Psychomotor developmental delay and trichorrhexis
nodosa. Mental retardation is secondary to an abnormal cortical cell layer
pattern in the brain and marked microcephaly. The hair defect results from a
reduced content in sulfur matrix protein (mainly because of a half-normal
cystine content), hence the alternative term “trichothiodystrophy” was
suggested for this disease (although this expression is also used to name
the whole group of diseases with this type of hair defect associated with
other ectodermal and neuroectodermal disorders). Microscopically, the hair
defect is characterized by trichoschisis (transverse fractures of the hair);
using polarized light reveals the typical alternation of dark and bright
regions, producing a tiger-tail pattern. In the two children described by
King et al. from unrelated Scottish parents, the head circumference, length,
and weight were below the third percentile at the age of 6 months, which was
associated with developmental delay. Facial features included stubby
eyebrows, protruding ears, and retrognathia. Neurologically, jerky eye
movements, spastic diplegia, and either absent or hyperactive deep tendon
reflexes were noted. Microcephaly with a short skull and small cranial vault, small and bridged sella turcica (radiological) complete the neurological defect. The ectodermal changes included ichthyosis, severe
flexural eczema, and brittle, hypoplastic nails with koilonychia. By the age
of 4 years, photosensitivity of the skin was also reported, whereas all the
other manifestations remained basically unchanged. One patient also
developed bilateral cataracts.