Following normal vaginal delivery at home with no pre-natal care, development had been limited to social smiling, sufficient fine motor skills to feed herself, infrequent speech of only single words, and an unsteady gait. Although a generally happy and smiling child, the patient had never been self-caring with regard to dressing and toileting, and was still wearing nappies.

She had 2 normal siblings, and there was no family history or other past medical history of note. The mother denied any consanguinity in the patient's recent lineage.

On examination the patient was smiling and playful, and appeared well-nourished. Large hyperkeratotic lesions were present on the cheeks and nose with some induration suspicious of actinic keratosis and early squamous cell carcinoma. There were also numerous hyper-pigmented lentigos and xerosis limited to sun-exposed sites. Marked corneal scarring was evident bilaterally (Figures ​(Figures1,1, ​,2,2, ​,3).3). There was no evidence of anaemia or overt signs of vitamin deficiencies such as rickets, and the mother and siblings appeared well nourished.

Physical examination of the heart, lungs and abdomen was unremarkable. There was mild choreoathetosis of the right arm, and gait was broad-based and grossly ataxic. Eye movements exhibited rolling nystagmus, but were able to track large objects. The patient was constantly reaching to the ground, trying to pick up things and put them in her mouth – either a neuro-developmental problem, or possibly indicative of pica. Unfortunately no laboratory testing was available for further investigation.

Given the cutaneous, neurological and ocular features a presumptive diagnosis of Xeroderma Pigmentosum was made. As facilities for pathological diagnosis were not available an opinion was sought from international colleagues. There was consensus that the clinical features were those of a photosensitive dermatoses with Xeroderma Pigmentosum being the most likely given the striking cutaneous features.

From an early age patients are sensitive to even minimal sun exposure developing erythema, vesicles and oedema. By the age of two years solar lentigos, xerosis and pigmentation occur. Later in childhood dysplastic and neoplastic lesions occur with the development of actinic keratosis, keratocanthoma, basal cell carcinoma, squamous cell carcinoma and malignant melanoma [1]. In one study the median age for development of malignant melanoma was 8 years of age [2]. Ocular complications are nearly as common as skin lesions with keratitis progressing to corneal opacification, loss of eyelashes, ectropion, entropion and benign and malignant lesions of the cornea and eyelids. Neurological complications occur in approximately 30% of cases and can be severe [1,3].

XP is usually inherited in an autosomal recessive manner with phenotypically normal heterozygotes. There are at least seven different subtypes (complementation groups A-G) as well as XP variants. Various rare forms occur in combination with other disorders such as Cockayne's Syndrome [1]. 80% of patients have classical XP where there is a defect in the initiation of DNA nucleotide excision repair after UV induced damage. In XP variant the defect is found in post-replication or daughter-strand repair.

The diagnosis of XP is considered when a young patient presents with marked photosensitivity, xerosis and multiple pigmented lesions. Phototesting may be performed showing reduced minimal erythema dose in the 290 to 340 nm range [4]. Although phototesting is widely available in the developed world it is neither sensitive or specific for XP. The diagnostic test of choice is time consuming, highly specialised and expensive: cultured fibroblasts are extracted from a skin biopsy, fused with fibroblasts from known XP lines and exposed to UV irradiation. If the subsequent DNA repair is defective, the XP complementation group may be identified from the fused XP line used. Recent developments include the cloning of all XP genes, so the complementation group can also be determined by using recombinant retroviral vectors.

Guatemala has no centralized health records for prevalence of XP or subtype analysis, and to date there has been only one published report of a cluster of cases of the group C complementation form in a single rural Guatemalan community [5]. Of the sub-types, XP-V occurs at a later age and is less debilitating, while XP-C and XP-E sufferers do not usually have neurological complications. XP-A or XP-D are the most likely genotypes to have caused the phenotypic presentation of this patients.

Management of XP consists of early and rigorous photoprotection with sun avoidance, sunscreens and appropriate clothing. Experimental treatments with topical DNA repair enzymes and oral retinoids are showing promise for the future [6,7].