic uremic syndrome with factor H deficiency, and non-cystic autosomal dominant nephropathy. Retrospective analysis of our data reveals that GKDs are over-represented among the pediatric population in southern Israel. GKDs are seen four-times more often than end-stage renal disease (ESRD) and comprise 38% of all cases of ESRD in our area. This high rate of GKDs is mainly due to the high frequency of consanguineous marriages that prevails in this area. Understanding of the genetic and molecular background of these diseases is a result of a fruitful collaboration between the pediatric nephrologists and scientists, and has a direct implication on the diagnosis and treatment of the affected families.

PREPL: a putative novel oligopeptidase propelled into the limelight

The prolyl endopeptidase-like protein PREPL has recently attracted attention because its gene is located within two contiguous gene-deletion syndromes, the 2p21 deletion syndrome and the hypotonia-cystinuria syndrome. Deletion of the gene results in hypotonia at birth, failure to thrive and growth hormone deficiency. PREPL is highly reactive against an activity-based probe, which indicates the presence of an intact catalytic machinery. However, no substrate has been found yet. The unique carboxy-terminus of the catalytic domain might contain the key to the as yet elusive specificity.

Deletion of PREPL, a gene encoding a putative serine oligopeptidase, in patients with hypotonia-cystinuria syndrome

In 11 patients with a recessive congenital disorder, which we refer to as "the hypotonia-cystinuria syndrome," microdeletion of part of the SLC3A1 and PREPL genes on chromosome 2p21 was found. Patients present with generalized hypotonia at birth, nephrolithiasis, growth hormone deficiency, minor facial dysmorphism, and failure to thrive, followed by hyperphagia and rapid weight gain in late childhood. Since loss-of-function mutations in SLC3A1 are known to cause isolated cystinuria type I, and since the expression of the flanking genes, C2orf34 and PPM1B, was normal, the extended phenotype can be attributed to the deletion of PREPL. PREPL is localized in the cytosol and shows homology with prolyl endopeptidase and oligopeptidase B. Substitution of the predicted catalytic residues (Ser470, Asp556, and His601) by alanines resulted in loss of reactivity with a serine hydrolase-specific probe. In sharp contrast to prolyl oligopeptidase and oligopeptidase B, which require both aminoterminal and carboxyterminal sequences for activity, PREPL activity appears to depend only on the carboxyterminal domain. Taken together, these results suggest that PREPL is a novel oligopeptidase, with unique structural and functional characteristics, involved in hypotonia-cystinuria syndrome.