An unusual case of Pseudohypoaldosteronism coexisting with cystic fibrosis.

Pseudohypoaldosteronism type 1 is a rare congenital autosomal recessive disorder, characterised by failure of receptor response to aldosterone. It is caused by mutation in SCNN1A gene with clinical features like failure to thrive in infancy, hyponatraemia, hyperkalaemia and metabolic acidosis. We present a male infant with seizures, hyperkalaemia and with failure to thrive, diagnosed at day 6 of life. The baby required repeated correction for hyperkalaemia; hence, after ruling out treatable causes for hyperkalaemia, exonerated sequencing was done which showed pathogenic mutation for cystic fibrosis and recessive mutation for pseudohypoaldosteronism. But the child was clinically in favour of pseudohypoaldosteronism. Hence, features of pseudohypoaldosteronism predominate cystic fibrosis; they both may coexist.

Epilepsy in KCNH1-related syndromes.

KCNH1 mutations have been identified in patients with Zimmermann-Laband syndrome and Temple-Baraitser syndrome, as well as patients with uncharacterized syndromes with intellectual disability and overlapping features. These syndromes include dysmorphic facial features, nail hypo/aplasia, thumb and skeletal anomalies, intellectual disability, and seizures. We report the epilepsy phenotype in patients with KCNH1 mutations. Demographic data, electroclinical features, response to antiepileptic drugs, and results of significant diagnostic investigations of nine patients carrying mutations in KCNH1 were obtained from referring centres. Epilepsy was present in 7/9 patients. Both generalized and focal tonic-clonic seizures were observed. Complete seizure control was achieved with pharmacological treatment in 2/7 patients; polytherapy was required in 4/7 patients. Status epilepticus occurred in 4/7 patients. EEG showed a diffusely slow background in 7/7 patients with epilepsy, with variable epileptiform abnormalities. Cerebral folate deficiency and an increase in urinary hypoxanthine and uridine were observed in one patient. Epilepsy is a key phenotypic feature in most individuals with KCNH1-related syndromes, suggesting a direct role of KCNH1 in epileptogenesis, although the underlying mechanism is not understood.

Mutations in KCNH1 and ATP6V1B2 cause Zimmermann-Laband syndrome.

Zimmermann-Laband syndrome (ZLS) is a developmental disorder characterized by facial dysmorphism with gingival enlargement, intellectual disability, hypoplasia or aplasia of nails and terminal phalanges, and hypertrichosis. We report that heterozygous missense mutations in KCNH1 account for a considerable proportion of ZLS. KCNH1 encodes the voltage-gated K(+) channel Eag1 (Kv10.1). Patch-clamp recordings showed strong negative shifts in voltage-dependent activation for all but one KCNH1 channel mutant (Gly469Arg). Coexpression of Gly469Arg with wild-type KCNH1 resulted in heterotetrameric channels with reduced conductance at positive potentials but pronounced conductance at negative potentials. These data support a gain-of-function effect for all ZLS-associated KCNH1 mutants. We also identified a recurrent de novo missense change in ATP6V1B2, encoding the B2 subunit of the multimeric vacuolar H(+) ATPase, in two individuals with ZLS. Structural analysis predicts a perturbing effect of the mutation on complex assembly. Our findings demonstrate that KCNH1 mutations cause ZLS and document genetic heterogeneity for this disorder.