Coexistence of Megaconial Congenital Muscular Dystrophy and Cystinuria: Mimicking Hypotonia-Cystinuria Syndrome

Introduction: Hypotonia-cystinuria syndrome is a contiguous gene deletion syndrome that is characterized by hypotonia, developmental delay, and cystinuria type A. We present a male patient who was admitted to our center with clinical findings of hypotonia-cystinuria syndrome and diagnosed with megaconial congenital muscular dystrophy and cystinuria. Case Presentation: A 16-month-old male patient was admitted with complaints of restlessness and body laxity. It was stated that the patient had hypotonia and growth retardation at the age of 2 months. Physical examination revealed mild hypotonia, growth retardation, and development delay, while laboratory examinations identified elevated serum creatine kinase and elevated dibasic amino acid in urine analysis. Because of the findings of hypotonia, growth retardation, developmental delay, and cystinuria, hypotonia-cystinuria syndrome was considered as a differential diagnosis. However, by chromosomal microarray no contiguous deletion in region 2p21 was found, while a novel homozygous c.225-2A>T pathogenic variant in the CHKB gene and a c.1266_1267delGT heterozygous variant in the SLC7A9 gene inherited from the mother were identified with whole-exome sequencing. The co-occurrence of megaconial congenital muscular dystrophy and cystinuria, mimicking hypotonia-cystinuria syndrome, was confirmed. Conclusion: This case suggests that in countries with a high frequency of consanguineous marriage, even if the molecular genetic analysis results are not compatible with the clinical findings, it should be kept in mind that different genetic diseases may coexist.