Abnormal sebaceous gland differentiation in 10 kittens (‘sebaceous gland dysplasia’) associated with generalized hypotrichosis and scaling

SOAT1 missense variant in two cats with sebaceous gland dysplasia

Spontaneously arisen hereditary diseases in domestic animals provide an excellent opportunity to study the physiological functions of the altered genes. We investigated two 4-month-old sibling domestic short haired kittens with dry dark debris around the eyes, nose, and ears, dark crusting on the legs and a thin poor hair coat. Skin biopsies revealed abnormal sebaceous gland morphology with lack of normal sebocyte arrangement and differentiation. Hair follicles had a distorted silhouette, interpreted as a change secondary to the observed sebaceous gland dysplasia. Whole genome sequencing on both affected kittens and 65 genetically diverse feline genomes was performed. Filtering for variants that were present in both kittens but absent from the control genomes revealed a homozygous missense variant in SOAT1, encoding sterol O-acyltransferase 1. The protein is localized in the endoplasmic reticulum and catalyzes the formation of cholesteryl esters, an essential component of sebum and meibum. The identified SOAT1:c.1531G > A variant is predicted to change a highly conserved glycine residue within the last transmembrane domain of SOAT1, p.Gly511Arg. In mice, variants in Soat1 or complete knockout of the gene lead to the "hair interior defect" (hid) or abnormal Meibomian glands, respectively. SOAT1:c.1531G > A represents a plausible candidate variant for the observed sebaceous gland dysplasia in both kittens of this study. The variant was not present in 10 additional cats with a similar clinical and histopathological phenotype suggesting genetic heterogeneity. SOAT1 variants should be considered as potential cause in hereditary sebaceous gland dysplasias of humans and domestic animals.

Chronic Otitis in Cats: Clinical management of primary, predisposing and perpetuating factors

PRACTICAL RELEVANCE

Chronic otitis can be one of the most frustrating diseases to manage for a small animal practitioner. While it occurs less commonly in the cat than the dog, it is no less challenging. The purpose of this review is to discuss the common and uncommon causes of chronic otitis in the cat within the clinical framework used for diagnosis and treatment. The focus is on diseases that affect the ear canal, rather than those restricted to the pinnae.

CLINICAL CHALLENGES

Otitis is multifactorial, which complicates management. A common clinical mistake is to focus solely on treating the infection present. Only by addressing all factors will a clinician successfully control chronic otitis. For the purposes of this review, the authors have adopted the established model of separating primary, predisposing and perpetuating causes of otitis. Primary factors are those that directly cause otitis (inflammation); predisposing factors are those that put the patient at risk for development of otitis; and perpetuating factors are those that result in ongoing clinical signs of otitis or that prevent clinical resolution.

AUDIENCE

This review is aimed at veterinarians who treat cats and particularly those with an interest in feline dermatology and otology.

EQUIPMENT

While many practitioners rely on a hand-held otoscope, a video-otoscope can be very helpful for the diagnosis and treatment of chronic otitis.

EVIDENCE BASE

This review presents up-to-date information regarding the diagnosis and treatment of chronic otitis in cats, with emphasis on the most recent peer-reviewed literature.

Non-dermatophyte Dermatoses Mimicking Dermatophytoses in Animals

Dermatophytoses in animals are fungal diseases of the skin caused by dermatophyte fungi of the genus Microsporum or Trichophyton. Because the infection is generally follicular, the most common clinical sign is one or many circular areas of alopecia with variable erythema, scaling and crusting, and the primary differential diagnoses are follicular infections, such as bacterial folliculitis and demodicosis. Although dermatophyte folliculitis or ringworm is the most commonly observed lesion of dermatophytoses in animals, other presentations may be observed according to the host species and the dermatophyte involved: dermatophyte folliculitis or ringworm, scaling and crusting in dermatophytosis due to Microsporum persicolor, nodule in case of kerion or mycetoma, matted hairs, seborrheic dermatosis or miliary dermatitis in cats, generalized exfoliative dermatoses in dogs, cats and horses, superficial non-follicular pustules, papules and macules in the Devon Rex cat, pruritic dermatophytoses in dogs, cats and horses, and onychomycosis in dogs, cats and horses. Since manifestations of dermatophytosis are highly variable, particularly in the cat, dermatophytosis should be considered in case of any annular, papular, nodular or pustular dermatoses, alopecic or not, sometimes pruritic, and nodular dermatoses as well.

Alopecia in four kittens caused by abnormal maternal licking behaviour

CASE REPORT

Abnormal maternal behaviour has been reported in cats, but is generally not included among the causes of alopecia in kittens. A litter of four kittens, 2 months old, was referred for evaluation of facial alopecia of differing severity. The 2-year-old queen was unaffected. Dermatological examination of the kittens did not find any infectious cause. Trichograms showed broken hair shafts with longitudinal splitting. Congenital alopecia was unlikely based on the clinical presentation. A behavioural consultation revealed abnormal grooming behaviour by the mother, who chewed and removed the hair from the kittens. The kittens were separated from the queen and alopecia resolved within a few weeks.

CONCLUSION

To the authors' knowledge, this is the first report of alopecia caused by abnormal maternal licking behaviour. Abnormal maternal behaviour should be considered in cases of alopecia affecting a litter of kittens, when infectious and congenital causes have been ruled out.

Scaling dermatosis in three dogs associated with abnormal sebaceous gland differentiation

BACKGROUND

Abnormal sebaceous gland differentiation, so-called 'sebaceous gland dysplasia', is a rare condition described in the dog and the cat. Although little is known about this condition, it is thought that a genetic defect causes abnormal sebaceous gland development. Clinically, this condition occurs in young cats and dogs and is characterized by variable degrees of adherent scale, hair casts, poor coat quality and hypotrichosis.

HYPOTHESIS/OBJECTIVE

Here, we describe the clinical presentation and treatment of three adult dogs with abnormal sebaceous gland differentiation.

ANIMALS

Three adult dogs presented with a keratinization defect characterized by progressive scaling, hair casts, dull, dry, brittle hair coat and hypotrichosis beginning in puppyhood to early adulthood.

METHODS

Multiple 6 mm punch skin biopsy samples were obtained from each dog. Treatments included various topical keratomodulatory agents, oral essential fatty acids and oral vitamin A.

RESULTS

Histologically, all sebaceous glands were small and composed of a mixture of irregularly clustered basal reserve cells and mature sebocytes. With therapy, two of the dogs showed moderate to marked clinical improvement in scaling, hair casts and hair coat quality.

CONCLUSIONS AND CLINICAL IMPORTANCE

Although rare, 'sebaceous gland dysplasia' should be considered in cases where a primary keratinization defect is suspected. Given that abnormal sebaceous differentiation is a structural defect of the skin, treatment must be maintained and is aimed at ameliorating the clinical signs rather than curing the disease.