Skin and hair abnormalities of Cantu syndrome: A congenital hypertrichosis due to a genetic alteration mimicking the pharmacological effect of minoxidil

Cantú syndrome: A new case and evolution of clinical conditions during first 2-year follow-up

Cantú syndrome, or hypertrichotic osteochondrodysplasia, is a rare autosomal dominant disease characterized by congenital hypertrichosis, characteristic dysmorphisms, skeletal abnormalities and cardiomegaly. We report on a 7-year-old girl with congenital generalized hypertrichosis, coarse facial appearance and cardiac involvement, with a de novo heterozygous mutation (c.3461G > A) in the ABCC9 gene. During the annual cardiac follow-up at the age of nine the echocardiogram showed mild left ventricular dilatation in consideration of which she started ramipril treatment. The progression of the clinical manifestations of Cantú syndrome highlights the relevance of an early diagnosis, including genetic analysis, and a multidisciplinary approach with long-term follow-up.

Update of recent findings in genetic hair disorders

Genetic hair disorders, although unusual, are not very rare, and dermatologists often have opportunities to see patients. Significant advances in molecular genetics have led to identifying many causative genes for genetic hair disorders, including the recently identified causative genes, such as LSS and C3ORF52. Many patients have been detected with autosomal recessive woolly hair/hypotrichosis in the Japanese population caused by founder mutations in the LIPH gene. Additionally, many patients with genetic hair disorders caused by other genes have been reported in East Asia including Japan. Understanding genetic hair disorders is essential for dermatologists, and the findings obtained from analyzing these diseases will contribute to revealing the mechanisms of hair follicle morphogenesis and development in humans.

Recurrent KCNT2 missense variants affecting p.Arg190 result in a recognizable phenotype

KCNT2 variants resulting in substitutions affecting the Arg190 residue have been shown to cause epileptic encephalopathy and a recognizable facial gestalt. We report two additional individuals with intellectual disability, dysmorphic features, hypertrichosis, macrocephaly and the same de novo KCNT2 missense variants affecting the Arg190 residue as previously described. Notably, neither patient has epilepsy. Homology modeling of these missense variants revealed that they are likely to disrupt the stabilization of a closed channel conformation of KCNT2 resulting in a constitutively open state. This is the first report of pathogenic variants in KCNT2 causing a developmental phenotype without epilepsy.

Syndromic disorders caused by gain-of-function variants in KCNH1, KCNK4, and KCNN3-a subgroup of K+ channelopathies

Decreased or increased activity of potassium channels caused by loss-of-function and gain-of-function (GOF) variants in the corresponding genes, respectively, underlies a broad spectrum of human disorders affecting the central nervous system, heart, kidney, and other organs. While the association of epilepsy and intellectual disability (ID) with variants affecting function in genes encoding potassium channels is well known, GOF missense variants in K⁺ channel encoding genes in individuals with syndromic developmental disorders have only recently been recognized. These syndromic phenotypes include Zimmermann–Laband and Temple–Baraitser syndromes, caused by dominant variants in KCNH1, FHEIG syndrome due to dominant variants in KCNK4, and the clinical picture associated with dominant variants in KCNN3. Here we review the presentation of these individuals, including five newly reported with variants in KCNH1 and three additional individuals with KCNN3 variants, all variants likely affecting function. There is notable overlap in the phenotypic findings of these syndromes associated with dominant KCNN3, KCNH1, and KCNK4 variants, sharing developmental delay and/or ID, coarse facial features, gingival enlargement, distal digital hypoplasia, and hypertrichosis. We suggest to combine the phenotypes and define a new subgroup of potassium channelopathies caused by increased K⁺ conductance, referred to as syndromic neurodevelopmental K⁺ channelopathies due to dominant variants in KCNH1, KCNK4, or KCNN3.

Cantú syndrome versus Zimmermann-Laband syndrome: Report of nine individuals with ABCC9 variants

Cantú syndrome (CS) is a rare developmental disorder characterized by a coarse facial appearance, macrocephaly, hypertrichosis, skeletal and cardiovascular anomalies and caused by heterozygous gain-of-function variants in ABCC9 and KCNJ8, encoding subunits of heterooctameric ATP-sensitive potassium (K_ATP) channels. CS shows considerable clinical overlap with Zimmermann-Laband syndrome (ZLS), a rare condition with coarse facial features, hypertrichosis, gingival overgrowth, intellectual disability of variable degree, and hypoplasia or aplasia of terminal phalanges and/or nails. ZLS is caused by heterozygous gain-of-function variants in KCNH1 or KCNN3, and gain-of-function KCNK4 variants underlie the clinically similar FHEIG (facial dysmorphism, hypertrichosis, epilepsy, intellectual disability/developmental delay, and gingival overgrowth) syndrome; KCNH1, KCNN3 and KCNK4 encode potassium channels. Within our research project on ZLS, we performed targeted Sanger sequencing of ABCC9 in 15 individuals tested negative for a mutation in the ZLS-associated genes and found two individuals harboring a heterozygous pathogenic ABCC9 missense variant. Through a collaborative effort, we identified a total of nine individuals carrying a monoallelic ABCC9 variant: five sporadic patients and four members of two unrelated families. Among the six detected ABCC9 missense variants, four [p.(Pro252Leu), p.(Thr259Lys), p.(Ala1064Pro), and p.(Arg1197His)] were novel. Systematic assessment of the clinical features in the nine cases with an ABCC9 variant highlights the significant clinical overlap between ZLS and CS that includes early developmental delay, hypertrichosis, gingival overgrowth, joint laxity, and hypoplasia of terminal phalanges and nails. Gain of K⁺ channel activity possibly accounts for significant clinical similarities of CS, ZLS and FHEIG syndrome and defines a new subgroup of potassium channelopathies.