Johanson-Blizzard syndrome with mild phenotypic features confirmed by UBR1 gene testing.

Johanson-Blizzard syndrome (JBS) is a rare autosomal recessive condition associated with exocrine pancreatic insufficiency, and is characterized by hypoplastic nasal alae, mental retardation, sensorineural hearing loss, short stature, scalp defects, dental abnormalities and abnormal hair patterns. Growth hormone deficiency, hypopituitarism, and impaired glucagon secretion response to insulin-induced hypoglycemia have been reported. Congenital heart defects have also been described in this condition.

Johanson-Blizzard syndrome caused by identical UBR1 mutations in two unrelated girls, one with a cardiomyopathy.

We report on two apparently unrelated girls with Johanson-Blizzard syndrome (JBS), in both children caused by a homozygous IVS26+5G>A mutation in the UBR1 gene. In both cases the parents are consanguineous and more sibs are affected. The somewhat mild phenotype (with no or slight mental retardation) in these two JBS families might be explained by residual UBR1 activity.

SOS1 is the second most common Noonan gene but plays no major role in cardio-facio-cutaneous syndrome.

Background: Heterozygous gain-of-function mutations in various genes encoding proteins of the Ras-MAPK signalling cascade have been identified as the genetic basis of Noonan syndrome (NS) and cardio-facio-cutaneous syndrome (CFCS). Mutations of SOS1, the gene encoding a guanine nucleotide exchange factor for Ras, have been the most recent discoveries in patients with NS, but this gene has not been studied in patients with CFCS.

Methods And Results: We investigated SOS1 in a large cohort of patients with disorders of the NS-CFCS spectrum, who had previously tested negative for mutations in PTPN11, KRAS, BRAF, MEK1 and MEK2.