Intermediate severe Salla Disease in differential diagnosis of hypomyelinating leukodystrophy: the second and third case from Turkey

Objectives Sialic acid storage disorder (SSD) is a rare autosomal recessive lysosomal disorder caused by mutations in the SLC17A5 gene encoding the lysosomal transport protein sialin. According to the age and severity of the findings, the disease is classified into three types as conventional form of SD (Salla disease), intermediate severe SD, and infantile SD. Methods We present clinical, genetic and radiological findings of a girl with intermediate severe SD. Results A 5-year-old female born from consanguineous parents presented with a complaint of delayed speech, gait disturbance and tremor. Systemic and neurological examinations were normal except for ataxic gait and titubation. Although all laboratory and metabolic screening tests were normal, urine sialic acid analysis could not be performed. Brain magnetic resonance imaging showed hypomyelinating leukodystrophy. İllumina TruSight Inherited Disease panel including 552 genes for mutations related to AR pediatric-onset diseases was performed for investigation of the causes of hypomyelinating leukodystrophy. Homozygous SCL175A5NM 01234: exon3: c: A406G: p.K136E mutation was detected and the patient was diagnosed with intermediate severe SD. This mutation was also detected in her sister with similar symtoms. Her parents also has same mutation in a heterozygous form. Conclusions Our patient is the second Turkish case diagnosed with intermediate severe SD in the literature. Intermediate severe SD should be kept in mind in the differential diagnosis of hypomyelinating leukodystrophy.
Keywords: hypomyelinating, leukodystrophy, Salla Disease