CTNS Mutations in African American Patients with Cystinosis

doi:10.1006/mgme.2001.3218

Molecular Genetics and Metabolism

Volume 74, Issue 3, November 2001, Pages 332-337

https://doi.org/10.1006/mgme.2001.3218 Get rights and content

Abstract

Cystinosis, an autosomal recessive lysosomal storage disorder, is rarely diagnosed in African Americans. The disease results from mutations in the gene CTNS; at least 55 such mutations have been reported. By far the most common is a 57,257-bp deletion of Northern European origin encompassing most of the CTNS gene. We performed mutation analysis on DNA from four African American patients with cystinosis. In one individual with classical, nephropathic cystinosis, we identified a new molecular defect, i.e., a homozygous GT→CC substitution at the +5 position of IVS 5 of CTNS (IVS 5+5 GT→CC). The out-of-frame splicing of exon 5 creates a null allele consistent with the patient's severe phenotype. Two patients were heterozygous and one homozygous for the common 57-kb deletion allele, reflecting the admixture of African and Northern European gene pools in North America. The two African Americans heterozygous for the 57-kb deletion were also hemizygous for a 928G→A change, associated with ocular or nonnephropathic cystinosis. These two individuals are the only known African Americans with ocular cystinosis. We conclude that the diagnosis of cystinosis should be entertained in African Americans with symptoms of the disease, and that mutation analysis for the 57-kb deletion should be considered in this group of patients.

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Cited by (29)

CTNS molecular genetics profile in a Persian nephropathic cystinosis population
2017, Nefrologia
Citation Excerpt :
The CTNS gene has 13 exons, but exons 3–12 are protein-coding; biallelic mutations lead to significant loss of the lysosomal cystine transporter, cystinosin.3,7–9 Approximately 200 CTNS mutations have been reported in cystinosis patients, the most common is a 57-kb deletion responsible for 50% of all the North American and Northern European cases.10–20 Here we report the CTNS mutations present in 28 Iranian patients of diverse ethnicity, providing the first molecular genetic study of cystinosis in this population.
In this report, we document the CTNS gene mutations of 28 Iranian patients with nephropathic cystinosis age 1–17 years. All presented initially with severe failure to thrive, polyuria, and polydipsia.
Cystinosis was primarily diagnosed by a pediatric nephrologist and then referred to the Iran University of Medical Sciences genetics clinic for consultation and molecular analysis, which involved polymerase chain reaction (PCR) amplification to determine the presence or absence of the 57-kb founder deletion in CTNS, followed by direct sequencing of the coding exons of CTNS.
The common 57-kb deletion was not observed in any of the 28 Iranian patients. In 14 of 28 patients (50%), mutations were observed in exons 6 and 7. No mutation was detected in exon 5, and only one (3.6%) patient with cystinosis showed a previously reported 4-bp deletion in exon 3 of CTNS. Four patients (14.3%) had a previously reported mutation (c.969C>A; p.N323K) in exon 11, and five (18%) had novel homozygous deletions in exon 6 leading to premature truncation of the protein. These deletions included c.323delA; p.Q108RfsX10 in three individuals and c.257-258delCT; p.S86FfsX37 in two cases. Other frame-shift mutations were all novel homozygous single base pair deletion/insertions including one in CTNS exon 9 (c.661insT; p.V221CfsX6), and four (14.3%) in exon 4, i.e., c.92insG; p.V31GfsX28 in two and c.120delC; p.T40TfsX10 in two. In total, we identified eight previously reported mutations and eight novel mutations in our patients. The only detected splice site mutation (IVS3-2A>C) was associated with the insertion mutation in the exon 9.
This study, the first molecular genetic analysis of non-ethnic-specific Iranian nephropathic cystinosis patients, may provide guidance for molecular diagnostics of cystinosis in Iran.
En este informe, documentamos las mutaciones del gen CTNS de 28 pacientes iraníes con cistinosis nefropática y una edad de 1-17 años. En un principio, todos presentaron retraso del desarrollo, poliuria y polidipsia.
En primer lugar, un nefrólogo pediátrico diagnosticó la cistinosis y luego los pacientes fueron trasladados a la clínica genética de la Universidad de Ciencias Médicas de Irán para consulta y análisis molecular, que incluía la multiplicación por reacción en cadena de la polimerasa (PCR), para determinar la existencia o ausencia de la deleción del fundador del 57 kb en el CTNS, seguida por la secuenciación directa de los exones de codificación del CTNS.
La deleción frecuente del 57 kb no se observó en ninguno de los 28 pacientes iraníes. En 14 de los 28 pacientes (50%) se observaron mutaciones en los exones 6 y 7. No se detectó ninguna mutación en el exón 5 y solo un paciente (3,6%) con cistinosis mostró una deleción del 4 pb, anteriormente comunicada, en el exón 3 del CTNS. De ellos, 4 pacientes (14,3%) tenían una mutación anteriormente comunicada (c.969C > A; p.N323 K) en el exón 11 y 5 (18%) tenían nuevas deleciones homocigóticas en el exón 6 que produjeron el vaciamiento prematuro de la proteína. Entre estas deleciones se puede citar c.323delA; p.Q108RfsX10 en 3 personas y c.257-258delCT; p.S86FfsX37 en 2 casos. Otras mutaciones con desplazamiento del marco de lectura fueron todas nuevas deleciones/inserciones de un par de bases únicas homocigóticas, incluyendo una en el exón 9 del CTNS (c.661insT; p.V221CfsX6) y 4 (14,3%) en el exón 4, es decir, c.92insG; p.V31GfsX28 en 2 y c.120delC; p.T40TfsX10 en 2. En total, en nuestros pacientes se identificaron 8 mutaciones anteriormente comunicadas y 8 mutaciones nuevas. La única mutación del sitio de empalme detectada (IVS3-2A > C) estaba asociada con la mutación de inserción en el exón 9.
Este estudio, el primer análisis genético molecular de pacientes iraníes con cistinosis nefropática de carácter no específicamente étnico, puede servir como guía para el diagnóstico molecular de la cistinosis en Irán.
CTNS mutations in publicly-available human cystinosis cell lines
2015, Molecular Genetics and Metabolism Reports
Citation Excerpt :
In order to confirm that these mutations are the reason for observed nephropathic cystinosis diagnosis it was necessary to determine if: 1) the novel variant affects normal synthesis of cystinosin protein; 2) both variants are located on different alleles. Novel variant c.225 + 5G > A is overlapping with the previously characterized cystinosis mutation c.225 + 5GT > CC, which leads to skipping of exon 5 [9]. Therefore, we decided to check for the presence of exon 5 in GM02066 by designing primers flanking the exon borders.
Patient samples play an important role in the study of inherited metabolic disorders. Open-access biorepositories distribute such samples. Unfortunately, not all clinically-characterized samples come with reliable genotype information. During studies directed toward population frequency assessments of cystinosis, a rare heritable disorder, we sequenced the CTNS gene from 14 cystinosis-related samples obtained from the Coriell Cell Repository. As a result, the disease genotypes of 7 samples were determined for the first time. The reported disease genotypes of 2 additional samples were found to be incorrect. Furthermore, we identified and experimentally confirmed a novel mutation, c.225 + 5G > A, which causes skipping of the 5th exon and is associated with infantile nephropathic cystinosis.
Hereditary Cystinosis
2009, Genetic Diseases of the Kidney
This chapter reviews the most recent advances in the molecular biology of cystinosis, focuses on the causative CTNSmutations identified to date, and explains a correlation between genotype and the differing clinical phenotypes. Cystinosis is a rare autosomal recessive monogenic disorder with an incidence of ~1/200,000 live births, characterized by an intralysosomal accumulation of cystine. It constitutes the most common familial form of the renal Fanconi syndrome. The underlying metabolic defect of cystinosis is an accumulation of cystine in the lysosomes. Cystine, the disulfide of the amino acid cysteine, is a by-product of lysosomal protein hydrolysis, and is reduced to cysteine in the cytoplasm. Lysosome hydrolases, responsible for the digestion of macromolecules, have optimal activity at acid pH and the acidification of the lysosomal lumen is accomplished by the presence of an ATPase H+-pump in its membrane. In the case of cystinosis, the lysosomal cystine transporter is defective leading to an abnormal storage of cystine. It is due to its poor solubility that cystine forms crystals as its concentration increases. A measure of leukocyte cystine levels using a cystine binding protein assay is generally used to confirm a suspicion of cystinosis. Oral cysteamine therapy, if administered early in the course of the disease and in high doses, delays the progression of renal insufficiency. In addition, it prevents the appearance of hypothyroidism, and decreases the severity of oral motor and swallowing dysfunction, which is correlated with generalized muscle atrophy. Approximately 90 different CTNSmutations have been detected in all forms of cystinosis up to now. Many of the point mutations associated with the infantile form are deletions, insertions, and splice site mutations that cause premature termination of cystinosin.
Nodular regenerative hyperplasia and severe portal hypertension in cystinosis
2006, Clinical Gastroenterology and Hepatology
Background & Aims: Cystinosis is a rare autosomal-recessive disorder characterized by the intralysosomal accumulation of cystine, which is responsible for widespread tissue destruction. Liver biopsy specimens of patients with cystinosis show cystine crystal formation in Kupffer cells. However, significant liver disease and portal hypertension is not a common complication of cystinosis. We report the case histories of 2 young men with poorly treated nephropathic cystinosis who developed noncirrhotic portal hypertension with evidence of nodular regenerative hyperplasia (NRH). Methods: Liver biopsy examinations, upper and lower endoscopy with biopsy examination, imaging studies, venous pressure measurements, and laboratory investigations were used to evaluate the causes of the liver disease and portal hypertension. Results: Histologic examination of liver biopsy specimens from both patients showed changes characteristic of NRH with portal hypertension documented by measurement of pressure gradients. In addition, endoscopy in the first patient showed varices and portal hypertensive gastropathy. Conclusions: NRH was confirmed by histologic examination of the liver in both patients and is the likely cause of their portal hypertension. NRH may represent a rare, late complication of cystinosis, although the mechanism remains undefined.
Long-term follow-up of well-treated nephropathic cystinosis patients
2004, Journal of Pediatrics
Citation Excerpt :
The Fanconi Syndrome Index (FSI), a quantitative measure of aminoaciduria, was determined by measuring the daily urinary excretion of 21 specific amino acids.31 Molecular studies of CTNS were performed as described.32 In short, genomic DNA was isolated from whole blood following standard procedures.
Genetic Landscape of Nephropathic Cystinosis in Russian Children
2022, Frontiers in Genetics

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¹: To whom correspondence should be addressed at 10 Center Drive, MSC 1830, Building 10, Room 9S-241, NICHD, NIH, Bethesda, MD 20892-1830. Fax: (301)-402-0234. E-mail: [email protected].

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Regular ArticleCTNS Mutations in African American Patients with Cystinosis

Abstract

J Biol Chem

J Biol Chem

Adv Pediatr

J Pediatr

Chest

Am J Hum Genet

Am J Hum Genet

Mol Genet Metab

J Pediatr

Mol Genet Metab

J Biol Chem

Cystine transport is defective in isolated leukocyte lysosomes from patients with cystinosis

Science

Cystinosis: A disorder of lysosomal membrane transport

Cystinosis: A treatable lysosomal storage disease

Endocrinologist

Distal vacuolar myopathy in nephropathic cystinosis

Ann Neurol

Swallowing dysfunction in nephropathic cystinosis

N Engl J Med

Pancreatic endocrine insufficiency in post-transplant cystinosis

Am J Dis Child

Evidence for cerebral involvement in nephropathic cystinosis

Neuropaediatrie

Regular Article
CTNS Mutations in African American Patients with Cystinosis